Photochemical rearrangements of silylcyclopropenes: Cyclopropenes which afford pathways to allenes

Syntheses ofgem-Dihalocyclopropanes and Their Use in Organic Synthesis

“…Its cycloaddition to unsaturated hydrocarbons and alkenes possessing functional groups proceeds rapidly. Many examples of these reactions have been published in the last seven years. ,,,,,,,,− ,,,,,,,,,,,,− …”

Allenes from Cyclopropanes and Their Use in Organic SynthesisRecent Developments

“…25 This is, for instance, the case when 2-benzyl-1,1-dibromocyclopropane ( 27) is reacted with BuLi at -95 °C to afford 2,2′-dibenzyl-1,1′-bi(cyclopropylidene) (28) in 87% yield as a mixture of all possible stereoisomers (Scheme 13). 25a It should also be mentioned that the Doering-Moore-Skattebøl method has been used to convert 1,1-dibromo-2-phenyl-3,3-dimethylcyclopropane ( 29) to 3,3-dimethyl-2-phenyl-1-trimethylsilylcyclopropene (30), 26 which gives an allene when irradiated under the right conditions (see section 2.3). The synthesis is summarized in Scheme 14.…”

“…Kirms and co-workers treated this cyclopropane with 2 equiv of methyllithium followed by chlorotrimethylsilane and obtained 1-trimethylsilyl-3,3-dimethylcyclopropene, which was used to make cyclopropenes 35a-c for subsequent photolysis. 26 When these cyclopropenes were dissolved in pentane and exposed to Pyrex-filtered light from a medium-pressure mercury lamp, they were efficiently consumed and gave in each case an allenylsilane (36) as the main product in good yield (Scheme 15). Compound 30 reacted in an analogous fashion and gave the corresponding allene in 80% yield.…”

“…Compound 30 reacted in an analogous fashion and gave the corresponding allene in 80% yield. 26 Generally it is believed that cyclopropenes rearrange via a vinylcarbene intermediate under both photolytic and thermal conditions. 32 However, when cyclopropene 30 was photolyzed in methanol instead of pentane to trap the conceivable transient vinylcarbene and isolate the expected methoxylated derivative 37, none of the product was detected; the only compound isolated and characterized was 3-methyl-1-phenyl-1-(trimethylsilyl)buta-1,2-diene (36d), which was obtained in quantitative yield (Scheme 16).…”

C–C Bond Cleavages of Cyclopropenes: Operating for Selective Ring-Opening Reactions

“…243 This type of rearrangements were already described, yet they required forcing thermal of photochemical conditions. 244,245 In this case, the use of a platinum(II) catalyst allowed to accomplish the reaction under mild reaction conditions. In particular, the protocol involved the use of 1silyl-2-alkyl substituted cyclopropenes to afford the corresponding allenes using PtCl 2 .…”