Allylidenecyclopropane rearrangement

With unsaturated aldehydes as the carbonyl component in the Peterson step, dienes are produced which undergo a double ring expansion via the allylidenecyclopropane rearrangement to give 7,5-fused ring systems such as 77.86... 

The thermal allylidenecyclopropane rearrangement, applied to bicyclo[4.1.0]heptane derivatives leads via a remarkable double ring expansion, to bicyclo[5.3.0]decane derivatives, particularly hydrazulenes. The rearrangement took place with significant stereocontrol making many synthetically useful transformations accessible (Table 8). 

Oxaspiropentanes have been generated and rearranged in a large variety of different environments. A series of alkylidene- and allylidenecyclopropanes, present in the structures of bicy-clo[3.1.0]hexanes or bicyclo[4.1.0]heptanes, were epoxidized and rearranged in situ to bicyclic ketones with the alkyl or allyl group preferentially to exclusively in the exo position (Table 4).51 This corresponds to a preferential to exclusive epoxidation of the corresponding alkenes from the sterically less demanding exo face. 

Surprisingly, 2-vinylcyclobutylidene undergoes exclusively carbene rearrangements leading preferentially to the allylidenecyclopropane. 

Similarly, treatment of an allylidenecyclopropane 3 with hydrogen chloride gave the ring-conserved product 4 and the allylic rearrangement products 5 and 6 in a ratio of 3.5 1 1 (for additional information on methylenecyclopropane rearrangements see Section 2.4.1.1.). 

Table 8. Formation of Hydrazulenes and Other Bicyclic Systems by Rearrangement of Fused Allylidenecyclopropanes...

Double and even triple Heck-Diels-Alder cascade reactions involving bicyclopropyli-dene and 1,4-diiodo- or 1,3,5-triiodobenzene, respectively, have been accomplished. In these sequences, the carbopaUadation across the highly strained alkene is followed by a cyclopropyhnethyl to homoallyl rearrangement with concomitant /3-hydride elimination to yield an allylidenecyclopropane, which subsequently undergoes a smooth [4 + 2] cycloaddition to furnish the spiro[5.2]octene moiety (Scheme 4). ... 

It is, however, interesting that the rearrangement of allylidenecyclopropanes fused to five- and six-membered rings do show stereospecificity in a thermal double ring expansion. Thus, Cohen showed that the trans- and c/5-7-butenylidenebicy-clo[4.1.0]heptanes give different stereoisomers of 8-methylbicyclo[5.3.0]deca-l(2),9-diene (Scheme ini) " ... 

Semmelhack and DeFranco " have reported the thermal rearrangements of some chlorinated derivatives of spiro[2,3]hexa-4-ene and -diene. Compound (409a) gives the expected allylidenecyclopropane in good yield but, remarkably, a temperature of 440 °C is required for thermolysis of (409b). Cl Cl... 

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