Preparation of Enantiomerically Pure β‐Silylcarboxyl Derivatives by Asymmetric 1,4‐Addition to N‐Enoyl‐sultams. Preliminary Communication

Abstract

(28.V11.86) EtAIC1,-promoted additions of organocopper reagents to camphor-derived, conjugated N-enoyl-sultams gave saturated and olefinic P-silylcarboxyl derivatives with high diastereodifferentiation. Nondestructive removal of the chiral auxiliary followed by oxidative Si-C bond cleavage furnished enantiomerically pure acetate-derived aldols and propionate-derived 'unfi'-aldols (oirr silyl-directed a methylation).P-Silylcarbonyl compounds show significant promise in organic synthesis. Two features of the P-SiPhMe, substituent are particularly interesting: 1 j its topological bias on a-enolate protonation and methylation [l] as well as 2) its convertibility into a OH group with retention of configuration [2].In continuation of previous work on asymmetric and hydride additions [4] to conjugated N-acyl-sultams, we report here the first asymmetric synthesis of p-silylcarboxylates and their transformation into enantiomerically pure acetate-derived aldols and propionate-derived 'anti'-aldols. Furthermore, we describe the analogous -face-selective preparation of y,6-alkenyl-,8-silylcarboxyl derivatives which offer additional synthetic possibilities via SET -type allylsilane substitutions2).For reasons of versatility, it was advantageous to incorporate the silyl group into the prochiral substrate. The starting N-1/3-(silyl)enoyl]sultam 1 (R'=SiPhMe,, (Scheme was readily prepared by successive treatment of ( E j-3(dimethylphenylsilyl)acrylicPresented at the IASOC-11-Meeting, Ischia, May 1986. For an alternative approach to racemic and to enantiomcrically pure ~,fi-alkenyl-B-silylcarbonyl derivatives by Cluisen rearrangements see [ S ] ; for asymmetric syntheses of non-functionalized allylsilanes, see [6]; for revicws on stercospecific SE2'-type substitutions of allylsilanes, see [7]. All new compounds were characterized by IR, 'H-NMR (360 MHL), and mass spectra. This acid (m.p. 89-91") was prepared in analogy to 3-(trimethylsilyl)acrylic acid [8] by successive treatment of ( E l -1,2-bis(tributylstannyl)ethylene [9] at -78" with BuLi, CISiPhMc,, BuLi, and CO,. ')4,

Diastereoselective and enantioselective conjugate addition reactions utilizing α,β-unsaturated amides and lactams

“…Like the Mukaiyama example, the Oppolzer auxiliary ( 4 ) was used in DCA reactions with Grignard reagents [ 36 – 37 ]. The advantages of using this auxiliary are that it is readily available from (−) or (+)-camphor-10-sulfonyl chloride, both the starting N -enoyl sultam and the product from the DCA reaction can be purified by recrystallization, and the auxiliary is easily removed.…”

Grignard 1,4‐Additions to para‐Substituted (2R)‐N‐Cinnamoylbornane‐10,2‐sultam Derivatives: Revised Configuration for the N,OAc‐Keteneacetal Formation in the Presence of Cu(I)

“…In the latter case, the free nucleophile could eventually attack the opposite face, as usual. This could also explain the reverse selectivity observed in the presence of an excess of either LiCl or Cu(I) nonaggregating Lewis acids .…”

“… For 1,4‐vinyl cuprate additions systematically opposite to the N lp, whatever the adopted SO 2 /C=O syn or anti , C=O/C=C s‐ cis disposition, see . For similar 1,4‐additions of alkenylzirconocene chloride, see .…”

Metal-directed stereoselective functionalization of alkenes in organic synthesis

“…10 Protonation of the transient "enolates" 41 followed by crystallization yielded enantiomerically pure a,p-disubstituted carboxyl derivatives 42.…”