Search

A convenient synthetic protocol for diverse fused chromenes was successfully developed by a three-component reaction of alkyl isocyanides, dialkyl but-2-ynedioates, and various cyclic 1,3-dipolarophiles containing o-hydroxyphenyl group. In the absence of any catalyst, the three-component reaction of alkyl isocyanides, dialkyl but-2-ynedioates, and 3-(o-hydroxyarylidene)indolin-2-ones in tetrahydrofuran at 60 °C resulted in unique functionalized spiro[cyclobuta[c]chromene-1,3′-indolines] in good yields and with high diastereoselectivity. However, the similar three-component reaction with 2-(5-halo-2-hydroxyarylidene)indolin-2-ones afforded unexpected chain products in satisfactory yields. In addition, the three-component reaction of alkyl isocyanides, dialkyl but-2-ynedioates, and 2-(o-hydroxyarylidene)-1,3-indanediones in tetrahydrofuran at 60 °C resulted in complex indeno[2′,1′:5,6]pyrano[3,4-c]chromene derivatives in high yields and with high diastereoselectivity.

The domino reactions of 1,3-thiazolidinedione, malononitrile, and aromatic aldehydes in the presence of different organic amines were studied. Secondary amines such as pyrrolidine, piperidine, morpholine, and dimethylamine and primary amines such as benzylamine yield dihydrothiophene derivatives through a domino ring-opening/recyclization reaction of 1,3-thiazolidinedione. Bulky diethylamine, diisopropylamine, and 1,4-diazabicyclo[2.2.2]octane give spirocyclohexano-1,3-thiazole through a double Michael addition/spirocyclization reaction.

The domino reaction of alkyl and aryl isocyanides with two molecules of 2-arylidene-1,3-indanediones in acetonitrile at 80 °C resulted in unique functionalized spiro[dibenzo[a,f]azulene-6,2′-indenes] in good yields, in which the two 2-arylidene-1,3-indanediones acted as different building blocks to construct the polycyclic system. More importantly, the unprecedented anticipation of the ortho-position of benzylidene group to form a novel dibenzo[a,f]azulene ring through a formal [5 + 2] cycloaddition process was first observed. On the other hand, DABCO-promoted reaction of the isocyanides with two molecules of 2-arylidene-1,3-indanediones in acetonitrile at 80 °C afforded functionalized spiro[cyclopenta[a]-indene-2,2′-indene] derivatives.

Diverse functionalized dihydrobenzofuran spiro-indanedione-oxindole scaffolds were conveniently synthesized by base-promoted cyclization reaction of Morita–Baylis–Hillman (MBH) carbonates of isatins and 2-(o-hydroxybenzylidene)-1,3-indanediones. The two diastereomeric dispiro[indene-2,1′-cyclopenta[b]benzofuran-2′,3″’-indolines] could be selectively synthesized by using DABCO or DMAP as a base promoter. More importantly, DABCO or DMAP facilitated the annulation reaction of MBH formates of isatins and 2-(o-hydroxybenzylidene)-1,3-indanediones selectively, resulting in spiro[cyclopropa[c]chromene-1,2′-indene]-1′,3′-diones or dispiro[indene-2,1′-cyclopenta[b]benzofuran-2′,3″’-indolines]. Additionally, a similar reaction with MBH maleimides of isatins afforded dispiro[indene-2,5′-benzofuro[2′,3′:1,5]cyclopenta[1,2-c]pyrrole-4′,3″’-indolines] in high yields and with high diastereoselectivity.

Triethylamine promoted the pseudo-five-component reaction of aromatic aldehyde with four molecules of 1,3-indanediones in refluxing ethanol to give unique polycyclic bicyclo[2.2.2]octane derivatives containing bridged- and spiro-indanone scaffolds in good yields. The mechanistic studies supported that the reaction included base-catalyzed cyclotrimerization of 1,3-indanedione to give an active cyclic diene and the sequential Diels–Alder reaction with in situ generated 2-arylidene-1,3-indanediones as electron-deficient dienophiles. On the other hand, the pseudo-four-component reaction of salicylaldehyde with 1,3-indanedione afforded the dibenzo[b,g]indeno[1′,2′:3,4]fluoreno[1,2-d]oxonines in high yields. This reaction clearly demonstrated the high efficiency, molecular convergence, atom-economy, and impressive selectivity of multicomponent reactions.

p-TsOH-catalyzed cycloaddition of various 3-vinylindoles and (indol-2-yl)diphenylmethanols in acetonitrile gave the functionalized cyclopenta[b]indoles in good yields and with high diastereoselectivity via [3 + 2] cycloaddition reaction. More importantly, FeCl3-catalyzed annulation reaction afforded unexpected functionalized cyclohepta[1,2-b:4,5-b′]diindoles in satisfactory yields, in which a formal [4 + 3] cycloaddition and an unprecedented C3/C2 carbocation rearrangement were first confirmed by the determination of single-crystal structure.