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Phosphine‐Catalyzed [4+2] Annulations of 2‐Alkylallenoates and Olefins: Synthesis of Multisubstituted Cyclohexenes
Author(s) -
Tran Yang S.,
Martin Tioga J.,
Kwon Ohyun
Publication year - 2011
Publication title -
chemistry – an asian journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.18
H-Index - 106
eISSN - 1861-471X
pISSN - 1861-4728
DOI - 10.1002/asia.201100190
Subject(s) - synthon , regioselectivity , alkyl , phosphine , chemistry , phosphonium , olefin fiber , catalysis , allene , ylide , annulation , dihydropyran , medicinal chemistry , organic chemistry
From our investigations on phosphine‐catalyzed [4+2] annulations between α‐alkyl allenoates and activated olefins for the synthesis of cyclohexenes, we discovered a hexamethylphosphorous triamide (HMPT)‐catalyzed [4+2] reaction between α‐alkyl allenoates 1 and arylidene malonates or arylidene cyanoacetates 2 that provides highly functionalized cyclohexenes 3 and 4 in synthetically useful yields (30–89 %), with moderate to exclusive regioselectivity, and reasonable diastereoselectivity. Interestingly, the [4+2] annulations between the α‐alkyl allenoates 1 and the olefins 2 manifested a polarity inversion of the 1,4‐dipole synthon 1 , depending on the structure of the olefin, thus providing cyclohexenes 3 exclusively when using arylidene cyanoacetates. The polarity inversion of α‐alkyl allenoates from a 1,4‐dipole A to B under phosphine catalysis can be explained by an equilibrium between the phosphonium dienolate C and the phosphorous ylide D .