Aluminum-Catalyzed Enantio- and Diastereoselective Carbonyl Addition of Propargylsilanes. A New Approach to Enantioenriched Vinyl Epoxides
摘要:
A new pathway involving a Lewis acid-catalyzed carbonyl addition reaction of propargylsilanes and its subsequent development into a general enantio- and diastereoselective process are described. Aliphatic propargylsilanes with both saturated and unsaturated sidechains were effective nucleophiles affording highly functionalized chiral vinyl epoxides in good enantioselectivities (85-94% ee), excellent diastereoselectivities (> 99:1 E:Z; > 99:1 anti:syn) and in moderate to good yields (49-97%).
Catalytic Enantioselective Protoboration of Disubstituted Allenes. Access to Alkenylboron Compounds in High Enantiomeric Purity
作者:Hwanjong Jang、Byunghyuck Jung、Amir H. Hoveyda
DOI:10.1021/ol5022417
日期:2014.9.5
Proto-boryl additions to 1,1-disubstituted allenes in the presence of 1.0–5.0 mol % of chiral NHC–Cu complexes, B2(pin)2, and t-BuOH proceed to afford alkenyl–B(pin) products in up to 98% yield, >98:2 site selectivity, and 98:2 er. The enantiomerically enriched alkenylboron products can be converted to otherwise difficult-to-access alkenyl bromides, methylketones or carboxylic acids. What’s more,
1-Substituted allenylsilanes reacted with 3-alkoxycyclobutanones in the presence of TiCl4 to afford 8-oxabicyclo[3.2.1]octan-3-ones stereoselectively. Nucleophilic attack of allenylsilanes to a 1,4-zwitterionic intermediate formed from 3-alkoxycyclobutanones and TiCl4 followed by 1,2-silyl migration, five-membered cyclization with an alkoxy group, and seven-membered cyclization of titanium enolate
[reaction: see text] The catalytic, enantioselective [3 + 2] cycloaddition reaction of 1-alkyl-substituted allenylsilanes with alpha-imino ester has been achieved by means of [Cu(MeCN)(4)]BF(4)/(R)-DM-SEGPHOS catalyst to afford silyl-substituted dehydroproline derivatives in high yields and enantioselectivities.
Formal [3 + 2] and [3 + 3] Additions of Acceptor-Substituted Cyclopropylmethylsilanes to Allenylsilanes
作者:Veejendra K. Yadav、Vardhineedi Sriramurthy
DOI:10.1021/ol047991w
日期:2004.11.1
1,3-Dipolar synthons formed from vicinal TBDPS-substituted cyclopropyl alkyl/phenyl ketones on treatment with Lewis acids such as TiCl4 and Et2AlCl reacted with allenylsilanes to furnish [3 + 2] and [3 + 3] adducts with high regio- and stereocontrol.