Transformations of Modified Morita-Baylis-Hillman Adducts from Isatins Catalyzed by Lewis Bases

Abstract

The development of synthetic protocols to access architectures with broad structural and functional diversity from readily available starting materials is very attractive in both organic and medicinal chemistry fields. Toward this objective, the multifunctional isatin-derived Morita-Baylis-Hillman (MBH) adducts provide opportunities to construct a variety of complex scaffolds containing a "privileged" oxindole motif through several catalytic pathways. By forming the ammonium or phosphonium salts with Lewis bases, isatin-derived MBH adducts can undergo allylic substitutions with a range of nucleophiles, usually in a S_N 2'-S_N 2' pattern. Besides, assisted by Brønsted bases, the corresponding onium salts can be converted into the allylic ylide intermediates, which can undergo various annulation reactions or even 1,3-difunctionalizations. Moreover, recent cooperative catalysis of Lewis bases and transition metal complexes further puts forward the application of isatin-derived MBH adducts. This tutorial review covers the significant transformations of isatin-derived MBH adducts, mostly in an asymmetric version, catalyzed by various Lewis bases over the past decade.

Keywords: Lewis base; Morita-Baylis-Hillman adduct; allylic alkylation; annulation; isatin.