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Diels ‐ Alder Approach to Highly Functionalized Tertiary α‐Hydroxy Ketones: A Novel Route to the Hexahydrobenzofuran Portion of the Avermectins and Milbemycins
Author(s) -
Ireland Robert E.,
Obrecht Daniel M.
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.19860690602
Subject(s) - chemistry , enone , diketone , ketone , bicyclic molecule , adduct , intramolecular force , diels–alder reaction , stereoselectivity , michael reaction , stereochemistry , medicinal chemistry , organic chemistry , catalysis
Abstract A highly regio‐ and stereoselective Diels ‐ Alder reaction between dienophiles of type I and dienes of type II ( Scheme 1 ) gives rise to Diels ‐ Alder adducts of type III . Upon treatment with BF 3 .Et 2 O, these adducts are smoothly converted into the corresponding enones ( Scheme 6 ). Under mild acidic conditions, enone (±)‐ 33 gave bicyclic diketone (±)‐ 34 via an intramolecular Michael ‐type addition. Diketone (±)‐ 34 has the correct relative configuration and a suitable ketone function at C(6) for further conversion into the hexahydrobenzofuran portion of the avermectins and milbemycins.