Ring-Opening Reactions of Oxabicyclic Alkene Compounds:  Enantioselective Hydride and Ethyl Additions Catalyzed by Group 4 Metals

Titanium and zirconium catalysts selectively catalyze either the ethyl or hydride addition to [2.2.1] 4,5-bis(methoxymethyl)-7-oxabicycloheptene (6); the ring-opened products formed depend on catalyst, temperature, alkylaluminum reagent, and the concentration of alkylaluminum. Bis(neoisomenthylinden...

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Bibliographic Details
Published in:Journal of organic chemistry 2000-06, Vol.65 (13), p.3902-3909
Main Authors: Millward, Dan B, Sammis, Glenn, Waymouth, Robert M
Format: Article
Language:English
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Summary:Titanium and zirconium catalysts selectively catalyze either the ethyl or hydride addition to [2.2.1] 4,5-bis(methoxymethyl)-7-oxabicycloheptene (6); the ring-opened products formed depend on catalyst, temperature, alkylaluminum reagent, and the concentration of alkylaluminum. Bis(neoisomenthylindenyl)zirconium dichloride catalyzes the ethyl addition ring-opening of 6 to produce (1R,2S,3S,6R)-2,3-bis(methoxymethyl)-6-ethylcyclohex-4-enol (7) in 96% ee. Zirconium catalysts catalyze the ring-opening of [3.2.1] 2,4-dimethyl-3-(benzyloxy)-8-oxabicyclo-6-octene (7) when ethylmagnesium bromide is used as a reagent. Both hydride and ethyl addition products are obtained at all conditions studied. Bis(neoisomenthylindenyl)zirconium dichloride catalyzes the ethyl addition ring-opening of 7 to produce (1S,2R,3S,4S,7S)-2,4-dimethyl-3-(benzyloxy)-7-ethyl-5-cyclohexen-1-ol (8) in 48% ee.
ISSN:0022-3263
1520-6904
DOI:10.1021/jo991429f