Methylenecyclopentanes palladium-trimethylenemethane cycloadditions

The discovery of palladium trimethylenemethane (TMM) cycloadditions by Trost and Chan over two decades ago constitutes one of the significant advancements in ring-construction methodology [1]. In their seminal work it was shown that in the presence of a palladium(O) catalyst, 2-[(trimethylsilyl)methyl]-2-propen-l-yl acetate (1) generates a TMM-Pd intermediate (2) that serves as the all-carbon 1,3-di-pole. It was further demonstrated that (2) could be efficiently trapped by an electron-deficient olefin to give a methylenecyclopentane via a [3-1-2] cycloaddition (Eq. 1). 

Acetoxymethyl)-3-(trimethylsilyl)propene (1) is used as a trimethylenemethane precursor in palladium(0)-catalvzed [3 + 2] cycloaddition with electron-deficient alkenes, such as enones, acrylonitriles and a,/ -unsaturaled esters23,26. Mechanistically, this reaction, which gives methylenecyclopentane derivatives 2. is interpreted to proceed via trimethylenemethane-palladium complexes 27,28. 

Other resnlts obtained by Tsnji s group up to 1987 using allyl carbonates are carbony-lations to afford /3,y-nnsatnrated esters " (Scheme 3) (see Sect. VI.3), cycloadditions of trimethylenemethane palladium complex to afford methylenecyclopentanes (Scheme 3), and cycloadditions of zwitterions to afford substituted vinylcyclopentanes (Scheme 4) (see Sect. V.2.5.2). 2-Butene-1,4-diol dicarbonates afford a variety of cyclic strnctnres by reaction with dinncleophiles nnder Pd(0) catalysis (see Sect. I). The first case reported seems to be the formation of the vinylcyclopropane of Scheme 44" ... 

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