Iodine-catalyzed aromatization of tetrahydrocarbazoles and its utility in the synthesis of glycozoline and murrayafoline A: a combined experimental and computational investigation

Abstract

A new protocol for the aromatization of tetrahydrocarbazoles has been achieved using a catalytic amount of iodine, giving high yields. The role of iodine in the aromatization has been explained by DFT, and its wide scope is extended to the total synthesis of glycozoline and murrayafoline A. This method has proven to be tolerant of a broad range of functional groups.

I2‐Catalyzed Total Synthesis of Collective 7‐Oxygenated Carbazole Alkaloids: Clauszoline‐K, ‐L, Clausine‐M, ‐N and Formal Synthesis of Siamenol

“…Alternatively, the compound 3 a was treated with molecular iodine (25 mol %) in DMSO at 80 o C; the corresponding aromatized product 7 was afforded with 94 % yield. More interestingly, this type of result was found to be our previous report …”

Enantioselective synthesis of functionalised tetrahydrocarbazoles via an organocatalysed Diels–Alder/ene reaction strategy

“…The solution was cooled to 0 o C before 4-phenyl-3H-1,2,4-triazole-3,5(4H)-dione (35 mg 6,173.9,154.5,153.6,152.1,136.2,131.6,131.0,129.3,128.5,126.7,125.7,125.6,125.4,123.5,119.4,113.9,47.2,39.9,38.3,28.0,27.1,25.2;IR(neat): υ max /cm -1 3255, 3080, 2932, 1693MS (pNSI) 5,10,10b-tetrahydropyrrolo[3,4-a]carbazole-1,3(2H,3aH)-dione…”

“…5 The tetrahydrocarbazoles have also been shown to be useful intermediates for the synthesis of carbazoles via iodine mediated oxidation. 6 A number of enantioselective routes to the tetrahydrocarbazoles have been reported, involving both transition-metal 7 and organocatalyzed 8 approaches. A recurring feature in synthetic approaches to both racemic 9 and enantioenriched 8(a,c,d,g,h,j-l) tetrahydrocarbazoles is the use a vinyl-indole, as a formal diene, in a Diels-Alder (D-A) type reaction.…”

Short synthesis of carbazole alkaloids: Ekeberginine, murrayaquinone A, and glycozoline

“…Synthesis of glycozoline (3) was an accidental outcome of a planned synthesis of a carbazole alkaloid murrayanine (11) from 3-methyl carbazole (10) as shown in retrosynthetic analysis in Scheme 3. Carbazole 10 was synthesized from 4-methyl cyclohexanone and phenyl hydrazine using reported [14] procedure.…”