Solvent-free synthesis of naphthopyrans under ball-milling conditions

Under solvent-free ball-milling conditions, the nucleophilic addition reactions of terminal alkynes to carbonyl compounds promoted by KOH proceeded efficiently at ambient temperature. Subsequent cyclization reactions of the synthesized propargylic alcohols with 2-naphthol catalyzed by indium trichloride tetrahydrate, leading to the formation of naphthopyrans, were then investigated. In most cases, side reactions were avoided and thus high yields were achieved. (c) 2008 Elsevier Ltd. All rights reserved.