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[2 + 2] cycloaddition of optically active ketenes. Synthesis of (−)‐blastmycinone . Preliminary Communication
Author(s) -
Fráter Georg,
Müller Urs,
Günther Wulf
Publication year - 1986
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19860690813
Subject(s) - chemistry , cycloaddition , ether , adduct , optically active , stereochemistry , selectivity , transformation (genetics) , propenyl , sequence (biology) , medicinal chemistry , organic chemistry , catalysis , biochemistry , gene
[2 + 2] Cycloaddition of (menthyloxy)methylketene ( 2 ) to cis ‐ethyl propenyl ether showed a ca. 3:1 diastereo‐selectivity. A two‐step transformation of the thermodynamically more stable adduct 4 furnished the (2 R *, 3 R *)‐compound 5 with ca. 50% e.e. ( Scheme 1 ). The analogous reaction sequence with cis ‐ benzyl 1‐hexenyl ether ( 9 ) and 2 showed a ca. 5:1 diastereoselectivity in 10 and 11 ( Scheme 2 ). Absolute configuration of C(3) and C(4) in 11 has been proved by converting it to (−)‐blastmycinone. Accordingly, the preferred transition state has been deduced as 15 .