Efficient Synthesis of Furan-2-ylacetates, 7-(Alkoxycarbonyl)benzofurans, and 7-(Alkoxycarbonyl)-2,3-dihydrobenzofurans Based on Cyclization Reactions of Free and Masked Dianions: A “Cyclization/Dehydrogenation” Strategy
作者:Esen Bellur、Peter Langer
DOI:10.1021/jo051767i
日期:2005.11.1
A variety of furan-2-ylacetates have been prepared by dehydrogenation of monocyclic 2-alkylidene-tetrahydrofurans, which are readily available by cyclizations of open-chained 1,3-dicarbonyl dianions with 1-bromo-2-chloroethane. 5'H-[2,3']Bifuranyl-2'-ones are available based on sequential "cyclization/dehydrogenation" reactions of alpha-acetyl-gamma-butyrolactones. A variety of 7-(alkoxycarbonyl)-benzofarans and 7-(alkoxycarbonyl)-2,3-dihydrobenzofurans were prepared by a cyclization/ dehydrogenation strategy. These reactions rely on cyclizations of 2-oxocycloalkane-1-carboxylate/derived 1,3-dicarbonyl dianions ("free dianions") or 1,3-bis-silyl enol ethers ("masked dianions") with various 1,2-dielectrophiles.
Regio- and Diastereoselective Synthesis of 2-Alkylidenetetrahydrofurans by Domino S<sub>N</sub>/S<sub>N</sub>‘ and S<sub>N</sub>/S<sub>N</sub> Reactions of 1,3-Dicarbonyl Dianions
作者:Peter Langer、Edith Holtz、Inass Karimé、Nehad N. R. Saleh
DOI:10.1021/jo010303r
日期:2001.9.1
The domino C,O-cyclodialkylation reaction of dilithiated 1,3.-dicarbonyl compounds with 1,4-dibromo-2-butene resulted in regio- and diastereoselective formation of 2-alkylidene-5-vinyltetrahydrofurans. The cyclization of 1,3-dicarbonyl dianions with 1-bromo-2-chloroethane regio- and diastereoselectively afforded 2-alkylidenetetrahydrofurans under thermodynamic reaction control.
Synthesis of (tetrahydrofuran-2-yl)acetates based on a ‘cyclization/hydrogenation/enzymatic kinetic resolution’ strategy
作者:Esen Bellur、Ilia Freifeld、Dominique Böttcher、Uwe T. Bornscheuer、Peter Langer
DOI:10.1016/j.tet.2006.03.077
日期:2006.7
A variety of (tetrahydrofuran-2-yl)acetates and (pyrrolidin-2-yl)acetates have been prepared by hydrogenation of 2-alkylidene-tetrahydrofurans and 2-alkylidenepyrrolidines, which are readily available by cyclization reactions of 1,3-dicarbonyl dianions (free dianions') or 1,3-bis-silyl enol ethers ('masked dianions') with 1,2-dielectrophiles. The enzymatic kinetic resolution of (tetrahydrofuran-2-yl)acetates with recombinant esterase Est56 proceeded with excellent enantioselectivities (E > 100). (c) 2006 Elsevier Ltd. All rights reserved.
Chemoselective, Regioselective, and <i>E</i>/<i>Z</i>-Diastereoselective Synthesis of 2-Alkylidenetetrahydrofurans by Sequential Reactions of Ambident Dianions and Monoanions
作者:Peter Langer、Esen Bellur
DOI:10.1021/jo034966f
日期:2003.12.1
A number of novel beta-ketoesters were prepared by regioselective alkylation reactions of simple beta-ketoester dianions. The cyclization of the dianions of these 1,3-dicarbonyl derivatives with 1-bromo-2-chloroethane afforded a variety of 2-alkylidenetetrahydrofurans with very good regioselectivity and E/Z-diastereoselectivity. These products were deprotonated to give novel ambident carbanions. The
Synthesis of Functionalized Furans Based on a ‘[3+2] Cyclization/Bromination/Elimination’ Strategy
作者:Peter Langer、Esen Bellur
DOI:10.1055/s-2006-926301
日期:——
The bromination of 2-alkylidenetetrahydrofurans -readily available via one-pot [3+2] cyclizations - afforded 2-alkylidene-3-bromotetrahydrofurans. Elimination of hydrogen bromide and subsequent aromatization of these compounds provided a convenient approach to functionalized furans.