Acylgruppenwanderung, II¹⁾ Enolester des α‐Acetylacetophenons und des α‐Formylacetophenons

Abstract

Bei der 0-Acylierung des a-Acetylacetophenons mit Acetylchlorid, Chlorkohlensauremethylester und N,N-Dimethylcarbamoylchlorid entstehen Enolester, die in den vier isomeren Formen 1Z, lE, 2 2 und 2E vorliegen konnen. Einige dieser Isomere wurden rein isoliert, alle iibrigen lieI3en sich 1H-NMR-spektroskopisch einwandfrei nachweisen. Zwischen den beiden Z-Isomeren stellt sich durch schnelle 1,5-Acylgruppenwanderung ein thermisches Gleichgewicht ein. Der Ubergang von der 2-in die E-Reihe wird photochemisch erreicht. a-Formylacetophenon bildet mit Chlorkohlensaure-methylester bei 0°C vorwiegend das 2-Isomer 62, das sich thermisch in das stabilere E-Isomer 6E umlagert.Acyl Group Migration, 111) -Enol Esters of a-Acetylacetopbenone anda-Formylacetophenone 0-Acylation of cc-acetylacetophenone with acetyl chloride, methyl chlorocarbonate and N,N-dimethylcarbamoyl chloride leads to four isomeric forms of enol esters: lZ, 1E, 2 2 and 2E. Some of these isomers have been isolated in pure state, others could be identified in solution by IH-NMR spectroscopy. The two 2 isomers equilibrate via a rapid thermal 1,5 acyl shift. The transformation 2 Z E is effected by radiation. Acylation of a-formylacetophenone with methyl chlorocarbonate at 0°C leads predominantly to the 2 isomer 6 2 ; this rearranges thermally to the more stable E isomer 6E.

Carbonotropy

“…Upon acylation of 1,3-diketones with acetyl chloride, an approximately 1 : 1 mixture of the Z (XLIX) and E (L) isomers is formed in almost all cases [90][91][92][93][94][95][96] so that the IH-NMR spectrum reflects, at low temperature, the signals of both isomers (Fig. 2.8).…”

Dissociative and Photochemical Mechanisms of Intramolecular Tautomerism

“…This is explained by an unfavored orientation of the interacting orbitals of the electron lone pair in nitrogen and the carbonyl group [36,37). An analogous method for the initiation of acyl transfers has been used by Hartke and coworkers [39][40][41][42] The same basic reaction scheme was found [23,43,44] to operate in photoinitiated acylotropic rearrangements of N-acylaminomethylene derivatives of 3(2H)benzo( b )thiophenones and their analogs XVlIa. However, the rearrangement XVa ~ XVb proceeds rapidly and completely upon UV irradiation of solutions of XVa, leading to the intermediate formation of the E-isomer XVc, whose structure meets the steric requirements of the 1,3-acyl transfer reaction.…”