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β‐Cleavage of Bis(homoallylic) Potassium Alkoxides. Two‐Step Preparation of Propenyl Ketones from Carboxylic Esters. Synthesis of ar ‐Turmerone, α‐Damascone, β‐Damascone, and β‐Damascenone
Author(s) -
Snowden Roger L.,
Linder Simon M.,
Muller Bernard L.,
SchulteElte Karl H.
Publication year - 1987
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.19870700721
Subject(s) - chemistry , propenyl , potassium , cleavage (geology) , organic chemistry , medicinal chemistry , geotechnical engineering , fracture (geology) , engineering
The transformation of 36 bis(homoallylic) alcohols VII to alkenones IX and X via β‐cleavage of their potassium alkoxides VIIa in HMPA has been investigated ( cf. Scheme 2 ). These studies have established an order of β‐cleavage for 2‐propenyl, 1‐methyl‐2propenyl, 2‐methyl‐2‐propenyl, 1,1‐dimethyl‐2propenyl, and benzyl groups in alkoxides 49a – 56a and have allowed a comparison between the β‐cleavege reaction and the oxy‐ Cope rearrangement in alkoxides 74a – 83a . As illustrative syntheti applications, a two‐step preparatio of propenyl ketones 15 – 42 from carboxylic esters is described, together with syntheses of ar ‐turmerone ( 48 ), α‐damascone (( E )‐ 71 ), β‐damascone (( E )‐ 109 ), and β‐damascenone (( E )‐ 111 ).