Carbene benzene addition mechanism

The mechanism proposed by Shephard and Rooney (95) involved a (T-7i-l,2,5-triadsorbed species for the dehydrocyclization of o-ethyltoluene and a n-allylic species for the dehydrocyclization of propylbenzene (Scheme 41). We suggest, instead, a carbene-benzene addition mechanism, in better agreement with the general picture we have given for 1-5 and 1-6 ring closure (Scheme 81). 

In view of the smooth addition of carbanions to the electrophilic P atom of phosphorins (see p. 78 and 66), Markl and Merz attempted the addition of carbenoids (carbenes ) by reacting dichloromethane, trichloromethane or dichloro-phenylmethane with potassium-tert-butoxide in the presence of 2.4.6-triphenyl-X -phosphorin 22 or 2.4.6-tri-tert-butyl-X -phosphorin 24. The desired bicyclocompound 7/5 or the X -phosphepin 116 were not obtained. Instead, benzene derivatives were formed by loss of a PCI fragment, the fate of which was not determined. Markl has proposed a mechanism in which intermediates 114,115 and 116 ZK invoked ... 

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