Hydrolysis and desilylation reaction of 2-[(trimethylsilyl)methyl]acrylate (¼ 2-[(trimethylsilyl)methyl]prop-2-enoate) derivatives were studied to evaluate the effect of the presence/absence of a further conjugating substituent (Schemes 3 and 4 and Tables 1 and 2). The substrates having a nonconjugating substituent at the acrylate moiety were stable to dilute alkali conditions, and afforded simple hydrolysis products under concentrated alkali conditions. In contrast, both hydrolysis and desilylation occurred from the substrates bearing conjugated substituents at the acrylate skeleton. The difference in reactivity can be explained in terms of the stabilization of the intermediate anion. During the course of these projects, we previously obtained a-methylene-g-lactones via a cyclization of 2-[(trimethylsilyl)methyl]pentadienoate or the corresponding carboxylic acid [9]. Moreover, ethyl (2Z,4E)-4-methyl-2-[(trimethylsilyl)methyl]hexa-2,4-dienoate (1a) and ethyl (2Z,4E)-3-(cyclohex-1-en-1-yl)-2-[(trimethylsilyl)methyl]-hexa-2,4-dienoate (1b) were hydrolyzed to the corresponding acids 2a and 2b via a typical hydrolysis reaction, i.e., in the presence of aqueous KOH solution in MeOH (Scheme 1). However, the yields of the hydrolysis products 2a and 2b were low (26% for 2a and 31% for 2b). Although not mentioned in the report, the major products were the desilylated acids 3a and 3b. Since direct desilylation from an allylsilane moiety does not occur under such weak-base conditions [10], the desilylation reaction proceeded presumably via an intramolecular assistance of the ester group or its hydrolyzed carboxylate. Indeed, intramolecular attack of an electron-rich anion or related species at the Si-atom as a Lewis base [11] is considered to facilitate protodesilylation. The aim of the present study is to clarify the generality and the substituent effect of this