Enantioselective Binaphthophosphepine‐Promoted [3+2] Annulations of N‐Ts‐ and N‐DPP‐Imines with Allenoates and 2‐Butynoates

Abstract

The use of binaphthophosphepine 1a as a catalyst for the [3+2] cyclisation between allenoates or 2-butynoates and imines was investigated. The effects of the imine protecting group on both the catalytic activity and enantioselectivity were determined by comparing the behaviour of N-tosyland N-DPP-imines. The N-DPP-imines displayed lower reac-

Studies on the asymmetric, phosphine-promoted [3+2] annulations of allenic esters with 2-aryl-1,1-dicyanoalkenes

“…The same phosphine had been described previously to furnish high enantiomeric excesses in [3+2] cyclizations between allenoates and either enones 6b or imines, 16 as well as in [4+2] cyclizations on imines. 4 To further investigate the scope of the asymmetric cyclization methodology involving Binepine (S)-4 as the catalyst, we examined the possibility of using olefins with either esters or cyano and ester groups as electron-withdrawing functions (Scheme 3).…”

Organocatalytic transformations of alkynals, alkynones, propriolates, and related electron-deficient alkynes

“…Moreover, the experimental conditions were very mild and the reaction times were very short. 104 The yields were good or moderate but lower than ones obtained from Ntosylimines. That was due to partial decomposition during the isolation by column chromatography.…”

“…The authors also studied the reaction of both N-DPP (208) 104 and N-tosylimines (202), 105 catalyzed by a chiral phosphine derivative 210 (Scheme 90). The reported data demonstrated that the N-DPP group afforded higher enantiomeric excesses than the Ntosyl group; however the yields were higher with the latter one.…”

Stable synthetic equivalents of N-unsubstituted imines: Part 1. Synthesis

“…The aliphatic derivatives are not stable; as a rule, they are involved in the reaction without puri fication. The standard procedure for the removal of the Dpp fragment is acid solvolysis (a) on heating in concentrated HCl [60], (b) at ambient temperature in aqueous alcoholic solution of HCl [62,63], or (c) by treatment with gaseous HCl [61]. Yields vary from moderate to high.…”