Selective Generation of Free Radicals from Epoxides Using a Transition-Metal Radical. A Powerful New Tool for Organic Synthesis
作者:T. V. RajanBabu、William A. Nugent
DOI:10.1021/ja00082a021
日期:1994.2
halogens provides a route to functionalized cyclopentanes and other useful products. The radical initially formed from an epoxide can also be trapped by H-atom donors such as 1,4- cyclohexadiene or tert-butyl thiol, resulting in an overall reduction of the epoxide. In the absence of a H-atom donor or an olefin, this radical is trapped by Ti(", resulting in a fl-oxido-Ti organometallic species which undergoes
The pheromone (S)-(-)-frontalin (1) was synthesized in five steps in 94% ee via a chemoenzymatic route. In the key step, 2-methyl-2-(pent-4-enyl)oxirane [(±)-7a] was resolved employing lyophilized cells of Rhodococcus equi IFO 3730 (E=39).
信息素(S)-(-)-前腺素(1)通过化学酶法路线在五个步骤中合成,得到的对映体纯度为94%。关键步骤中,采用冷冻干燥的耐盐芽孢杆菌 R. equi IFO 3730 (E=39) 对2-甲基-2-(戊-4-烯基)环氧化物[(±)-7a]进行了分离。
Transition-metal-centered radicals in organic synthesis. Titanium(III)-induced cyclization of epoxy olefins
作者:William A. Nugent、T. V. RajanBabu
DOI:10.1021/ja00233a051
日期:1988.12
allows the direct synthesis of functionalized cyclopentane derivatives. This new reaction is based on an analogy to the extremely facilerearrangement of cyclopropylmethyl radical to homoallyl radical (eq 2). A a-complex of an epoxide with a paramagnetic transition metal4 having a half-filled (*-symmetry) d orbital represents an electronic analogue of the cyclopropylmethyl moiety. By analogy to eq 2, release
Chemoenzymatic deracemization of (±)-2,2-disubstituted oxiranes
作者:Romano V.A. Orru、Sandra F. Mayer、Wolfgang Kroutil、Kurt Faber
DOI:10.1016/s0040-4020(97)10338-6
日期:1998.1
The preparation of vicinal diets in up to 98% e.e. and 98% yield from the corresponding (+/-)-2,2-disubstituted epoxides was achieved via an enantioconvergent two-step hydrolysis: Thus, enantioselective enzymatic hydrolysis of the (S)-epoxide proceeded with retention of configuration furnishing the corresponding (S)-diol. In a subsequent step, the remaining (R)-oxirane was hydrolyzed during workup under acid catalysis with complete inversion of configuration yielding the (S)-diol. A detailed study of the latter reaction revealed that the experimental conditions have to be carefully chosen with respect to (i) nature of the acid, (ii) the solvent, and (iii) its water content to avoid racemization. (C) 1997 Elsevier Science Ltd. All rights reserved.
NUGENT, WILLIAM A.;RAJANBABU, T. V., J. AMER. CHEM. SOC., 110,(1988) N5, C. 8561-8562