Divinylzinc

Enantioselective alkenylation was first reported by Oppolzer and Nadinov. Divinylzinc adds to aldehydes in the presence of the chiral diamino alcohol catalyst 37 with high enantioselectivity (>96% ) (equation 16)51. Alkenylzinc bromide adds to aldehydes in the presence of the lithium alkoxide of /V-methylephcdrinc (>98% )52. Ti-TADDOL is also an effective chiral catalyst in the addition of divinylzinc53. 

With regard to diorganozincs other than primary dialkylzincs, various diorganozincs such as divinylzinc (> 96% ee, addition to benzaldehyde),4 difurylzinc (72% ee, addition to benzaldehyde),5 diphenylzinc (78-82% ee, addition to various aldehydes),6 and diisopropylzinc (93% ee, addition to benzaldehyde)7 have been utilized in the chiral (3-aminoalcohol catalysed reactions. Alkenyl(alkyl)zincs4b,c and alkynyl(alkyl)zincs8 afford the corresponding chiral allylic and propargyl alcohols. 

Asymmetric addition of (CH1=CH)1Zn to aldehydes. The chiral tridendate ligand 1, derived from (+ )-camphor-10-sulfonic acid, effects highly enantioselective addition of R2Zn to aldehydes. Significantly, even divinylzinc adds to aryl and aliphatic aldehydes to furnish (R)-allylic alcohols in 82-96% ee. 

A multi-gram enantioselective synthesis of (+)-37, a key precursor to the tetracycline antibiotics, has been performed from simple heterocyclic compounds. Key steps in the route involve enantioselective addition of divinylzinc to 3-benzyloxy-5-isoxazolecarboxaldehyde (with 93% ee) for the preparation of 36 and, after its nucleophilic addition to 35, an intramolecular furan Diels-Alder cycloaddition <07OL3523>. 

Allylation of Aldehydes. Synthesis of enantiomerically pure allyl alcohols can be accomplished by catalytic asymmetric addition of divinylzinc to aldehydes using a camphorsulfonic acid-derived catalyst (eq 22). ... 

Grignard reagents - - have been used extensively to prepare alkylzinc halides (1 see equatirxi 5) and to s< ne extent to prepare dialkylzinc reagents not available by oxidative addition reactions, such as di-r-butylzinc or divinylzinc (see Scheme 4). Although moderate yields are often obtained, some optically active dialkylzinc reagents have been prepared in 49-81% yield. 

The enantioselective addition of organometallics to aldehydes is a useful approach to optically active secondary alcohols. Diorganozinc reagents add with excellent enantioselectivity to aldehydes in the presence of a chiral catalyst such as 1,2- or 1,3-amino alcohols (see equation 14 and Table 2). In most cases, diethylzinc has been used, but the reaction could be extended to some other dialkylzinc reagents and to divinylzinc. Alkylzinc halides afford secondary alcohols with a substantially lower enantiomeric excess. Many aldehydes are good substrates, "- but the best results are usually obtained with aromatic aldehydes. ... 

This method has been extended to the reaction of PhCsCZnBr with aldehydes in the presence of stoichiometric amounts of the lithium alcoholate of 1.14 (R = Me). Divinylzincs (RCH=CH)2Zn react under similar conditions, or also in the presence of other lithium alcoholates [650]. Under precise experimental conditions, PhMgBr adds to aliphatic or aromatic aldehydes in the presence of zinc salts and 1.14 (R = n-Bu). The enantiomeric excesses in these additions are higher than 75%. Diaiylzincs react with aldehydes in the presence of aminoalcohols bearing a ferrocene skeleton 2.47 with a very high enantioselectivity [651, 652], Schiff bases have also been used as catalysts in such reactions [367], as have some titanium complexes (see below) [559,653,654,655],... 

The synthesis began with the highly selective addition of divinylzinc to commercially available 2,3,5-tri-O-benzyl-D-arabinofuranose to provide hep-tenitol 27 in 95% yield. Benzoylation of 27 occurred on the less hindered hydroxyl group, leading mainly to the C-1 position protection (3.5 1 mixture). Standard Swem oxidation conditions then provided the desired 5-keto benzoate 28 (Scheme 2). 

Wooten A, Carroll PJ, Maestri AG, Walsh PJ (2006) Unprecedented alkene complex of zinc (II) structures and bonding of divinylzinc complexes. J Am Chem Soc 128 4624-4631... 

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