4- -2-methyl-1 methylenecyclopentane

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). 

These methylenecyclopentane annulations may also be applied to conjugated dienones, e.g., 4-methyl-4-[2-(trimethylsilylmethyl)-2-propeny[]-3-vinyl-2-cyclohexenones43 44. Again, fluoride ion was used successfully to generate either octahydro-5//-inden-5-ones or hexahydro-2( 1H (-pentalenones. 

METHYLENECYCLOALKANES 2,4,6-TliisoprO-pylbenzenesulfonyl hydrazine. a-METHYLENECYCLOBUTANONES Chloro-[(trimethy lsily l)methyl]ketene. METHYLENECYCLOPENTANES 4-Chloro-2-lithio-1-butene. 

Nickel catalyzed [3 + 2] cycloadditions of methylenecyclo-propane and 2,2-dimethylmethylenecyclopropane with (4) afford 3-methylenecyclopentane derivatives with extremely high TT-face selectivities (91% and 98% de respectively) five alternative auxiliaries were found to be less effective. - Palladium catalyzed [3 + 2] cycloaddition of 2-(TMS-methyl)-3-acetoxy-l-propene with an N-enoylsultam, however, proceeds with disap-... 

Asymmetric [3 + 2] cycloaddition of 2-(sulfonylmethyl)-2-propenyl carbonate 56 with methyl acrylate or methyl vinyl ketone is also catalyzed by the palladium-ferrocenylphosphine 8b complex to produce methylenecyclopentane derivatives with up to 78% ee (Scheme 2-36) [52]. 

Therefore, in the presence of phosphane-free or phosphane-modified Ni(0) catalysts, alkyl acrylates and alkyl crotonates codimerize with 2-methyl- and 2,2-dimethyl-methylenecyclopropanes to give Type B cycloadducts. The reactions turn out to be regio- but not stereoselective. The methyl group(s) bonded at the three-membered ring are always found at C-2 of the resulting methylenecyclopentanes, whereas the electron withdrawing group is bonded to C-4 (Eqs. 86 and 87) 27). 

Another interesting point is the regioselectivity of these [3+2]-cyeloadditions. Whenever a 2-substituted methylenecyclopentane is detected in a codimerization, catalyzed by a Pd(0) compound, the substitution pattern is the same as found in [3 -f 2]-cycloadditions starting with 2-[(trimethylsilyl)methyl]allyl acetates 183) (Eq. 85). 

Other 1,3-dienes, such as 1,3-butadiene, isoprene and methyl-2,4-pentadienoate, either do not react with methylenecyclopropanes or yield only 3-vinylmethylene-cyclopentane derivatives exclusively (Table 10 and Eq. 114). Quite unexpectedly, methyl-2,4-pentadienoate reacts only at the terminal C=C bond, giving a vinyl-methylenecyclopentane in poor yield 224) (Eq. 114). 

Cyclopolymerization of 2-methyl-l,5-hexadiene is catalyzed by a cationic zir-conocene complex [75]. Isolation of methylenecyclopentane derivatives 55-57 from the low molecular weight oligomeric products provides convincing evidence for chain transfer via P-methyl elimination. 

In the presence of scandocene hydride 63,3-methyl-l,4-pentadiene is catalyt-ically converted to methylenecyclopentane and its isomer via cyclobutylmethyl-metal intermediate 64 [80]. 

However, a completely different selectivity pattern is observed in the analogous reaction of 5 with methyl acrylate. Methyl 3-hexylidenecycIopentanecarboxylate (9) is the major product (EjZ 2 1), whereas a mixture of the 2- and 4-pentyl-substituted methylenecyclopentanes 7 and 8 is additionally obtained. 

However, methyl acrylate reacts with l-methyl-2-methylenecyclopropane to give a 43% yield of a 70 30 (cisjtrans) isomeric mixture of methyl 3-methyl-4-methylenecyclopentane-carboxylate. ... 

Starting contemporaneously with Skinner, Turner s group (Turner et al., 1957) published a much larger body of work ending in 1973. Turner s work produced a substantial amount of data on the relative stability of isomers, for example, exo-endo isomers like methyl-cyclopentene and methylenecyclopentane. 

Cycloaddition.2 In the presence of this nickel catalyst, methylenecyclo-propanes undergo an unusual cycloaddition across carbon-carbon double bonds. Thus methylenecyclopropane (1) when heated in a sealed tube (60°, 48 hrs.) with excess methyl acrylate in the presence of bis(acrylonitrile)nickel(0) gives the 1 1 adduct, methyl 3-methylenecyclopentanecarboxylate (2), in 82% yield. Methyl vinyl ketone or acrylonitrile is also a suitable substrate. The reaction provides a useful synthesis of methylenecyclopentane derivatives. 

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