Reversal of diastereofacial selectivity in the nucleophilic addition reaction to chiral N-sulfinimine and application to the synthesis of indrizidine 223AB
Diastereoselective addition reaction of ester enolates and Grignard reagents to optically active N-sulfinimines was examined. Reversal of the diastereofacialselectivity was realized by using appropriate metal species, solvents and additives, and the β-amino esters (up to >98% de) and the homoallylic amines (up to >98% de) were obtained in good yields. β-Amino esters thus obtained were converted to
Enantioselective preparation of 3,4,5-trisubstituted-4,5-dihydroisoxazoles and 4-substituted-5,6-dihydro-4H-[1,2]-oxazines by nitrile oxide cycloaddition to α-silyl allyl alcohols
Regio- and stereoselective 1,3-dipolar cycloaddition of nitrile oxide to opticallyactive α-silyl allyl alcohol provides a useful preparation of 3,4,5-trisubstituted 4,5-dihydroisoxazoles, which are readily converted into chiral 4-substituted 5,6-dihydro-4H-[1,2]-oxazines in 73–100% yields on treatment with TBAF.