Metallierte Stickstoff‐Derivate der Kohlensäure in der organischen Synthese, XXVII. – Homoaldol‐Reaktion, VII. Lithiierung acyclischerN,N‐Dialkylcarbamidsäure‐2‐alkenylester; Silylierung und γ‐selektive α‐Hydroxyalkylierung von Homoenolat‐Reagenzien

Asymmetric Deprotonation with Alkyllithium–(−)‐Sparteine

“…As was found in 1980 by Hoppe and coworkers, a N,N-diisopropylcarbamoyloxy group in allylic position not only facilitates the deprotonation reaction by n-BuLi/TMEDA, but also enhances the chemical stability of the lithium compounds 54,208,209,217 …”

“…(a) Introduction of a strongly complexing substituent X such as N,N-dialkylcarbamoyloxy by Hoppe and coworkers 208,209 and N-(alkoxycarbonyl)amino groups by Beak and coworkers 30 …”

Asymmetric Homoaldol Reactions with Cyclohex‐2‐enyl N,N‐Diisopropylcarbamate: Kinetic Resolution, Elucidation of the Stereochemical Course and Applications in the Synthesis of Hexahydroisobenzofuran‐4‐(1H)‐ones

“…A solution of cyclohex-2-enol (4, 981 mg, 10 mmol) in THF (1 mL) was added to the stirred suspension by syringe and stirring was continued for 1 h at room temperature. N,N-Diisopropylcarbamoyl chloride [23] (6, 2.29 g, 14 mmol, 1.4 equiv.) was added over a period of 5 min and the reaction mixture was heated to reflux (90°C) for 11-13 h. After complete consumption of the starting material (TLC) the solution was cooled to room temperature and treated with aq.…”

Enantioselective γ‐Deprotonation of Alkyl‐Substituted O‐1,3‐Butadien‐2‐yl Carbamates and Regioselective Asymmetric Homoaldol Reaction

“…After carbamoylation of the commercially available crotyl alcohol 6a followed by complete isomerization of the allyl carbamate 7a via lithiation, lithium-titanium exchange, [7] and protonation, the 1-butenyl carbamate 8a was obtained in a total yield of 86 % and a Z:E ratio Ͼ 98:2 (Scheme 2). [8] The allyl alcohol 6b was synthesized starting from isobutyraldehyde by a Horner-Wittig-Emmons olefination and reduction of the resulting ester. [9] Carbamoylation of 6b and isomerization according to the same procedure as described for 8a afforded the 3-methylbut-1-enyl carbamate 8b in 76 % yield and a Z:E ratio Ͼ 98:2 (Scheme 2).…”