Cyclopropyl carbene complexes rearrangement

Alkoxycarbene complexes with unsaturation in the alkyl side chain rather than the alkoxy chain underwent similar intramolecular photoreactions (Eqs. 10 and 11) [60]. Cyclopropyl carbene complexes underwent a facile vinyl-cyclopropane rearrangement, presumably from the metal-bound ketene intermediate (Eqs. 12 and 13) [61]. A cycloheptatriene carbene complex underwent a related [6+2] cycloaddition (Eq. 14) [62]. 

The formation of cycloheptadienones from alkoxy(cyclopropyl)carbene complexes and alkynes (Entry 5, Table 2.24) [388,389] proceeds essentially by the same mechanism as the Dotz benzannulation reaction (see Figure 2.32). The cyclopropyl group participates in the electrocyclic rearrangement as the equivalent of a vinyl group. 

The rearrangement exhibits some stereochemical preference for c/s-vinyl carbene complex (with respect to the metal) compared to the //ww-isomer. Thus, 2-methyl-2-m-vinyl cyclopropyl (methoxy) carbene chromium pentacarbonyl rearranges to 5-methyl-5-vinyl-2-methoxycyclopentenone approximately 4 times faster (THF, 52 °Q than the trans-isomer, which in turn rearranges faster than phenyl derivatives. This suggests that vinyl complexes undergo initial Cope-type rearrangement to form metallacycloheptadienes, which then rearrange to jt-allyl complexes. Subsequent CO insertion and reductive elimination leads to the vinylcyclopentenones (equation 89)150. 

The (cyclopropylamino)carbene complex 15 reacted with diphenylalkyne to give a nitrogen ylide, which was converted via thermal A -cyclopropyl to C-cyclopropyl rearrangement and decomplexation to a cyclopropyl-substituted lactam. 

Similarly, the [cyclopropylmethyl(methyl)amino]carbene system reacted to give a cyclopropyl-methyl-substituted pyrrolinone. This cyclopropane-containing aminocarbene complex of chromium underwent alkyne insertion and formation of a heterocyclic ylide. Further rearrangements gave dihydro pyrrolones 17 and 18 with cyclopropylmethyl substituents. ... 

Other reactions of sulphonium ylides include o /9 -elimination,metal-mediated carbene-transfer to olefins, insertion into aromatic C—H bonds or other carbenoid-type processes, formation of Pd" complexes, addition to enones (forming cyclopropyl ketones or heterocycles ), reaction with isoquinoline 2-oxide, and [2,3]-sigmatropic rearrangements " [as in the case of (12) 1 or... 

The rearrangement products (359) and (360) are obtained on oxymercura-tion of cyclodeca-l,2,5,8-tetraene (361). A bridged intermediate (362) is suggested homoallyl-cyclopropyl rearrangement leads to (363), a metal-complexed carbene which is known to undergo hydride shifts as indicated. This mechanism is supported by deuterium labelling. ... 

---