L-ethynyl-2-methylcyclopropane

Unlike the well-known chemistry of the vinylcyclopropane-cyclopentene rearrangement, there is no general method for the rearrangement of alkynyl-cyclopropane to cyclopentene derivatives. One specific example is the pyrolysis of l-ethynyl-2-methylcyclopropane to methylenecyclopentene and other compounds [5]. At 530°C, l-ethynyl-2-methylcyclopropane (1) undergoes a [1,5]-hydrogen shift to give hexa-l,2,5-triene (2), which further isomerizes to methy-lenecyclopentenes 3 and 4 in 38 and 29% yield, respectively (Scheme 1). 

A theoretical investigation of the thermal rearrangements of l-hexen-5-yne, 1,2,5-hexatriene, and 2-methylenebicyclo[2.1.0]pentane has been reported providing a theoretical account of the pyrolysis reactions. The computed energy values are in agreement with experimental product distributions. The thermal C(2)-C(6)/ene cyclization of enyne-allenes has been reviewed. A computation study of the thermal rearrangements of l-ethynyl-2-methylcyclopropane has been reported. " ... 

Pyrolysis of 2-ethynyl-l-methylcyclopropane affords mainly the allene (542) at 340 °C, but at 530 °C the methylenecyclopentenes (543) formed by cyclization of (542) are the major products/... 

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