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An Improved and Simplified Synthesis of 4‐Styrylazulenes
Author(s) -
Song Jianfeng,
Hansen HansJürgen
Publication year - 1999
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/(sici)1522-2675(19990310)82:3<309::aid-hlca309>3.0.co;2-h
Subject(s) - chemistry , tetrahydrofuran , trifluoroacetic acid , azulene , formylation , silica gel , medicinal chemistry , organic chemistry , catalysis , solvent
It is shown that 4‐ or 8‐[( E )‐styryl]‐substituted azulenes can easily be prepared from 4‐ or 8‐methylazulenes in the presence of potassium tert ‐butoxide ( t ‐BuOK) with the corresponding benzaldehydes in tetrahydrofuran (THF) at −5 to 25° (see Schemes 1 and 2 ). 6‐( tert ‐Butyl)‐4,8‐dimethylazulene ( 5 ) with both Me groups in reactive positions leads to the formation of a mixture of the mono‐ and distyryl‐substituted azulenes 6 and 7 , respectively ( Scheme 3 ). Vilsmeier formylation of 6 results in the formation of 3 : 2 mixture of the azulene‐carbaldehydes 8a and 8b , which can be separated by chromatography on silica gel. Reduction of 8a and 8b with NaBH 4 in trifluoroacetic acid (TFA)/CH 2 Cl 2 gives the 1‐methyl forms 9a and 9b , respectively, in good yields ( Scheme 4 ). The latter two azulenes are not separable on silica gel.