Cyclopropanation of a, /3-unsaturated carbonyls

Chiral acetals have also been used as chiral auxiliaries for the enantioselective cyclopropanation of a,/3-unsaturated carbonyl derivatives (Figure 7). Yamamoto s tartrate derived auxiliaries (15) based on the ether-directed cyclopropanation allowed the efficient preparation of cyclopropylcarboxaldehyde derivatives The reaction proceeded with high diastereocontrol, and the auxiliary could be cleaved under mild acidic conditions (equation 73). 

The cyclopropanation of a, (3-unsaturated carbonyls can be achieved using metal-free ylides. This is an attractive strategy avoiding the use of expensive metal-based catalysts and potentially hazardous diazo compounds. Two main approaches to the asymmetric ylide-mediated cyclopropanation have been developed, both utilising enantiopure amines as catalysts. 

TABLE 1. Cyclopropanation of a,/3-unsaturated carbonyl compounds with diazomethane... 

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See also in sourсe #XX -- [ ]

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