DE1113217B - Process for the preparation of derivatives of partially hydrogenated tetracenes - Google Patents

Description

F30520iVb / 12o

REGISTRATION DATE: ll.'F E B RU AR 1960

NOTICE
THE REGISTRATION
ANDOUTPUTE
EDITORIAL: AUGUST 31, 1961

The invention relates to a process for the preparation of derivatives of partially hydrogenated tetracenes atis ketotetrahydrqnaphthylacetaldehydes or their corresponding ketals.

It has been found * that derivatives of partially hydrogenated tetracenes of the general formula

10

- OH

Process for the preparation of derivatives
partially hydrogenated tetracenes

Applicant:

Farbwerke Hoechst Aktiengesellschaft
formerly Master Lucius & Brüning,
Frankfurt / M., Brüni'ngstr. 45 ' ^!

OH O

wherein R _{1 is} hydrogen or halogen, R _{2 is} hydrogen, alkyl or aralkyl, R _{3 is} hydrogen or methyl and X is hydrogen or the group COOR ₄ in which R _{4 is} alkyl, aralkyl or phenyl, can be prepared in such a way that Aldehydes of the general formulas

Dr. Hans Muxfeldt, Braunschweig,
and DipL-Chem. Werner Rogalski,

Salzgitter-Lebenstedt,
have been named as inventors

R, 0 O

respectively

40

a) in a manner known per se with a malonic acid ester treated in the presence of a condensing agent and the condensation product formed in a manner known per se with an alkali salt of an acetoacetic acid ester or with an acetoacetic acid ester and an alkali metal alcoholate or

b) in a manner known per se with an acetoacetic acid ester in the presence of one. Treated condensation agent and the formed .Kondensationsprodukt in a manner known per se with an alkali salt of a malonic acid ester or with a malonic acid ester and an alkali metal alcoholate, "." '"." ..'-'. ,

C optionally the reaction product for the cleavage of the

^: Treated ketal group in the usual manner with dilute acids and, with exclusion of oxygen, the compound thus obtained is allowed to act in a manner known per se with strongly basic alkylene condensing agents. ■

The method according to the invention is the one

in which R ₁ , R ₂ and R _{3 have} the above meaning, for the sake of simplicity, using the example of the reaction of the O-alkylene-O group and the remainder of an ethylene glycol ketalized ^ -Methyl-S-chloro-S-rnethaliphatic 1,2 - or 1,3-diol is oxy-1 -ketotetrahydronaphthyl- (3) -acetaldehyde (I)

109 680/229

with the ethyl esters of malonic acid and acetoacetic acid shown in the following scheme:

Cl

Malonic acid ester

Cl

CH.O

C Ho ~~ - C. Ho

CH.O

CH ₂ -CH ₂

Sodium acetoacetic acid ester

CH, O acetoacetic acid ester

COOC ₂ H ₅

CHoO

CH2 CHa

COOC ₂ H ₅
O

diluted acids

Sodium malonic acid ester

Cl

CH ₃ OO

COOC ₂ H ₅ OH

O IV

O OH O CH, O O OH O

As starting materials, for example, l-ketotetrahydronaphthyl- (3) -acetaldehyde, 4-methyl-l-ketotetrahydronaphthyl- (3) -acet-

aldehyde,
5-chloro-l-ketotetrahydronaphthyl- (3) -acet-

aldehyde,
8-methoxy-l-ketotetrahydronaphthyl- (3) -acet-

aldehyde,
8-hydroxy-l-ketotetrahydronaphthyl- (3) -acet-

aldehyde,
4-methyl-5-chloro-l-ketotetrahydronaρhthyl- (3) -acetaldehyde,

^ Methyl-S-methoxy-l-ketotetrahydronaphthyl-

(3) acetaldehyde,

S-chloro-S-methoxy-l-ketotetrahydronaphthyl- (3) -acetaldehyde,

^ Methyl-S-chloro-S-methoxy-l-ketotetrahydro-

naphthyl (3) acetaldehyde

or the corresponding ketalized compounds, e.g. B. the ketals with ethylene glycol or propanediol (1,3), in question.

The aldehydes of type B or C which are used as starting materials according to the invention can e.g. B. be prepared by adding aceto

§ 6th

phenones or benzaldehydes with succinic acid esters In some cases it can be useful to use the in

condensed, the alkylidene compound formed cata- the first and second stage as a Reaktiqnskompo- ·

Lytically hydrogenated, cyclized with polyphosphoric acid, residual carboxylic acid ester in excess

if necessary, use the l-ketotetrahydronaphthylcarbon-.

acid ester coalizes, the carboxylic acid ester group to 5 As can be seen from the formula scheme, arrives Hydroxymethyl group reduced, this by one on both ways to the same product, Effect of sulfonic acid chlorides esterified, on a (S-ketotetrahydronaphthylmethyl-cyclqhexa-closing by solvolysis with alkali metal cyanides in the dione (3,5) -2,6-dicarboxylic acid ester, e.g. B. the ethyl corresponding nitrile transferred, the nitrile group to the ester (IV).

Aldehyde group reduced and optionally the io. It should be mentioned in principle that both the

Cleaves ketal grouping with dilute acids. Malonic acid ester as well as the acetoacetic acid ester

The esters of malonic acid and acetoacetic acid must contain the same alcohol component if

those are preferred which, as alcohol, lead to a sterically uniform end product

component a low molecular weight aliphatic wants to come.

Alcohol, especially ethanol, methanol, or 15 In the third reaction stage, this product Araliphatic alcohols, such as benzyl alcohol, for the purpose of cyclization with a strongly basic content. Likewise, phenol esters of the malonic or dense agents, e.g. B. sodium hydride, sodium amide Acetoacetic acid can be used. or sodium dispersions. Here can

The first stage of the process according to the invention also includes a decarbethoxylation in the 4-position

is advantageously carried out in such a way that 20 can be carried out as shown in the equation using the example of

as a condensing agent for the implementation of the pre-implementation of (3-ketotetrahydronaphthylmethyl) -

named aldehydes of type B or C with maloncyclohexadione (3,5) -2,6-dicarboxylic acid ethyl ester (IV)

acid esters, preferably basic compounds, or the ring closure products of the formula V are added

turns. Examples include: salts of tetracene derivatives of the formula VI is shown.

Carboxylic acids with ammonia or amines, alkali 25 The separation of the two products can be advantageous

alcoholates, aluminum alcoholates, alkali hydroxides, can be made chromatographically. The cycli-

preferably piperidine acetate or tertiary aluminization is used in inert solvents,

nium propylate. preferably in aromatic hydrocarbons, such as

The reaction conditions can be varied in terms of benzene or toluene, or in aromatic-aliphatic solvents, as well as in terms of the 3 ° ethers, such as anisole, or in high-boiling cyclic temperatures. Aether works appropriately. The reaction temperatures should be at temperatures between 20 and 120 ⁰ C, pre about lie between 80 and 140 ⁰ C. Preferably at the boiling point of the settlement used for the success of the reaction is that one solvent. The solvents used are, for example, when oxygen is excluded,
wise suitable: aromatic hydrocarbons, such as 35. Of compounds of type A, it is known benzene or toluene, and aliphatic and cyclic (J. Am. Chem. Soc, Vol. 75, 1953, p. 5455) that they are in ether, such as Diethyl ether, dioxane or tetrahydrofuran. Presence of strong or weak bases. Ring cleavage

Suffer the obtained in the manner described above. It was therefore not to be expected that the

Condensation product is then in the ring closure by the method according to the invention,

second stage with an alkali salt, preferably the 40 starting from the above-mentioned (1-ketotetrahydro-

Sodium or potassium salt of acetoacetic ester um- naphthylmethylj-cyclohexadione dicarboxylic acid esters,

set. Instead of an alkali salt one can also succeed.

well an acetoacetic ester and an alkali metal alcoholate. In Angewandte Chemie, Vol. 71, 1959, p. 346; turn around. Possible solvents are: Chemischeberichte, Vol. 92, 1959, pp. 3122 to 3150, Alcohols, preferably ethyl alcohol, _ the above 45 and J. Am. Chem. Soc, Vol. 81, 1959, pp. 1006/1007, mentioned aliphatic and cyclic ethers and are already methods for the synthesis of tetraaromatic Hydrocarbons, such as benzene or cyclic compounds, have been suggested that Toluene. It is an advantage, but invariably lead to anhydrotetracyclines when used, of alcohols to use those which are already available as those by these known processes However, alcohol component in the above-mentioned 5 ° anhydrotetracyclines have no practical given reaction stage existing malonic acid importance, since the pharmacological effectiveness in esters are present. the anhydride series is much lower than in the

The first reaction stage can also be carried out by a tetracycline series and a conversion of anhydrous

lead to the fact that the aldehydes of type B tetracyclines were converted into the corresponding tetracyclines so far

or C is not yet possible in the presence of one of the abovementioned Kon-55. In addition, anhydrous

Densant with an acetoacetic acid ester betracycline due to the dehydration

acts and then in the second stage the associated aromatization of the ring C im

formed condensation product with an alkali salt in contrast to the process products, which

of a malonic acid ester. The reaction according to the invention are obtained, both against

In this case, the conditions are the same as those for acids and bases to a large extent

have already been stated above. resistant, so that the use of strong bases

If you use nothing in the way of the first reaction stage in syntheses in the anhydride series

Aldehydes of the formula C as starting materials, it will stand.

the ketal products from the reaction products obtained are valuable intermediate groups by the action of dilute acids, e.g. 65 products and, since they form the ring structure of the tetracyclines dilute mineral acids or Lewis acids, such as contained, in particular for the construction of pharmaceutical, Zinc chloride and boron trifluoride, in a keto group, are valuable compounds of this body class convicted. suitable.

$ 7

The Roman 360 mg desdimethylamine p ^ l ^ ä-bisdeoxydescarbox digits used in the following example refer to the formula scheme. . amidochlorietracycline-IQ-methyläither (VI).

Example 1 ' ^: '■; Compound of Formula V

a) A mixture of 12.5 g of the aldehyde .der; 5 C ₂₃ H ₂₃ O ₇ Cl (molecular weight = 446.9): Formula I, 350 ecm absolute benzene, 7.6 ecm mayon. p ^. ^^ η - «ι cn ο / tr - <on ο / acid diethyl ester, 1 g piperidine and 4 ecm glacial acetic acid £ unde7 ^: '''" C - % 220 / S - 5410 / is boiled for 14 hours on a water separator. Angerunaen. ......, u - oz ^ z / ₀ , - η - d, 4J / _o .

Finally, the solution with dilute hydrochloric acid, ■ UV absorption maxima in n / 100-methanolic

dilute sodium bicarbonate solution and finally V> hydrochloric acid: l _max 223, 258 and 328..ιημ; in n / 100 metha-

Washed with water, in a vacuum from the sodium hydroxide solution: 223 ^ 260 and 337 πιμ. ;

means freed and what remains. Oil in portrait - IR absorption _maxima:; 3.47, 5.84, 6.00, 6.21

vacuum dried at 130 ⁰ G for 1 hour. It will be like this (secondary maximum), 6.37, 6.89. : -..-..-.

17.56 g (96% of theory) of crude Alkyhdenmalon- With ■ iron (in) chloride _: in methanol gives the

Acid ester of the formula II obtained, which for a further 15 binding of the formula V a green color reaction,

Cleaning dissolved in benzene petroleum ether (8: 2) and ._.-, ■ -. ; -.-- .. "'....

is filtered through silica gel. The filtrate is in. ·. ... "Compound of formula VI. -.

Evaporated in vacuo and the colorless oil (11.22 g) C ₂₀ H ₁₉ O ₅ Cl (molecular weight = 374.8): - -

processed without further purification. Calculated for analysis '' P -64090 / _H - SU 0 / ■

a small amount was distilled in a high vacuum *> ■ 'S ^ -'" ^V C =. U 26 ° [ H = 5 43 <V '

C ₂₃ H ₂₉ O ₇ Cl (molecular weight = 452.9): '". The UV absorption niaxima in ji / 100-methano-calculated. C = 61.10%, H -6.47%; Hydrochloric acid or n / 100-methaiolic sodium found C = 59.99%, H == 6.43%. - - alkali of the compounds of the formulas V and VI - are

■ ■ :. ψ practical, idsotic. ^r '....; .- ■ ..-. -...- ■ - "

IR absorption maxima (in chloroform) between IRr absorption maxima; 3.48, 5.88, 6.00, 6.21, 6.40,

2.5 and 7 μ: 3,47,5,88,6,15,6,40, 6.90 μ .. .-., - .... 6.90, μ,, -.:. -. ..

b) 4.7 g of the alkylidene malonic acid ester of the formulas, the IR absorption spectra of the two compounds 70 cm absolute ether, 1.4ccm acetoacetic acid ethyl fertilizer, the formulas V and VI differ ester and 800 mg of sodium ethylate are 3 ° through the intensities at 24 hours. the different maxima, Boiled on the reflux condenser. The reaction mixture in particular, however, in that the connection is extracted with water, the aqueous one. Extract according to formula VI instead of a.,. Secondary maximum at acidifies and the precipitating product III with 6.21 μ occurs a new maximum.

Chloroform extracted. To split the ketal of,,. . _ ... -, ..-. . , ·.

Formula III you shake the. Chloroform extract ψ .. '. ". -. -. Öetspief 2..

1 hour with 10% aqueous hydrochloric acid, it washes a) 21.5 g of the aldehyde of the formula I, 12 ecm malonic

with water, the solvent is distilled after the dimethyl ester, ^, ccm glacial acetic acid; 1.8 g piperidine

Dry completely with sodium sulfate and acetal and = 350 ccrn benzene are 2 hours on

receives 2.28 g of the compound of the formula IV.. Water separator- under reflux :, boiled. . The GE-

. UV absorption maxima in, n / 100-methanolic 4; ° mixing is then carried out with Sada solution and water

Hydrochloric acid: X _ma x 252 and 326 πιμ; in. n / 100-methano- wash, dried over sodium sulfate and concentrated

Lischer caustic soda: 260, 284 and 326 πιμ. . _; . steams after the recrystallization of the back.

IR absorption maxima in chloroform: 3.40, 5.82, from ether you get 24gdes.Kondensationsi

6.00. 6.28, 6.39, f>, 89 µ. -.- ■ ". · '-, product (82% theoryXvQm melting point 96 ° C«

c> XM of the obtained ^ connection of the. Formula IV 45- C ₂₁ H ₂₅ O ₇ Cl (molecular weight = 424 _; 9): are m 50 ecm freshly distilled over lithium alanate- ■ t>'τ,' ^ ¹ - ^: «f« οι ti <niw ■ '" tem . anisole with rigorous oxygen and Feuchfig- Calculated ν ...:.. C = 59.40 / _OJ H. = 5.93 / _p; keitsausschluß with 6ecm on the one 20% sodium geiunäen ..... C .- ^ 59.36 J ₀ ,. H = ^ 5.91- J ₀ .... Hydride dispersion in xylene for 5 hours at 120 ° C bX To a mixture of 1.13 g of sodium methylate, heated. Excess sodium hydride is decomposed for 5? ? 16 cc of methanol and 2, .- cc-AeetessigsAuremethyI with dilute methanolic hydrochloric acid, diluted ester are added eine.Lösung · _of; 10j2 g; of the above, the Reaktionsgemiseh with ether and washed with described condensation product in 150 cc of diluted hydrochloric acid and water. The organic phase, dried over sodium ether and boiled for 3 hours under re-sulphate, is flowed in vacuo. That which crystallizes out during the reaction is completely freed from the solvent it, the residue 55 sodium salt is filtered off with suction and washed with ether, dissolved in chloroform and adsorbed on silica gel. Yield: 4.5 g. ^ The mother liquor and the combined. When washing with chloroform, a washing liquid is extracted with it. Water, acidifies yellow, intensely green fluorescent zone, snow the extract with dilute hydrochloric acid except for one through the column. It is initially followed by an almost colorless ρκ value of 4.5 and the separating zone, which contains the compound of the formula VI, and ⁶ «dend reaction product (second fraction) are extracted with a pale yellow-colored zone containing the ethylene chloride . The extract is bonded to the formula V containing sodium sulfate. The eluates of both zones are dried and concentrated under reduced pressure, and are evaporated separately under nitrogen and evaporated (yield 1.9 g).

the residues are dissolved in ether and after the sodium salt (4.5 g) is dissolved in 20 ecm metha-

Concentrate the ether extracts carefully with petroleum ether ⁶ 5 nol, dilute the solution with 150 ecm of water and

injected. This gives 448 mg acidified with dilute hydrochloric acid to a pH value

Desdimethylamino - 6.12a - bisdeoxydescarboxamido- from 4.5 to. . The precipitating reaction

4-carbäthoxychlortetracycline-10-methylether (V) and product (first fraction) is also with methylene.

extracted chloride and, as described for the second fraction, worked up further (yield 4 g). The total yield of 3- (2,6-dicarbomethoxyhexadione- (3,5) -ylmethyl) -4-methyl-5-chloro-8-meth- oxy -1 - ketotetrahydronaphthylene ethyl ketal accordingly 5.9 g (49% of theory).

C ₂₄ H ₂₉ O ₉ Cl (molecular weight = 496.9):

Calculated C = 58.08%, H = 5.88%;

found C = 57.80%, H = 5.96%.

c) 4.3 g of the compound described above is dissolved in 50 cc of methylene chloride and 50 cc of 4% strength hydrochloric acid, ^it Va 2 hours at room temperature shaking. After the hydrochloric acid has been separated off, the organic phase is dried over sodium sulfate and evaporated under reduced pressure, the residue (3.9 g) is dissolved in 100 ecm anisole freshly distilled over lithium alanate and at HO ⁰ C under the purest nitrogen with 10 ecm 20% ^r sodium hydride dispersion added. After the end of the first stormy evolution of gas, 1 ecm of a mixture of two times 0.05 ecm of methanol and 10 ecm of anisole is added to the solution, while stirring. The new gas evolution takes about 15 minutes. After this has subsided, 5 ecm sodium hydride dispersion is added to the mixture every 15 minutes. The reaction mixture is stirred for a further 15 minutes and, after cooling under nitrogen, carefully acidified with a mixture of concentrated hydrochloric acid-methanol (1: 1). The light yellow reaction product is mixed with 200 ecm of ether and, after washing with water and drying over sodium sulfate, all of the solvent is distilled off under reduced pressure. The residue (3.6 g) is dissolved in chloroform-butanol (200: 1) and adsorbed on acidic silica gel. When washing with the same solvent mixture, a zone containing starting material first migrates through the column. This is followed by a second zone containing the ring closure product, the eluate of which is evaporated. After the residue has been recrystallized from acetone-ether, the yield is 700 mg (20% of theory). The product melts at 212 to 215 ^° C. with decomposition.

C ₂₂ H ₂₁ O ₇ Cl:

Calculated C = 61.03%, H = 4.89%;

found C = 60.98%, H = 4.88%.

Example 3

1.34 g of 3- [2,6-dicarbomethoxyhexadione- (3,5) -ylmethyl] -4-methyl-8-methoxy-1-ketotetrahydronaphthalene are dissolved in 40 ecm anisole freshly distilled over lithium alanate, under nitrogen with 2 ecm sodium hydride dispersion and, after heating to 100 ⁰ C with 1 of a mixture of 0.1 cc of methanol and 30 cc of anisole ecm added. After the initially vigorous evolution of gas has ceased, a further 2 ecm of sodium hydride dispersion is added to the reaction mixture and heated to HO ⁰ C for a further 15 minutes. After cooling, excess sodium hydride is decomposed with a mixture of methanol-concentrated hydrochloric acid (1: 1) and the acid Solution diluted with water. The reaction product is extracted with ether, the solution is dried over sodium sulfate and the solvent is completely distilled off. The residue is taken up in chloroform and adsorbed on silica gel. When washing with chloroform-butanol (250: 1), a yellow zone quickly migrates through the column. Your yellow, intensely green fluorescent eluate is evaporated and the residue is recrystallized from acetone-ether. The yield is 375 mg (30% of theory); Mp. 188 to 196 ° C with decomposition.

C ₂₂ H ₂₂ O ₇ (molecular weight = 398.4):

Calculated ... C = 66.32, H = 5.57.0CH ₃ = 15.58%; found ... C = 66 ₃ 37, H = 5.55, OCH ₃ = 15.36%.

Example 4
a) 4.57 g of the aldehyde of the formula

CH, O

CH ₂ -CH ₂

2.25 ecm of dimethyl malonate, 1.1 ecm of glacial acetic acid and 0.43 g of piperidine acetate are refluxed in 90 ecm of benzene 2V for ₂ hours on a water separator. The cooled solution is then washed with dilute sodium hydrogen carbonate solution, washed neutral with water, dried and evaporated under reduced pressure. The oily residue is made to crystallize by spraying with ether. Yield: 4.4 g (67% of theory) of Schmp._126 to 13O ⁰ C. For analysis, a sample was recrystallized from ether (m.p. 130 to 132 ° C.).

C ₂₀ H ₂₃ O ₇ Cl (molecular weight = 410.9):

.. Calculated C = 58.47%, H = 5.64%;

found C = 58.60%, H = 5.90%.

b) 2.9 g of the compound of the formula thus obtained

COOCH ₃

COOCH ₃

CH ₃ O

CH ₂ -CH ₂

are in a solution of 870 mg of tertiary potassium butoxide and 0.93 ecm of methyl acetoacetate in 5.8 ecm of absolute methanol suspended. After adding 60 ecm of absolute ether it becomes clear Solution refluxed for 5 hours. The precipitated during this time crystallized The potassium salt of the reaction product is filtered off and washed with ether. Yield: 1.54 g (53% of Theory).

109 680/229

c) 1.54g of the potassium salt of the compound of the formula

Cl

CH ₃ O

CHo-CH.

are suspended in 50 ecm of water which is brought to a ρπ value of 5 with dilute hydrochloric acid. Then it is extracted with ether, the ether extract is washed, dried and evaporated. The residue is dissolved in 5 ecm of acetone and 150 mg of p-toluenesulfonic acid are added to the solution. After 2 hours, the solution is mixed with 50 ecm of chloroform and the mixture is washed neutral with water. The chloroform solution is washed with water and evaporated. The residue is dissolved in 20 cc of anisole and the solution was treated at 8O ⁰ C under air and moisture with 2 cc of a 30% sodium hydride dispersion in xylene, the mixture heated to 130 ⁰ C and treated it after 20 minutes with a further 2 ecm sodium hydride dispersion. 20 minutes later, the mixture is cooled and poured into 30 ecm of glacial acetic acid under nitrogen. The resulting yellow solution is diluted with water and the reaction product is extracted with ether. The extract is then washed three times with water, dried over sodium sulfate and completely evaporated. The yellow residue is dissolved in a little chloroform and adsorbed on silica gel. When washing with chloroform and 0.2% n-butanol, a light yellow zone quickly migrates through the column. It is followed by a second orange-colored zone, the eluate of which is evaporated under reduced pressure. The residue of this eluate crystallizes when sprayed with a few drops of acetone. The crystals are filtered off with suction and recrystallized from acetone-ether. The yield of the compound of the formula

Cl

CH, 0

OH O

55

is 28% of theory. The almost colorless crystals melt at 177 to 178 ^° C. with decomposition.

C ₂₁ H ₁₉ O ₇ Cl (molecular weight = 418.8): Calculated ... C = 60.22, H = 4.57, OCH ₃ = 14.82%; , found ... C = 60.21, H = 4.45, OCH, = 14.59%

UV absorption: l _max 449 (31600), 348 (4900), 312 (6700), 280 (5600), 261 (5500) ηιμ (measured 1 hour after the addition of borax).

IR absorption: Imax 3.36, 5.75, 5.83, 6.17, 6.32, 6.50, 6.79, 6.98 µ.

Claims (1)

PATENT CLAIM:
Process for the preparation of derivatives of partially hydrogenated tetracenes of the general formula OH OH O where R ₁ denotes hydrogen or halogen, R ₂ denotes hydrogen, alkyl or aralkyl, R ₃ denotes hydrogen or methyl and X _{denotes hydrogen or the group COOR 4} in which R ₄ denotes alkyl, aralkyl or phenyl, characterized in that aldehydes of the general Formulas R ₂ O respectively in which R ₁ , R ₂ and R _{3 have} the above meaning and the group O-alkylene-0 represents the radical of an aliphatic 1,2- or 1,3-diol, a) treated in a manner known per se with a malonic acid ester in the presence of a condensing agent and the condensation product formed in a manner known per se with an alkali salt of an acetoacetic acid ester or with an acetoacetic acid ester and an alkali metal alcoholate or b) in a manner known per se with an acetoacetic acid ester in the presence of a condensing agent treated and the condensation product formed in a manner known per se with an alkali salt of a malonic acid ester or with a malonic acid ester and an alkali alcoholate, if appropriate, the reaction product for cleavage of the ketal grouping in a customary manner with dilute Treated acids and in the absence of oxygen on the compound thus obtained can act in a known manner strongly basic condensing agent. Considered publications:
Angew. Chem., Vol. 71, 1959, p. 346;
Chemical Reports, Vol. 92, 1959, pp. 3122 to 3150; J. Am. Chem. Soc, Vol. 81, 1959, pp. 1006/1007. © 109 680/229 8.61