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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 β-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 α-propargyl β-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

In(OTf) 3 or In(NTf 2 ) 3 effectively catalyze the cyclo-isomerization reaction of a-propargyl-b-keto esters and their imineanalogues to afford trisubstituted furans and pyrroles, respectively.Both terminal and internal alkynes take part in the reaction withgood functional-group compatibility in the presence of only a smallamount of the catalyst. Key words: indium catalyst, keto ester, cyclization, furan, pyrrole The utility of indium reagents and catalysts has beenwidely proven by organic reactions involving carbonylgroups, 1 such as the Barbier reaction, 2 aldol reaction, 3 andHosomi–Sakurai reaction. 4 Indium can also activate C–Ctriple bonds to form new C–C bonds, because of its soft-ness, as reported by us 5 and others. 6 Formation of carbon–heteroatom bonds via activation of triple bonds has alsobeen reported. For instance, Tan et al. 7a described that 10mol% of InCl 3 promotes one-pot synthesis of furan deriv-atives via tandem reaction that involves intermolecularcondensation of a propargylic alcohol and a 1,3-dicarbon-yl compound, mainly 1,3-diketones, in refluxing chlo-robenzene. Herein we report that In(OTf)