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.
Highly Enantioselective Syntheses of Homopropargylic Alcohols and Dihydrofurans Catalyzed by a Bis(oxazolinyl)pyridine−Scandium Triflate Complex
作者:David A. Evans、Zachary K. Sweeney、Tomislav Rovis、Jason S. Tedrow
DOI:10.1021/ja011983i
日期:2001.12.1
Lewisacid promoted reactions of allylsilanes and allenylsilanes provide access to important building blocks for natural product synthesis. 1 For example, trimethylsilylallenes function as propargylic anion equivalents in aldehydeadditionreactions (eq 1, Path A).2 If the silicon center is sterically congested, the normal addition pathway is suppressed and functionalized dihydrofurans are produced