Vinylcyclopropane - Cyclopentene Conversion

The conversation of free and Cr(CO)s-complexed 2-vinylphosphirane into 2,5-dihydro-17/-phosphole via 1,3-sigmatropic shifts was studied with DFT and compared with the corresponding vinylcyclopropane-cyclopentene rearrangement (Equation 2) <2002JA13903>. 2-Vinylphosphirane has smaller barriers as in the case of vinylcyclo-propane and the complexed species has still smaller one. The rearrangement of syn- and /F2-vinylphosphirane is a... 

Allenes 23 can also serve as precursors for allyl complexes which undergo intramolecular allylic alkylation to give vinylcyclopropanes 25. This conversion, however, competes with cyclopentene formation. Several other examples of this type have been reported. ... 

More vigorous conditions (190°C) were required to isomerize l,l-dimethyl-2-(prop-2-enylidene)cyclopropane (6) to 3-(l-methylethylidene)cyclopentene (7). This difference can be rationalized by the conversion of 6 to a 1-methylene-2-vinylcyclopropane intermediate which easily undergoes further rearrangement to the live-membered ring. 

Q 1. The conversion of vinylcyclopropane to cyclopentene upon heating is an example of which of the following sigmatropic rearrangements ... 

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