Cyclopropanone equivalents 1,1,-disubstituted

In this chapter, we will review methods for preparing cyclopropanones, their physical and spectroscopic properties, and the nature of their reactions with nucleophiles, electrophiles and in cycloaddition processes. Another part of the chapter will deal with cyclopropanone equivalents, 1,1-disubstituted systems which under certain conditions may provide carbonyl-related derivatives of the parent ketones. We will also discuss the role of cyclopropanones in biological phenomena and cite specific examples of the use of cyclopropanone intermediates as key units in the synthesis of natural products. 

Among the systems which have played the role of cyclopropanone equivalents have been cyclopropane derivatives containing both a secondary amino group and a hydroxyl substituent on the same carbon atom. These 1,1-disubstituted carbinol amines appear to be in equilibrium with the corresponding iminium salts and thereby act as reactive electrophilic sites for attack by a variety of nucleophiles. 

Displacement reactions on 1,1-disubstituted cyclopropanes have been used to prepare other cyclopropanone equivalents. The most readily available 1,1-disubstituted cyclopropanes are geminal dihalo derivatives prepared by the addition of dihalocarbenes to olefins. Unfortunately, these materials do not undergo direct displacement easily and therefore do not provide a general route to other cyclopropanone derivatives. Solvolysis usually leads to ring-opened products, although dibromocyclopropanes with a barrier to... 

As discussed in an earlier section, displacement reactions on appropriately 1,1-disubstituted cyclopropanes may give rise to new cyclopropanone equivalents (see Schemes 43, 44). These reactions occur by S 1 processes involving carbenium ions of structure 136. In addition to being susceptible to ring-opening (Scheme 18) and trapping... 

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