Carbolithiation of Cinnamyldialkylamines. Stereochemistry of the Li to Zn Transmetalation and Configurational Stability of Benzylic Organozinc Halides

Enantioconvergent Fukuyama Cross‐Coupling of Racemic Benzylic Organozinc Reagents

“…Studies have shown that under ambient conditions,chiral cyclic and acyclicorganozinc halides appear to be configurationally stable, [14] however, secondary benzylic organozinc halides have been found to racemize more rapidly. [10,15] Thes econd concern was the selection of an appropriate chiral ligand, which does not only select preferentially one of the two enantiomers of the organozinc reagent, but also enforces af ast reductive elimination (whilst suppressing deleterious b-hydride elimination) to prevent any racemization of the key alkylpalladium species. [16] We started our investigations with the cross-coupling of as imple thioester substrate, 1a,w ith (1-phenylethyl)zinc Scheme 1.…”

Preparation and Reactivity of Acyclic Chiral Allylzinc Species by a Zinc‐Brook Rearrangement

“…[2] However,ifone could create stereogenic centers in acyclic systems,not through aclassical S N 2reaction between ac hiral electrophile and an achiral nucleophile (Scheme 1, path A), but rather through the reaction of ac hiral nucleophile (that would be used as an ew chiral building block for stereoselective synthesis) with an achiral electrophile,i tw ould broaden the synthetic possibilities in organic synthesis (Scheme 1, path B). [4,5] More recent developments have shown that few main-group organometallic species,s uch as organomagnesium [6] and organolithium, [7] as well as transition-metal species,s uch as alkylcopper [8] and alkylzinc, [9] present some configurational stability under particular circumstances (Scheme 1, path C). [3] To fulfill the requirements of configurational stability for secondary carbanions (R 1 ¼ 6 R 2 = alkyl, A)m etalloids such as organoboronates were intensively investigated.…”

Enantioconvergent Fukuyama Cross‐Coupling of Racemic Benzylic Organozinc Reagents

“…Our first concern was that the rate of racemization of the organozinc reagent should be fast enough to achieve an effective DKR. Studies have shown that under ambient conditions, chiral cyclic and acyclic organozinc halides appear to be configurationally stable, however, secondary benzylic organozinc halides have been found to racemize more rapidly . The second concern was the selection of an appropriate chiral ligand, which does not only select preferentially one of the two enantiomers of the organozinc reagent, but also enforces a fast reductive elimination (whilst suppressing deleterious β‐hydride elimination) to prevent any racemization of the key alkylpalladium species…”