Asymmetric alpha-substitution versus aza Diels-Alder reaction of electron deficient N-sulfonyl imines

Several N-arylsulfonylglycine esters have been brominated under photolytic conditions to provide the corresponding alpha-bromoglycine. These bromo est ers can be treated with a range of bases to generate N-sulfonyl imino ester s in situ; attempts to isolate the imines in a pure state were universally unsuccessful. Once generated, the imines can be trapped with cyclopentadien e to provide the corresponding aza Diels-Alder adducts in varying yields, d epending upon the base used. In addition, if organometallic bases were empl oyed (alkyllithiums and alkylaluminium reagents), not only were aza Diels-A lder adducts formed, but addition to the imine was also observed. In the ca se of organoaluminium reagents, imine addition was the major product. This process could be transformed into a stoichiometric asymmetric version, by g enerating a chiral aluminium reagent in situ to form a trialkyl (or trialko xy) aluminium reagent, which when reacted with an N-sulfonyl bromoglycinate resulted in 19 to 62% enantiomeric excess of the corresponding substituted glycinate product.