Diazabicyclo[2.2.2]octane - DABCO

Abstract

(1) In 1972, Anthony Baylis and Melville Hillman2 described the reaction of an aldehyde with a broad spectrum of activated alkenes under the influence of DABCO (I). (Matrix Presented) (2) Drewes et al.3 reported the DABCO (I)-catalyzed intramolecular Baylis-Hillman reaction of the acrylate ester of salicylaldehyde to afford a crystalline coumarin salt as the major product being in evidence with the proposed mechanism. (Matrix Presented) (3) Chiral C2-symmetric 2,3-disubstituted DABCOs4 have been effectively utilized for the asymmetric Baylis-Hillman reaction between p-nitrobenzaldehyde and methyl vinyl ketone under high pressure (5-10 kbar) to obtain asymmetric induction up to 47% ee. (Matrix Presented) (4) Leahy et al.5 described the most impressive asymmetric Baylis-Hillman reaction using Oppolzer's sultam as chiral auxiliary and DABCO as catalyst to obtain the chiral dioxanone product in high enantiomeric purity (>99% ee). It is noteworthy that the sultam auxiliary was fortuitously cleaved by the addition of a second equivalent of aldehyde. (Matrix Presented) (5) We have recently reported the DABCO-catalyzed diastereoselective Baylis-Hillman reaction using sugar acrylate6,7 as chiral Michael acceptor and sugar aldehyde 8 as chiral electrophile to achieve moderate to good diastereoselectivides (5-86% de). (Matrix Presented) (6) Recently, Hu and co-workers9 have shown that the use of stoichiometric base catalyst I, in an aqueous medium, accelerates the Baylis-Hillman reaction. Moreover, the less reactive Michael acceptor acrylamide,10 which normally reacts only under high pressure, also undergoes Baylis-Hillman coupling with reactive electrophiles under these conditions. (Matrix Presented) (7) The Baylis-Hillman coupling of salicylaldehyde11,12 with various activated alkenes in the presence of I proceeds with regio-selective cyclization to afford the corresponding 3-substituted chromene derivatives. (Matrix Presented).