Convenient Synthetic Protocols for Diverse Functionalized Dihydrobenzofuran-Fused Spiro-indanedione-oxindole Scaffolds

Abstract

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)-1,3indanediones. 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.

Regioselective and Diastereoselective Construction of Diverse Dispiro-Indanone-Fluorenone-Oxindole Motifs

“…For explaining the formation of various polycyclic spiro compounds, a possible mechanism was briefly proposed in Scheme on the previously reported works and the present experimental results. First, the nucleophilic substitution of Lewis base DABCO or triethylamine to MBH carbonate of isatin 3 at the α-position through the S N 2′ reaction gave the electrophilic ammonium salt (A), leaving the BocO group as carbon dioxide and a tert -butoxide ion.…”

“…In these reactions, bindone actually acted as both 3C and 4C building blocks for the convenient construction of the privileged carbocyclic systems. In order to exploit the fruitful chemistry of reactive bindone and in continuation of our aim to develop efficient cycloaddition reactions for indanone-containing compounds, − we have investigated the base-promoted annulation reaction of bindone with various MBH carbonates of isatins. It is interesting to find that this annulation reaction showed high regioselectivity, diastereoselectivity, and molecular diversity (eq 4 in Scheme ).…”

Construction of Unique Spiro[dibenzo[a,f]azulene-6,2′-indenes] via Unprecedented Annulation of ortho-C–H Bond of Benzylidene Group

“…The structural analysis of the compound 3a clearly indicated that two molecules of 3-benzylidene-1,3-indanediones were introduced in the final product with one motif of 1,3-indanedione to form a fused cyclic system and another motif of 1,3-indanedione to exist on spiro position. The most unusual feature of spiro­[dibenzo­[ a,f ]­azulene-6,2′-indene] 3a is that the ortho-position of one phenyl group anticipated to form the benzo­[ a , f ]­azulene ring, which was not observed in the previously reported reactions of 2-arylidene-1,3-indanediones. − A literature survey showed that 1,3-indanedione usually underwent ring-opening process of the cyclopentyl ring to give a scaffold of benzocyclohexane-1,4-dione in many cycloaddition reactions, where the phenyl group remained as a substituted group in the formed carbocyclic or heterocyclic ring. On the other hand, the cyclohexyl isocyanide converted to the N -cyclohexylcarboxamide unit in the final product, which clearly indicated that cyclohexyl isocyanide is not incorporated in the seven-membered azulene ring in the domino reaction.…”

“…Therefore, 1,3-indanediones and 2-arylidene-1,3-indanediones were widely employed in many Michael addition, Diels–Alder reaction, cyclization, and domino reactions. , We have successfully revealed several efficient synthetic protocols for versatile spiro and fused cyclic compounds by domino reactions of 1,3-indanedione or the in situ generated 2-arylidene-1,3-indanediones . In these works, we found that 1,3-indanediones showed versatile reactivity and high molecular diversity . Prompted by the aforementioned background and as a further development of the domino reaction, we have investigated the domino reaction of alkyl isocyanides and 2-arylidene-1,3-indanediones.…”