Synthetic Strategy for Multisubstituted Fused Furan Compounds Using Main-Group Metal Reagents

In this account, we summarize our recent studies on the synthesis of multisubstituted furan compounds. The synthetic strategy relies on the electrophilic cyclization of o-hydroxy(alkynyl)arenes by using main-group metal reagents. For example, zinc salts have been found to mediate the cyclization of o-alkynylphenols to form thermally stable yet chemically reactive beta-zincio intermediates ('synthetic modules') that serve as platforms for the syntheses of a series of analogues having the same core structural motif (the 'molecular library'). This modular approach is applicable to the synthesis of new benzofurans and benzodifurans and their homologues, and allows us to study the photophysical and semiconducting properties of these products systematically. We have similarly developed a synthesis of benzotrifurans by a cesium hydroxide-mediated tandem SNAr/triple-cyclization reaction, as well as a synthesis of trisubstituted furans by indium-catalyzed cycloisomerization of alpha-propargyl beta-keto esters. 1 Introduction 2 Modular Approach for the Synthesis of Fused Furan Derivatives Using Zinc Salt 2.1 Zinc-Mediated Cyclization Reaction and Synthesis of Functionalized Benzofurans 2.2 Selective Syntheses of Benzodifurans Based on the Modular Method 2.3 Homologues of BDF: Naphtho- (NDF) and Anthradifurans (ADF) 3. Syntheses of Other Furans 3.1 Cesium Hydroxide-Promoted One-Pot Reaction for the Synthesis of Benzotrifurans 3.2 Indium-Catalyzed Cycloisomerization Reaction for the Synthesis of Multisubstituted Furans 4 Conclusions