Unexpected Tandem Reaction of New Type Morita-Baylis-Hillman Adducts Promoted by [Hmim]HSO4/NaNO3 System

Abstract

A tandem reaction of new type Baylis-Hillman adducts 1 was prompted by ionic liquid [Hmim]HSO4/NaNO3 system and the unexpected products 6-aryl-2H-pyran-3-carboxylates 2 and imidazolium salts 3 were efficiently formed via the rearrangement and substitution reaction. While mediated by [Emim]HSO4/NaNO3 system, the key intermediates 4 were isolated. A plausible mechanism for the transformation was given. INTRODUCTION Tandem reactions are of great importance in organic synthesis due to generation of some important products in a single operation with high atom economy and bond-forming efficiency. Recently, more and more novel types of tandem reactions, including tandem Michael addition, substitution, cyclization and rearrangement reaction, were extensively applied to organic synthesis, especially the synthesis of natural optically active products and heterocyclic compounds. The Baylis-Hillman reaction is a synthetically useful method for carbon-carbon bond-forming reactions to yield functionalized allylic alcohols, thereby providing handles for further manipulation in a multitude of synthetic organic transformations. In continuation of our research on new type Baylis-Hillman adducts 1 prepared from aryl methyl ketones via a combination of the Vilsmeier and the Baylis-Hillman reactions, we investigated the tandem reaction of new type Baylis-Hillman adduct 1 under the [Hmim]HSO4/NaNO3 system (Scheme 1). To our surprise, the unexpected products 6-aryl-2H-pyran-3-carboxylates 2 and/or imidazolium salt 3 were isolated. HETEROCYCLES, Vol. 85, No. 1, 2012 43