Preparation of mixtures of (R)- and (S)-2-(4-alkanoylphenoxy)- o

Details Preparation of mixtures of (R)- and (S)-2-(4-alkanoylphenoxy)- o Preparation of mixtures of (R)- and (S)-2-(4-alkanoylphenoxy)- o

1995-08-11

1998-09-01

Killos, Paul J.

Organic compounds -- part of the class 532-570 series

Organic compounds

Carboxylic acid esters

560 51, C07C 6976

Patent

active

058012729

DESCRIPTION:

BRIEF SUMMARY
DESCRIPTION

The present invention relates to a novel process for preparing a mixture of (R)- and (S)-2-(4-alkanoylphenoxy)- or (R)- and (S)-2-(4-aroylphenoxy)propionic esters of the general formula I ##STR3## where R.sup.1 is aryl, alkyl or aralkyl, and R.sup.2 is alkyl, where the mixture contains an enantiomeric excess of at least 90 mol % of (R) or (S) isomer.
The present invention also relates to the preparation of a mixture of (R)- and (S)-2-(4-acyloxyphenoxy)propionic esters of the formula IV ##STR4## which contains an enantiomeric excess of at least 90 mol % of (R) or (S) isomer, (S)-2-(4-aroylphenoxy)propionic esters I, which contains the appropriate (R) or (S) isomer in said excess, with performic acid or with a mixture of hydrogen peroxide and formic acid.
The present invention furthermore relates to the preparation of a mixture of (R)- and (S)-2-(4-hydroxyphenoxy)propionic acid and/or an alkyl ester of this acid by oxidizing a mixture of the (R) and (S) enantiomers of a 2-(4-alkanoylphenoxy)- or 2-(4-aroylphenoxy)propionic ester I, which contains the appropriate (R) or (S) isomer in excess, and hydrolyzing the resulting mixture of (R)- and (S)-2-(4-acyloxyphenoxy)propionic esters IV with water or aliphatic alcohols in the presence of acidic catalysts.
2-(4-Hydroxyphenoxy)propionic acid and its alkyl esters are valuable intermediates for synthesizing crop protection agents and drugs. They are particularly suitable for preparing herbicidal 2-(4-aryloxyphenoxy)- and 2-(4-hetaryloxyphenoxy)propionic acid derivatives (cf., for example, BE-A 868 875, BE-A 858 618, DE-A 22 23 894, DE-A 24 33 067, DE-A 25 76 251, DE-A 30 04 770, DE-A 32 46 847, EP-A 54 715, EP-A 248 968, EP-A 323 127 and U.S. Pat. No. 4,753,673) in which the herbicidal activity normally derives from one enantiomer. It is therefore desirable also to prepare with maximum enantiomeric purity the intermediates I and IV as well as 2-(4-hydroxyphenoxy)propionic acid and its alkyl esters required to prepare the active substances.
The 2-(4-alkanoylphenoxy)- and 2-(4-aroylphenoxy)propionic esters I are normally prepared by Williamson's ether synthesis from 4-hydroxyphenyl alkyl ketones or 4-hydroxyphenyl aryl ketones and 2-halo- or 2-sulfonyloxypropionic acid derivatives under basic conditions (cf. Acta Polon. Pharm. 20 (1963) 25-30 (see also CA 61 (1964) 8225e), JP 62 178 543, EP-A 0 129 034, EP-A 0 334 595, EP-A 0 334 596, EP-A 0 334 597 and EP-A 0 334 598). However, pure enantiomers cannot be obtained by this method because, according to EP-A 0 380 043, the preferred reaction temperatures for the ether synthesis (80.degree.-100.degree. C.) bring about racemization. The unwanted enantiomer must accordingly first be removed in a subsequent purification step, which is industrially elaborate.
In order to make the optically active 2-(4-acetylphenoxy)propionic esters more accessible, EP-A 0 380 043 proposes carrying out the reaction at temperatures below 50.degree. C. Nevertheless, racemization cannot be completely avoided in every case.
It is furthermore generally known (cf., for example, G. A. Olah, Friedel-Crafts and Related Reactions vol. 3, pages 48 to 50 and 180 to 188, John Wiley & Sons, Inc. (1964) and D. E. Pearson, C. A. Buehler, Synthesis (1972) 533) to react achiral aryl alkyl ethers of the formula V with carboxylic acid derivatives in a Friedel-Crafts acylation: ##STR5##
However, in this case it is unsatisfactory that the 4-acylaryl alkyl ethers are accompanied as by-products by 2-acylaryl alkyl ethers. Thus, for example, the benzoylation of anisole with benzoyl chloride/iron(III) chloride at 150.degree. C. yields 90% para- and 10% ortho-acylation product (cf. DE-A 22 04 973). Separation of the two isomers, eg. by chromatography or distillation, is usually elaborate and associated with loss of required product.
According to EP-A 0 129 034, EP-A 0 334 595, EP-A 0 334 596, EP-A 0 334 597 and U.S. Pat. No. 4,528,394, the 2-(4-acylphenoxy)propionic esters can be converted by oxidation with peracids or peroxide and subsequent hydrolysis int

REFERENCES:
patent: 3383411 (1968-05-01), Schultz et al.
patent: 3954442 (1976-05-01), Becker et al.
patent: 4173709 (1979-11-01), Metivier et al.
patent: 4332960 (1982-06-01), Troesken et al.
patent: 4447256 (1984-05-01), Ohyama et al.
patent: 4528394 (1985-07-01), Otterbacher
patent: 4629493 (1986-12-01), Ura et al.
patent: 4753673 (1988-06-01), Johnston et al.
patent: 4978774 (1990-12-01), Schlegel et al.
patent: 5068052 (1991-11-01), Watanabe et al.
Chem Abst. J6 2178-543.

Affiliated with

Also associated with

Rating

Preparation of mixtures of (R)- and (S)-2-(4-alkanoylphenoxy)- o does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Preparation of mixtures of (R)- and (S)-2-(4-alkanoylphenoxy)- o, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Preparation of mixtures of (R)- and (S)-2-(4-alkanoylphenoxy)- o will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-271278