reagents. The effects of various reaction parameters and of the TADDOL ligand structure on the catalyticactivity and enantioselectivity were investigated. The absolute configuration of several fluorination products was assigned through correlation. Evidence for ionization of the catalyst complex by chloride dissociation, followed by generation of titanium beta-ketoenolates as key reaction intermediates
Bifunctional chiral thioureas have been successfully used as organocatalysts in enantioselectivefluorinations of β-ketoesters. The corresponding products could be obtained with good to excellent enantioselectivity in high yields by using N-fluorobisbenzenesulphonimide (NFSI) as fluorination reagent.
A novel pathway for the preparation of 3, 4-dihydro-2H-1λ6-benzo[e][1, 2]thiazine 1, 1-dioxides 3 via an orthomethyl lithiation/cyclization reaction of N-acyl-o-toluenesulfonamides 5 is reported. Readily available N-acyl-o-toluenesulfonamides 5 were treated with 2 eq of n-BuLi at -78°C-0°C to give the corresponding sultams 6 in moderate to good yields. The resulting sultams 6 were converted to saturated sultams 3, which can be considered as one carbon-extended homologues of the Oppolzer sultams 1, in high yields by hydrogenation. Studies on the scope and limitation of this annulation for the preparation of sultams are discussed. Demonstration of the feasibility of using the sultams 3 templates for an electorophilic fluorinating agent is also described.
N-Fluoro-3-ethyl-3-methyl-1,1-dioxo-2,3-dihydro-1H-1λ6-benzo[e]1,2-thiazin-4-one, a new and efficient agent for electrophilic fluorination of carbanions
作者:Yoshio Takeuchi、Zhaopeng Liu、Emiko Suzuki、Norio Shibata、Kenneth L Kirk
DOI:10.1016/s0022-1139(99)00028-7
日期:1999.7
N-Fluoro-3-ethyl-3-methyl-1,1-dioxo-2,3-dihydro-1H-1 lambda(6)-benzo[e]1,2-thiazin-4-one (1) was prepared in good yield by fluorination of the corresponding sultam (3) with FClO3. The sultam (3) was prepared from saccharin (2) in 3 steps. The N-fluorosultam (1), a very stable crystalline solid, was found to fluorinate carbanions readily in good to excellent yields. (C) 1999 Elsevier Science S.A. All rights reserved.