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Anionic Cyclizations of Pentynones and Hexynones: Access to Furan and Pyran Derivatives
Author(s) -
Nicola Thomas,
Vieser Ralf,
Eberbach Wolfgang
Publication year - 2000
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/(sici)1099-0690(200002)2000:3<527::aid-ejoc527>3.0.co;2-n
Subject(s) - chemistry , furan , pyran , moiety , cyclohexenone , medicinal chemistry , methylene , alkyne , ketone , triple bond , yield (engineering) , stereochemistry , organic chemistry , double bond , catalysis , materials science , metallurgy
On treatment with base the pentynones 8a‐f undergo anionic addition reactions of the resulting enolate species to the alkyne moiety and afford the 2,5‐disubstituted furans 10a‐f in yields ranging from 10‐91%. The proposed mechanism involves the 2‐methylene‐dihydrofurans 11 as intermediates which tautomerize to yield the observed products. In the case of the α‐picolyl derivative 8g both possible enolates 12 and 13 are formed which are subsequently transformed to the products 10g and 14g , respectively. Starting with the hexynones 9a‐e an analogous reaction takes place with the formation of the pyran derivatives 15 and 16 in comparable yields. Under the same reaction conditions the n ‐butyl ketone 9f gives rise to two isomeric compounds, namely the 4 H ‐pyran 16f and the cyclohexenone 17 . This result is explained by assuming initial formation of two isomeric enolates which react either by O‐ or C ‐attack on the carbon‐carbon triple bond.