A new class of chiral spirocyclic borate ligands 5a–d with a rigid borocycle has been developed. The catalyst formed from chromium(II)-5a promotes the highly efficient enantioselective Nozaki–Hiyama allylation of alkyl and aryl ketones using allyl bromide. The scope of the present method is shown to be wide, and it affords an efficient access to chiral tertiary homoallylic alcohols.
Asymmetric Allylboration of Ketones Catalyzed by Chiral Diols
作者:Sha Lou、Philip N. Moquist、Scott E. Schaus
DOI:10.1021/ja0651308
日期:2006.10.1
Chiral BINOL-derived diols catalyze the enantioselective asymmetricallylboration of ketones. The reaction requires 15 mol % of 3,3‘-Br2-BINOL as the catalyst and allyldiisopropoxyborane as the nucleophile. The reaction products are obtained in good yields (76−93%) and high enantiomeric ratios (95:5−99.5:0.5). High diastereoselectivities (dr ≥ 98:2) and enantioselectivities (er ≥ 98:2) are obtained
Rhodium-Catalyzed Kinetic Resolution of Tertiary Homoallyl Alcohols via Stereoselective Carbon−Carbon Bond Cleavage
作者:Ryo Shintani、Keishi Takatsu、Tamio Hayashi
DOI:10.1021/ol800120p
日期:2008.3.1
A nonenzymatic kinetic resolution of tertiary homoallyl alcohols has been developed through a rhodium-catalyzed retro-allylation reaction under simple conditions. Selectivity factors of up to 12 have been achieved by employing (R)-H8-binap as the ligand, and the reaction can be conducted on a preparative scale.
In the presence of enantiopure MTBH2
(monothiobinaphthol, 2-hydroxy-2â²mercapto-1,1â²-binaphthyl; 0.2 eq.) quantitative allylation of ArC(O)Me takes place with impure Sn(CH2CHCH2)4
(prepared from allyl chloride, air-oxidised magnesium and SnCl4) to yield tert-homoallylic alcohols in 85â92% ee. In the same process highly purified, or commercial, Sn(CH2CHCH2)4 yields material of only 35â50% ee. The origin of these effects is the presence of small amounts of the compounds, EtSn(CH2CHCH2)3, ClSn(CH2CHCH2)3 ClSnEt(CH2CHCH2)2 in the tetraallyltin sample and the presence of traces of water (which inhibits achiral background reactions). All the triallyl and diallyl species enhance the stereoselectivity in the catalytic allylation reaction, the chlorides more so than the ethyl compound. Hydrolysis of ClSnEt(CH2CHCH2)2 affords crystallographically characterised Sn4(μ3-O)(μ2-Cl)2Cl2Et4(CH2CHCH2)4. Reaction of this latter compound with MTBH2 leads to the most potent catalyst.
A Regio- and Enantioselective CuH-Catalyzed Ketone Allylation with Terminal Allenes
作者:Erica Y. Tsai、Richard Y. Liu、Yang Yang、Stephen L. Buchwald
DOI:10.1021/jacs.7b12271
日期:2018.2.14
We report a method for the highly enantioselective CuH-catalyzed allylation of ketones that employs terminalallenes as allylmetal surrogates. Ketones and allenes bearing diverse and sensitive functional groups are efficiently coupled with high stereoselectivity and exclusive branched regioselectivity. In stoichiometric experiments, each elementary step of the proposed hydrocupration-addition-metathesis