The Preparation of Nonracemic Secondary α-(Carbamoyloxy)alkylzinc and Copper Reagents. A Versatile Approach to Enantioenriched Alcohols

Abstract

[reaction: see text] Chiral alpha-(carbamoyloxy)alkyllithium reagents, prepared using Hoppe's sBuLi/(-)-sparteine methodology, were transmetalated with ZnCl(2). Further transmetalation with CuCN with overall retention of configuration gave chiral species that reacted with various electrophiles to give enantiomerically pure alcohols after deprotection. A short, highly efficient synthesis of an industrially relevant pheromone, japonilure, illustrates the value of the methodology.

Asymmetric Deprotonation with Alkyllithium–(−)‐Sparteine

“…Benzylic and allylic halides lead to partial racemization 4 , presumably due to single-electron transfer (SET) in the alkylation step. As very recently found by Papillon and Taylor, racemization of 42 can be suppressed by copper-zinc-lithium exchange before alkylation 36 …”

“…The complex formed from s-BuLi/(−)-sparteine (11) 34 proved to be the most efficient base for asymmetric deprotonation at −78 • C. With substrates 21, having no further strongly complexing groups in the vicinity, usually the selection in favour of the pro-S-proton in complex 22 to form the epimer 23 is greater than 97:3, and occasionally ratios of 99:1 35,36 have been recorded (equation 6). 23 does not equilibrate below −40 • C with its diastereomer epi-23 and both can be trapped by electrophiles with strict stereoretention to yield the enantiomeric products 24/ent-24 with e.r.…”

Diethylzinc‐Mediated Allylation of Carbonyl Compounds Catalyzed by [(NHC)(PR3)PdX2] and [(NHC)Pd(η3‐allyl)Cl] Complexes

“…Elemental analyses were performed at the ICSN (microanalytical service). Compounds 14a, [35,36] 14b, [36] 17a, [7f] 17b, [7f,37] 17c, [7f,12g,38] 17d, [12g] 17f, [12g] 17h, [38] 17i, [39] 17j, [40] 17k, [12f] 17l, [41] 18k, [12f] 20c, [42] 20e, [43] 20f, [37] 20i, [43,44] 20j, [42,35b] and 20k [35b] have previously been described in the literature. 0.088 mmol).…”

Glucokinase Activator

“…3) Transmetalation with Zn on a chiral lithiated alkyl carbamate had been reported by Taylor via addition of a solution of ZnCl 2 to an in situ generated chiral organolithium (Scheme 8.10 ) [15] .…”