Diastereoselective Cyclopropanations with Carbenoids Generated from Diazoalkanes

2 Diastereoselective Cyclopropanations with Carbenoids Generated from Diazoalkanes 

Derivatives of the Oppolzer sultam [32] may be employed in a general, chiral auxiliary-based approach to stereoselective synthesis of substituted cyclopropanes. In this context, Hacksell carried out a study in which unsaturated substrates such as 30 were converted into the corresponding cyclopro- 

Another chiral auxiliary-based approach was documented by Davies (Equation 5) [8, 34]. These studies involved diazo compounds that incorporate vinyl and C=0 substitution and revealed that these stable carbene precursors participate in a variety of useful transformations, including diastereoselective cydopropanations. Importantly, Davies found that the cydopropanations with 33, in contrast with those of their simpler diazoacetate counterparts, are highly diastereoselective. The reaction with styrene and chiral diazo compound 33 is representative treatment of styrene with 33 in the presence of a simple Rh catalyst resulted in the formation of product 34 with high asymmetric induction dr 98.5 1.5) and in 84% yield. In this example, the panto-lactone auxiliaiy is a convenient, readily available chiral alcohol. 

A number of features of this chiral auxiliary warrant further mention. Significantly, the use of this auxiliary was predicated on the fact that the ensu- 

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