Relationship between regioselective reduction of cyclic anhydrides and path of nucleophilic approach to the activated carbonyl function
✍ Scribed by Margaret M. Kayser; Peter Morand
- Publisher
- Elsevier Science
- Year
- 1979
- Tongue
- French
- Weight
- 186 KB
- Volume
- 20
- Category
- Article
- ISSN
- 0040-4039
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✦ Synopsis
It has been demonstrated that the reduction of a carbonyl function with LiAlH4 is catalyzed by Li+ cation 132 and that stereoselection is fixed from the first step in the mechanism, namely, association of Li+ cation with the oxygen atom of the carbonyl function3. The subsequent addition of AlH4nucleophile to the activated carbonyl function4 has been shown to proceed with strict stereochemical restraints 536 . It was theoretically predicted and experimentally con- firmed that the approach vector of a nucleophile is not perpendicular to the C-O bond but forms an angle of ca 110' with it (9. -* Baldwin7 suggested that the path of nucleophilic attack may be further restricted in amide or ester functions due to the shift from the s-tric position, as in ketone 2, to a position in space away from the hetero atom (2). H@ Taking into account the above restrictions we have been able to rationalize the regioselectivity observed in the metal hydride reduction of a number of cyclic anhydrides' and have also shown that a previously postulated mechanism involving both carbonyl groups sequentially must be incorrect. 2,2-Dimethylsuccinic anhydride and 2,2-diphenylsuccinic anhydride are both reduced in a highly regioselective manner at the carbonyl function adjacent to the fully substituted carbon atom. This was attributed to a combination of electronic and steric factors operating in the same direction. In this comnunication we report reduction of 2,2-dimethyl-3,3_diphenylsuccinic anhydride iand of 695 the results of metal hydride