Ah ighly regioselective and stereoselective 1,5addition of alkyl groupst oe nantioenriched donor-acceptor cyclopropanes 1 and bicyclic cyclopropanes such as 6aryl-1-methoxycarbonyl-3-oxabicyclo[3.1.0]hexan-2-ones 4 using aG rignard reagentw ith ac atalytic amounto f Cu(OTf) 2 (0.1 equivalent) afforded optically active diesters 2 or trans-a,b-disubstituted g-butyrolactones 5 with an excellent level of stereoinduction. An excesso ft he Grignard reagent is necessary to perform the 1,5-alkylation with high yields.I nt he reactiono ft he enantioenrichedb icyclic lactone 4,ahighly stereoselective 1,5-addition and subsequent highly trans-selective protonation of the magnesium enolate via keto-enol isomerization furnished the trans-a,b-disubstituted-g-lactones with three contiguous chiral centers with excellent enantioselectivity. Based on the results, we also proposed the mechanism through cluster ion pairs or as imple ion pairt or ationalize the high stereoselectivity of the reaction.Supportinginformation for this article can be found under http:// dx.

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The addition of alcohols, phenols, and carboxylic acid to optically active cyclopropanes provides the title butyrolactones with excellent diastereoselectivity.