Highly Enantioselective [3+2] Coupling of Indoles with Quinone Monoimines Promoted by a Chiral Phosphoric Acid

Abstract

Highly enantioselective [3+2] coupling of 3-substituted indoles with quinone monoimines promoted by a chiral phosphoric acid has been reported. A large variety of benzofuroindolines were prepared in moderate to good yields (up to 98 %) with generally excellent enantioselectivities (up to 99 % ee).

Eight‐Step Total Synthesis of Phalarine by Bioinspired Oxidative Coupling of Indole and Phenol

“…After obtaining the optimized reaction conditions and suitable protecting group of indole,the scope of this reaction was examined with respect to the phenols and indoles ( Table 2). Unexpectedly,a ll of them gave better regioselectivity than that of p-methoxyphenol (8a), in which the p-phenoxyphenol, phenol, and p-NHTFA-phenol gave the corresponding 9p, 9q,a nd 9w as the sole products, respectively.T he indoles (11)(12)(13)(14)(15)(16)(17)(18)f used with five and sevenmembered rings as well as with different substituents at C2/ C3/C5 were then examined. Unexpectedly,a ll of them gave better regioselectivity than that of p-methoxyphenol (8a), in which the p-phenoxyphenol, phenol, and p-NHTFA-phenol gave the corresponding 9p, 9q,a nd 9w as the sole products, respectively.T he indoles (11)(12)(13)(14)(15)(16)(17)(18)f used with five and sevenmembered rings as well as with different substituents at C2/ C3/C5 were then examined.…”

Recent Developments in the Synthesis of Chiral Compounds with Quaternary Centers by Organocatalytic Cascade Reactions

“…In 2014, Zhang et al. reported a highly enantioselective [3+2] coupling of 3‐substituted indoles 183 with quinone monoimines 184 promoted by a chiral phosphoric acid 181 (Scheme ) . A variety of benzofuroindolines 185 were synthesized through this transformation.…”

Synthesis of 3-arylated indolines from dearomatization of indoles

“…44 The same year, the same authors implemented this process to the enantioselective [3+2] coupling of 3-substituted indoles 152 with quinone monoimine 153 with chiral phosphoric acid 12c as catalyst and high enantiomeric excess of benzofuroindolines 154 were obtained. (Scheme 24) 45 Very shortly after the work of Zhang, Shi reported the closely related enantioselective synthesis of 3-aryl indolines 156 and 158 by arylative dearomatization of indoles 152 with p-quinone imine ketals 155 catalyzed by the same chiral phosphoric acid 12c. 46 In contrast to the zinc triflate catalysis with 150b, the regioselectivity of the 1,4-addition to the quinone imine derivatives 153 is inverted with phosphoric acids, presumably due to different modes of activation of imine quinone derivatives.…”