Diels-Alder cyclizations of N-acyl imines derived from glyoxylates 5 and 8 stereoselectively produced cis-fused bicyclo-1,3-dihydrooxazine γ-lactones 7 and 10, respectively. The cycloaddition failed to yield the corresponding δ-lactone 12 derived from precursor 11. Selective ring cleavages of cycloadduct 2 afforded hydroxy amide 13 and α-amino lactone 14. Efficient application of this methodology to the stereoselective synthesis of the N-terminal amino acid portion 15 of nikkomycin B (16) is described. Diels-Alder precursor 21, readily available in three steps from known allylic chloride 17, was cyclized to the bicyclodihydrooxazine 22. This compound was readily converted to lactone 26.
All Science Journal Classification (ASJC) codes
- Organic Chemistry