Asymmetric Bromoaminocyclization and Desymmetrization of Cyclohexa-1,4-dienes through Anion Phase-Transfer Catalysis

Abstract

The catalytic enantioselective desymmetrizing bromoaminocyclization of prochiral cyclohexa-1,4-dienes has been achieved by using chiral anion phase-transfer catalysis, providing a range of enantioenriched cis-3a-arylhydroindoles bearing an all-carbon quaternary stereocenter in good yields (up to 78%) and excellent enantioselectivities (up to 97% ee). Furthermore, the potential application of this methodology to natural product total synthesis was demonstrated by the asymmetric synthesis of (+)-Mesembrane.

New Trends in Asymmetric Phase Transfer Catalysis

“…The same approach has been applied to the desymmetrization of cyclohexa-1,4-dienes 93 to generate cis-aryloctahydroindoles 94 with one all carbon quaternary stereocenter in good yields and excellent enantioselectivities (Scheme 30). [62]…”

Iron porphyrin-catalysed C(sp3)–H amination with alkyl azides for the synthesis of complex nitrogen-containing compounds

“…Some of these alkaloids exhibit potent anticancer activity, 51 and their intriguing structures have been attracting the attention of organic chemists. [52][53][54] As shown in Scheme 3, azide 6 underwent intramolecular unactivated C(sp 3 )-H amination to afford 7 in 95% yield, from which (±)-mesembrane could be obtained according to the reported procedure. 55…”

Enantioselective halogenation via asymmetric phase‐transfer catalysis

“…The enantioselective bromoaminocyclization method was recently extended to a desymmetrization manifold by the groups of He and Deng (Scheme 27). 66 Under slightly modified Toste's conditions, meso ‐1,4‐cyclohexadienes with a pendant tosylamide were transformed to brominated cis ‐hydroindoles containing a quaternary stereocenter. The formation of small amounts of the 6‐ endo cyclization products accounted for the moderate yields.…”