Categories: C-O Bond Formation, Synthesis of cyclic ethers >
Synthesis of epoxides
Key step in the synthesis of chiral phenyloxirane is the enantioselective catalytic reduction of an achiral chloromethyl ketone by means of a chiral oxazaborolidine as catalyst and borane as stoichiometric reductant.
E. J. Corey, S. Shibata, R. K. Bakshi, J. Org, Chem., 1988, 53, 2861-2863.
Dynamic kinetic resolution (DKR) of various aromatic chlorohydrins using Pseudomonas cepacia lipase (PS-C “Amano” II) and a ruthenium catalyst afforded chlorohydrin acetates in high yields and high enantiomeric excesses. These optically pure chlorohydrin acetates can be transformed to a wide range of important chiral compounds.
A. Träff, K. Bogár, M. Warner, J.-E. Bäckvall, Org. Lett., 2008, 10, 4807-4810.
The Mitsunobu cyclodehydration of chiral phenethane-1,2-diols, readily accessed from styrene derivatives, provides the corresponding styrene oxides with high levels of stereoretention for electron-poor substrates. The combination of tricyclohexylphosphine and diisopropylazodicarboxylate in THF provides the best results.
S. A. Weissman, K. Rossen, P. J. Reider, Org. Lett., 2001, 3, 2513-2513.
Acetylenic epoxides are directly prepared by nucleophilic ring closure of propargylic alkoxides generated by lithium acetylide addition to α-haloketones. A subsequent, mild and efficient cycloisomerization in the presence of InCl3 as catalyst delivers 2,3,5-trisubstituted furans.
J. Y. Kang, B. T. Connell, J. Org. Chem., 2011, 76, 2379-2383.
Alkynyl halides serve as a source of Br+ and acetylide ions in an efficient one-step preparation of alkynyl epoxides, important organic building blocks, from readily available starting materials.
A. Trofimov, N. Chernyak, V. Gevorgyan, J. Am. Chem. Soc., 2008, 130, 13538-13539.
The regioselective synthesis of several aminoepoxides has been achieved without observing any trace of azetidinols. The use of the mild supported base KF-Celite in refluxing acetonitrile is crucial for modulating the excellent regioselectivity observed.
V. Pace, P. Hoyos, J. V. Sinisterra, A. R. Alcántara, W. Holzer, Synlett, 2011, 1831-1834.
The aza-Payne rearrangement of 2,3-aziridin-1-ols under basic conditions gives epoxy amines. Subsequent nucleophilic attack of the epoxide by dimethylsulfoxonium methylide yields a bis-anion, which upon a 5-exo-tet ring-closure yields the desired pyrrolidine. This process takes place with complete transfer of stereochemical fidelity and can be applied to sterically hindered aziridinols.
J. M. Schomaker, S. Bhattacharjee, J. Yan, B. Borhan, J. Am. Chem. Soc., 2007, 129, 1996-2003.