B(C6F5)3-catalyzed Wolff rearrangement/[2 + 2] and [4 + 2] cascade cyclization of α-diazoketones with imines

Abstract

B(C₆F₅)₃ is shown to catalyze the reactions of carbonyl imines with α-diazoketones by initiating a Wolff rearrangement followed by a subsequent cyclization. However, variations in the N-protecting groups of imines alter the nature of the product. In the case of the B(C₆F₅)₃ mediated reaction of N-tert-butoxycarbonyl imines with α-diazoketones, [2 + 2] cascade rearrangement/cyclizations affording 20 β-lactams in yields up to 94%. In contrast use of N-benzoyl imines with α-diazoketones, [4 + 2] cyclizations afforded 14 oxazinone derivatives. These reactions were also performed on a gram-scale.