The Lewis acid mediated cyclization of epoxides with 1,3‐bis(trimethylsilyloxy)‐1,3‐butadienes, electroneutral equivalents of 1,3‐dicarbonyl dianions, results in the formation of 2‐alkylidenetetrahydrofurans with a great variety of substitution patterns and functional groups. This includes the synthesis of 2,3′‐bifuranylidenes and 7‐oxabicyclo[4.3.0]nonanes. The cyclization of dienes with functionalized epoxides containing base‐labile groups proceeds with good chemoselectivity. In all reactions, good regio‐ and E diastereoselectivities are observed. Based on the stereoselectivities observed for reactions of 1,2‐disubstituted epoxides, a working hypothesis for the mechanism of the reaction is suggested.
The reaction of amide and thioamide dianions with epibromohydrin resulted in regioselective formation of 5-(hydroxymethyl)pyrrolidin-2-ones (pyroglutaminols) and -thiones. The cyclization of the dianion of N-(2-tert-butylphenyl)acetamide with epibromohydrin afforded racemic axially chiral 1-(2-tert-butylphenyl)-5-(hydroxymethyl)pyrrolidin-2-one with high diastereoselectivity.
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Triflates. -The 1,3-bis-silyl enol ether (I) reacts with the 2-methoxypyrrolidine (II) to afford the expected condensation product (III) in the presence of Tms-O-Tf. Extension of the reaction to the dialkoxy derivatives (V) and (VII) results in formation of bicyclic 1,3-dicarbonyl compounds. -(ALBRECHT, U.; ARMBRUST, H.; LANGER*, P.; Synlett 2004, 1, 143-145; Inst. Chem. Biochem.,
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