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(Salen)chromium Complex Mediated Asymmetric Ring Opening of meso ‐ and Racemic Epoxides with Different Fluoride Sources
Author(s) -
Haufe Günter,
Bruns Stefan
Publication year - 2002
Publication title -
advanced synthesis and catalysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.541
H-Index - 155
eISSN - 1615-4169
pISSN - 1615-4150
DOI - 10.1002/1615-4169(200202)344:2<165::aid-adsc165>3.0.co;2-1
Subject(s) - chemistry , cyclohexene oxide , cyclopentene , medicinal chemistry , enantiomeric excess , ether , epoxide , enantiopure drug , cycloheptene , organic chemistry , polymer chemistry , enantioselective synthesis , catalysis
The asymmetric ring opening of five meso‐ and three racemic epoxides with different fluorinating reagents in the presence of stoichiometric or slightly sub‐stoichiometric amounts of Jacobsen's enantiopure (salen)chromium chloride complex A gave the corresponding optically active vicinal fluorohydrins. Silver fluoride was used as one of the fluoride sources either in the presence of Bu 4 N + H 2 F 3 − in diethyl ether or in acetonitrile. The latter reactions starting from cyclohexene oxide ( 1 ) showed maximum 72% ee in the formed fluorohydrin 2 isolated in 90% yield. From other meso ‐epoxides such as cyclopentene oxide and cycloheptene oxide the corresponding fluorohydrins were isolated in 80% and 82% yield with 65% and 62% ee, respectively. In case of ring opening under similar conditions of the racemic styrene oxide or phenyl glycidyl ether 83% and 75% of the fluorohydrins with fluorine in the primary position were isolated with 74% ee and 65% ee, respectively. Tetrahydronaphthalene oxide yielded a 2:1 mixture of trans ‐ (23% ee) and cis ‐2‐fluoro‐3,4‐benzocyclohexenol (2% ee) suggesting competing S N 2 and S N 1 type ring openings. Other epoxides such as cyclooctene oxide, cis ‐stilbene oxide and α‐methylstyrene oxide did not react or gave the fluorohydrins with very small enantiomeric excess.