ChemInform Abstract: Generation and Reactions of Lithiated tert. Butyl and 2,6‐Di(tert‐butyl)‐4‐methylphenyl Cyclopropane Carboxylates.

Abstract

(14.VI1.86) trrf-Butyl and 2,6-di(tert-butyl)-4-methylphenyl (RHT) cyclopropanecarboxylates (4, 6, 24, 25) are lithiated with LiN(i-Pr), and t -BuLi, respectively. Reactions with alkyl halides, aldehydes, acyl chlorides, and heteroelectrophiles give a-substituted BHT esters which can be cleaved (t-BuOK/H,O/THF) to the corresponding carboxylic acids or reduced (LiAIH,/THF) to the cyclopropdnemethanols.Though cyclopropane (la) itself is more acidic than the less strained cycloalkanes and open-chain alkanes (cf. lb) [l] [2], the relative acidity of the corresponding derivatives with conjugatively electron-withdrawing groups (EWG) may be reversed (2a less acidic than 2b), as shown by many mechanistic investigations with various EWG's (COR [3- [ll]). This effect is normally ascribed to the increase in strain upon introduction of a trigonal center into a three-membered ring [12] (compare 3a with 3b). Pyramidalized carbanion centers or C-atom rather than heteroatom-metalated structures (compare 3a with 3c) are, therefore, discussed for such species3). Alternatively, the carbanionoid species can be stabilized by decoupling to a diradical, see 3d [17] [18]. Hitherto, it was not possible to isolate suitable single crystals for X-ray structure analysis to obtain insight about the bonding in such species.Besides these physical organic aspects, synthetic applications of EWG-substituted cyclopropyl nucleophiles have been studied extensively. A list of leading references to papers in which the successful generation and reactions with electrophiles of metalated ') , ) 3,Part of the projected Ph. D. thesis of R . H . , ETH Zurich.Part of the Master's thesis of Th.M.. ETH Zurich, 1985. For the question as to whether a pyramidal ketonic carbanion exists or not, see [13-161.