Simmons-Smith cyclopropanation unsaturated ketones

The adduct (157) derived in>m (5)-(141) and an a,p-unsaturated ketone (156) undergoes Simmons-Smith cyclopropanation which is directed by the coexisting p-hydroxysulfoximine chiral center. As outlined in Scheme 36, this is a new methodology for optical activation of cyclopropyl ketones (159). Indeed, optically active tricyclic ketones (-)-(161) and (-f)-(161) were synthesiz firm a bicyclic ketone (160) in optical purities of 96% and 94%, respectively (equation 36). 

The excellent affinity of the alkylzinc reagent for ethereal oxygen in the Simmons-Smith cyclopropanation of allylic alcohols and ethers has been exploited for the asymmetric cyclopropanation of a, -unsaturated aldehydes and ketones using homochiral protecting groups. ... 

The reaction of Michael acceptors with dimethyloxosulfonium methanide has been extensively explored.3 4,111 112 115 In addition to carbene (or carbenoid) additions (Section 1.2.1.) and the Simmons-Smith method,114 (see also Section 1.2.1.1,) this is the most widely utilized method for the introduction of a cyclopropane ring, in good to excellent yield, to a,/J-unsaturated ketones,120- 126 esters118 120,122,128 - 130,132 amides,118,119 133 nitriles,1l8-119,126 isonit-... 

Scheme 6.26. Auxiliary-based asymmetric cyclopropanations (addition of CH2 ) of a, 3-unsaturated aldehydes and ketones, (a) [98] (b) [99,100] (c) [101-104] (d) Proposed transition structures [104]. Only one zinc and the transfer methylene are shown other atoms associated with the Simmons-Smith reagent are deleted for clarity.

Although the Simmons-Smith reaction has found considerable use in organic synthesis, it is not readily applicable to the formation of highly substituted cyclopropanes, since 1,1 -diiodoalkanes (other than diiodomethane) are not readily available. Substituted zinc carbenoids can be prepared from aryl or a,p-unsaturated aldehydes (or ketones) with zinc metal, and these species can be trapped with an alkene to give substituted cyclopropanes.The addition of chromium carbenes (see Section 1.2.2) to alkenes can be used to effect cyclopropanation to give substituted cyclopropanes. Thus, addition of excess 1-hexene to the chromium carbene 113 gave the cyclopropane 114 as a mixture of diastereomers, with the isomer 114 predominating (4.92). ... 

Easily accessible acetals and ketals of a,p-unsaturated aldehydes and ketones derived fi-om C2-symmetric chiral 1,2-diols have been successfully used with Simmons-Smith reagents furnishing cyclopropane aldehydes with high selectivity and recovery of the auxiliary. Thus, dialkyl tartrates proved to be superior compared to 1,2-diphenyl-ethanediols as chiral auxiliaries in reactions of a,p-unsaturated aldehydes. 

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