Azulenothiophene derivatives

Treatment of 2-(l,2-dibromoethenyl)quinoxalines 57 with Na2CS3 affords thieno[2,3- ]quinoxalines 59. Addition of the thiocarbonate to the side chain generates 58. Intramolecular cyclization of 58 with loss of CS2 and NaBr leads to 59 (Scheme 14) <2001J(P1)154>. Azulenothiophenes 61 are prepared from azulene derivatives 60 by the reaction with thioacetamide (Scheme 15) <2002H(58)405>. Similar reactions of furyl ketones 62 afford thieno[3,4-3]furans 63 <1998JHC71>. 

In acetovinyl derivative 54 (Scheme 56), the bond-length alternation (as it is known from parent azulenothiophene 45a) almost disappears this fact indicates a considerable contribution of the dipole resonance structure 233 (99TL6609). 

In early pioneer work, TNB adducts, picrates, and styphnates of Under- and artemazulene (2 and 8, respectively) have been described (39YZ162, 54CCC792,56JCS142), later on TNB derivatives and picrates of azulenothiophenes, for instance, 69 and 15 (60CIL1302, 67MI1, and respective further articles) and of azulenop3Fridines, for instance, 96a, 96b, and 98b (63BCJ633). 

Vilsmeier reactions (cf. 970R(49)1) of azulenothiophenes 45a/46 and 15 (Scheme 59) yield formyl derivatives 241a/241b (03OBC2572) and acetyl compound 242 (70BCJ509), respectively. Thiophene 171, which... 

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