Cyclopropyl ring, conjugation

Substituted cyclopropyl rings conjugated with a triple bond system have recently received attention as C5 building blocks. The procedure described here is a modification of the decarboxylation-elimination reaction for the preparation of a.3 acetylenic acids from enol sulfonates of acyl malonates. Addition of aqueous alkali to the enol sulfonate of diethyl cyclopropyl carbonyl malonate gives cycl opropyl propiol ic acid, but the yield is 1 ow. 

In some cases, conjugate addition has been performed on systems where a double bond is conjugated with a cyclopropyl ring. An example is ... 

This increased stability has been explained between the bent orbitals of cyclopropyl rings and the vacant p orbital of the cation carbon. The vacant p orbital lies parallel to C2-C3 bond of the cyclopropane ring and not perpendicular to it. Thus the geometry becomes similar to that of a cyclopropane ring conjugated with an oblefinic bond. 

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