Sünnemann HW, Hofmeister A, Magull J, de Meijere A. An Efficient Access to Novel Enantiomerically Pure Steroidal δ-Amino Acids.
Chemistry 2006;
12:8336-44. [PMID:
16991188 DOI:
10.1002/chem.200601076]
[Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
A highly chemoselective sequence of Stille and Heck couplings on the heterocyclic bromoenol triflates 2 a-c with the bicycloalkenylstannanes cis-3 and trans-3 furnished the intermediate bromobutadienes 4 a-c in good yields ranging from 73-94 %. A modified Heck coupling protocol employing the palladacycle 8 and an additional bidentate ligand such as 1,4-bis(diphenylphosphinyl)butane allowed a significant reduction in catalyst loading while still obtaining the heterocyclic 1,3,5-hexatrienes 5 a-c in good yields (71-94 %). The unsymmetrically substituted 1,3,5-hexatrienes 5 a-c in solution underwent 6pi-electrocyclizations following an optimized microwave-heating protocol to yield the steroidal tetracycles cis-7 a-c and trans-7 b (59-69 %). Tetracycles cis-7 a-c are the products of a subsequent 1,5-hydrogen shift to the thermodynamically more stable, more highly substituted diene units. Removal of the tert-butyl groups provided the novel steroidal delta-amino acid 9 a and the delta-amino acid derivatives 9 b, c in good yields (76-86 %).
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