Simmons-Smith cyclopropanation, olefins application

A number of enantioselective Simmons-Smith-type cyclopropanations have been disclosed, of which three classic examples are discussed in this section [19]. In the first, Charette described the use of a dioxaborolane (111, Scheme 15.13) as an effective chiral controller group [68]. The presence of the basic amide C=0 was found to be critical for directing the cyclopropanation reagent to a single olefin diastereoface. Treatment of allylic alcohols such as 110 with 111 and Zn(CH2l)2 led to the formation of intermediate boronates that subsequently underwent cyclopropanation with excellent yields and enantioselectivities. An impressive iterative application of this method was showcased by Charette in a total synthesis of the natural product U-1065305 (113), a cholesterol transferase inhibitor [69]. 

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