Carbenes = methylenes chlorocarbene

The earbene produced from 5-methyl-5-chloromethylcyclopentadiene gives only 1-methylbenzvalene (33). This shows that the earbene adds to the 1- and 4-positions of the diene component. If the addition occurs at the 1- and 2-positions, the 2-methyl isomer should be formed. The reaction of lithium methylcyclopentadienide with methylene chloride and methyllithium affords 2- and 3-methylbenzvalene both of which are formed by the attack of methylene chloride or chlorocarbene at the unsubstituted carbon of the cyclopentadienide (34). 5-Methyl-5-cyclopentadienyl-carbene was shown by MINDO/3 calculation to have a bisected conformation which seems to be susceptible to 1,4-addition3S). 

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