Divergent Synthesis of Chromenoindoles and Spiroindolines via Domino Reaction of Indolyl-Substituted Isocyanides with Quinone Esters

Abstract

A dearomative spirocyclization of tryptamine-derived isocyanides with quinone esters is developed for the divergent synthesis of structurally complex chromeno[2,3-b]indole and polycyclic spiroindoline scaffolds. This domino reaction features the formation and conversion of the six-membered dihydropyran ring with an amendable N,O-aminal moiety.Letter pubs.acs.org/OrgLett

N-Heterocyclic Carbene-Catalyzed Remote Enantioselective C–C Bond Formation via 1,6-Addition with Formyl Enynes

“…In general, this three-step protocol proceeded smoothly to afford the target axially chiral compounds 6b to 6f in moderate to good yields and optical purities. It is worth noting that the obtained pyrano­[2,3- b ]­indole skeleton is one of the key structures in natural products and drug molecules (see Figure S1 in the Supporting Information for details) . Interestingly, the central-to-axial transfer process of compound 3r can also occur upon treatment of 3r with DDQ directly at room temperature.…”

Annulations involving p-benzoquinones: stereoselective synthesis of fused, spiro and bridged molecules

“…delivered the corresponding spiro products in moderate to good yields (42-74%); however, indoles containing Br, CHO, or CN at the 3-position did not participate A catalyst-free, sequential dearomative spiro-coupling of tryptamine-derived isocyanides with quinone resulting complex spiroindolines via a two-step one-pot method was investigated by Xu and Tang. 95 Spirochromenes are frequently found in natural products and employed as useful synthons in synthetic organic chemistry. 97 98 In this transformation, the benzoquinone moiety served as an effective C3-synthon.…”

“…A catalyst-free, sequential dearomative spiro-coupling of tryptamine-derived isocyanides with quinone resulting complex spiroindolines via a two-step one-pot method was investigated by Xu and Tang. 95 This domino reaction involved the construction and conversion of the six-membered dihydropyran ring 103 with an amendable N , O -aminal moiety. In the first step, the reaction of tryptamine-derived isocyanides 102 with quinone ester 101 produces chromenoindoles 103 .…”

Catalyst-Free Synthesis of Polycyclic Spiroindolines by Cascade Reaction of 3-(2-Isocyanoethyl)indoles with 1-Sulfonyl-1,2,3-triazoles

“…The [6,5,5,5]-tetracyclic spiroindolines were obtained when various electrophiles were employed, which were exemplified by utilizing Michael acceptors, ,, imines, and isocyanates (Scheme B, b). However, only four examples of the generation of [6,5,5,6]-tetracyclic systems were reported through the reactions with diazoacetates, aziridines, nitrile oxide, and quinones (Scheme B, c). On the basis of our continuous interest in N -heterocycle synthesis, herein, we report a novel spirocyclization of 3-(2-isocyanoethyl)­indoles with 1-sulfonyl-1,2,3-triazoles for the efficient catalyst-free synthesis of α-carboline containing a [6,5,5,6] ring skeleton (Scheme B, d).…”