Alkenes capto-dative

Two other [2 + 2] cycloadditions on methylenecyclopropane have been carried out with particular alkenes. The first one is the reaction with the capto-datively substituted olefin 496a, which affords the spirohexane cycloadduct 497a in modest yields (Table 39, entry 1) [126]. The low yield is partially... 

These reactions of 1-Me resemble that of (dichloromethylene)cyclopropane [31] and radicophilic alkenes with a capto-dative substitution pattern [32]. Thus, it is not surprising that 1-Me reacts with a-ferf-butylthioacrylonitrile (18), yielding the two isomeric cyclobutane derivatives 19a, b (ratio 2.2 1) as a mixture of two diastereomers each [29] (Scheme 5), and this reaction occurs under milder conditions than the [2-1-2] cycloaddition of 18 onto methylenecyclopropane. 

Alkenes substituted by capto-dative groups such as 5 and 7 undergo cyclodimerization under milder conditions. Mixtures of head-to-head stereoisomers are also obtained in these cases.5,6... 

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