Regioselective Synthesis of Functionalized Furans by Cyclization of 1,3‐Bis‐Silyl Enol Ethers with 1‐Chloro‐2,2‐dimethoxyethane

Abstract

Cyclization of 1,3‐bis‐silyl enol ethers with 1‐chloro‐2,2‐dimethoxyethane allowed an efficient, regio‐ and diastereoselective synthesis of a variety of 2‐alkylidene‐4‐methoxytetrahydrofurans. The TFA‐mediated elimination of methanol resulted in the formation of functionalized furans. Similarly, 2,3,3a,4,5,6‐hexahydro‐2,3‐benzofurans were prepared and transformed into 4,5,6,7‐tetrahydro‐2,3‐benzofurans by treatment with TFA. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Gold catalysis: benzanellation versus alkylidenecyclopentenone synthesis

“…R f (PE/EA, 10:1)¼0. 16 3.08 (d, J¼14.8 Hz, 1H), 6.25 (ddd, J¼3.2, 0.9, 0.7 Hz, 1H), 6.35(dd, J¼3.2, 1.9 Hz, 1H), 7.38 (d, J¼1.9, 0.9 Hz, 1H). 13 15 To a solution of the alcohol 4c (1.79 g, 9.48 mmol) in DCM (60 mL) was added DMP (4.42 g, 10.4 mmol).…”

“…, 1H), 7.37 (d, J¼1.90 Hz, 0.90 Hz, 1H), 7.44-7.48 (m, 2H), 7.55-7.58 (m, 1H), 7.99-8.02 (m, 2H) 16. To a solution of ethynylmagnesium chloride (14.6 mL, 0.6 M solution in THF/toluene, 8.75 mmol) in THF (60 mL) was added a solution of 5c (858 mg, 4.61 mmol) in THF (30 mL).…”

Five‐Membered Heterocycles: Furan

“…a,b-Unsaturated carbonyl compounds with an appropriate leaving group undergo 1,5-electrocyclization reactions to yield 2,5-disubstituted furans upon heating in the presence of an acid, presumably through an intermediate formed from 1-oxapentadienyl cations, whose conformational and energy properties were also studied by DFT calculations (B3LYP/6-31 þ G Ã ) [83]. A 2,3-disubstituted furan, such as 88, with different functionalities has been synthesized through an acid-catalyzed elimination reaction of 2-alkylidenetetrahydrofuran 87, which can be prepared from the cyclization of 86 in high regioselectivity (Scheme 6.34) [84]. 2-Substituted furans and bicyclic furans can be synthesized by this methodology.…”

Catalyst-free cross-coupling of N-tosylhydrazones with chromium(0) Fischer carbene complexes: a new approach to diarylethanone

“…After purification by silica gel column chromatography, the product was isolated as a white solid (28.9 mg, 52% 2-(Furan-2-yl)-1-phenylethanone (3l). 18 The title compound was prepared via the general procedure. After purification by silica gel column chromatography, the product was isolated as a yellow oil (11.6 mg, 31%).…”