Cyclopropanes hydroxyl group directing effect

The landmark report by Winstein et al. (Scheme 3.6) on the powerful accelerating and directing effect of a proximal hydroxyl group would become one of the most critical in the development of the Simmons-Smith cyclopropanation reactions [11]. A clear syw directing effect is observed, implying coordination of the reagent to the alcohol before methylene transfer. This characteristic served as the basis of subsequent developments for stereocontrolled reactions with many classes of chiral allylic cycloalkenols and indirectly for chiral auxiliaries and catalysts. A full understanding of this phenomenon would not only be informative, but it would have practical applications in the rationalization of asymmetric catalytic reactions. 

The directive effect of allylic hydroxyl groups can be used in conjunction with chiral catalysts to achieve enantioselective cyclopropanation. The chiral ligand used is a boronate... 

The cyclopropanation is sensitive to steric effects, adding from the less-hindered face. Having a neighboring hydroxyl group will generally accelerate the reaction, and will direct the cyclopropanation syn to the hydroxyl group even into sterically congested alkenes. 

Simmons-Smith reaction. Asymmetric methylene transfer to allyl glycosides containing a free hydroxyl group at C-2 arises from its directing effect. Both /3-l-glucopyranosides and their a-o- analogs have been exploited for the access of chiral cyclopropanes. 

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