Simple and efficient access to N-tosyl beta-amino ketones and their conversion into 2,4-disubstituted azetidines.

Treatment of N-tosylaldimines with acetophenone at room temperature in the presence of BF(3).OEt(2) as a catalyst furnished the corresponding N-tosyl beta-amino ketones in high yields (77-86%) within 6-9 h. Subsequent reduction and cyclization of these compounds afforded 2,4-disubstituted N-tosylazetidines, comprising a three-step, high-yielding synthesis starting from aldimines.