Journal
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
Volume 123, Issue 2, Pages 315-321Publisher
AMER CHEMICAL SOC
DOI: 10.1021/ja002662u
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- NIGMS NIH HHS [GM-18874] Funding Source: Medline
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A series of selected bicyclic carbamates in which the range of accessible angles and distances between the carbonyl group and the proton removed in an a-lithiation reaction are structurally defined have been investigated. Oxazolidinones 7-10 undergo stereoselective lithiation-substitution reactions to provide cis-18-27 and cis-31-35 as the major diastereomers. Two series of competition experiments show that the conformationally restricted carbamates 7, 10, 11, and 15 undergo lithiation via complexes more efficiently than Boc amines 4-6. These results along with semiempirical calculations suggest that a small dihedral angle and a calculated distance of 2.78 Angstrom between the carbamate carbonyl oxygen and the proton to be removed are favorable for a carbamate-directed lithiation. A series of tin-lithium exchange experiments on cis- and trans-18 and (S)-39 indicate that the configurational stability of a carbamate-stabilized organolithium species may be enhanced by restrictive geometry.
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