Aldehydes, cyclopropyl => conjugated

The 1-alkoxycyclopropyllithiums 136 and 140 have been added to a variety of conjugated aldehydes and ketones to produce cyclopropyl carbinols such as 141,... 

Corey s method20 relies on metal exchange with the bromocyclopropane 69 prepared by carbene addition. The extra stabilisation of cyclopropyl anions (chapter 8) makes both this lithium derivative and the ylid 63 more easily handled. Addition to aldehydes or ketones gives mixtures of adducts 70 [it turns out that none of the stereochemistry of 69 or 70 matters] which fragment under Lewis acid catalysis to give the thioacetal 71. Careful hydrolysis releases the 3,4-enal -72, the product of a homoaldol reaction with an aldehyde homoenolate and RCHO and a difficult compound to make as the double bond moves into conjugation very easily. 

Acyl azoliums generated from enals have been converted to cyclopropyl carboxylic esters with ee < 99% by reaction with sulfur ylides. Some FLPs have been found to i react by conjugate P/B addition to unsaturated ketones and esters, whereas 1,2-addition to corresponding aldehydes is usual. ... 

The rearrangements of aldehydes 31 and 32 demonstrated that the ODPM reactivity of P,y-unsaturated aldehydes is not restricted to phenyl-substituted compounds, but can also be extended to systems in which the intermediate biradicals are stabilized by conjugation with a vinyl group. Furthermore, the efficient synthesis of compounds 33 and 34 is of importance because it opens a novel photochemical route to chrysanthemic acid and other cyclopropyl components present in pyrethrins and pyrethroids. In fact, aldehyde 33 can be transformed to irans-chrysanthemic add by simple oxidation. This new s)mthetic route to ecologically benign insectiddes competes with the one previously described by us using the 1-ADPM rearrangement of P,y-unsaturated oxime acetates. ... 

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