4,5-DIHYDROISOXAZOLE AND 4,5-DIHYDRO-1,2,4-OXADIAZOLE DERIVATIVES FROM CYCLOADDITION REACTIONS OF NITRILE OXIDES TO ALKYL N-(DIPHENYLMETHYLENE)-ALPHA,BETA-DEHYDROAMINO ACIDS

The alkyl N-(diphenylmethylene)-alpha,beta-dehydroamino acids 1 have been submitted to 1,3-dipolar cycloadditions with nitrile oxides. The reactivity of these compounds depends on the type and on the stereochemistry of the beta-substituents. With the unsubstituted terms 1a,b the reaction occurs on the C,C double bond, providing a good method for the synthesis of the 4,5-dihydroisoxazole derivatives 3a,b,c and for the gem-functionalized 4,5-dihydroisoxazoles amino carboxylic ester 5. The beta-substituted compounds 1c,d,e, inert to 1,1-dimethylethylnitrile oxide, undergo the reaction to the N,C double bond, thus giving with 2a,b the 4,5-dihydro-1,2,4-oxadiazole derivatives 4. All the reactions occur with high site- and regioselectivity.