Benzofuran structure

The 2a,7b-dihydrocyclobuta[7>]benzofuran structure, obtained by addition of activated acetylenes to benzofurans (see Houben-Weyl, Vol.E6b, p 148), isomerizes thermally to a 1-benz-oxepin182 184 185 which reacts further to 1-naphthol derivatives at higher temperature182,185 (see Section 1.2 ). Under photochemical conditions, the 1-benzoxepins undergo ring contraction to the starting material.182 184... 

In the case of ferulic acid, dimers are known one of these has a difuran structure and another a benzofuran structure. 

Deguelin (19),32 in which rings D and E have a chromene, not a benzofuran, structure, is fully as ichthyotoxic and insecticidal as rotenone. It has been suggested33 that the toxophore in rotenoids might be the sequence =CH—CH=CH—O— in rings C and D, which is found both in (13) and in (19). The same sequence is found in... 

The difference between the heats of formation of C8HeO+ from reactions (10) and (11) (46 kcal) probably exceeds the uncertainties and errors mentioned above, which suggests that the fragment ion does not have a ground-state benzofuran structure (2). The close similarity (within experimental error) of the heats of formation in reactions (10) and (12), is consistent with the acetylenic-phenol structure (4) for the ion (Occolowitz and White, 1968) but this does not form proof of identity. The... 

Although many of the complex natural chromene, chroman, pyran and benzofuran structures clearly have arisen from reactive prenyl precursors which themselves have invariably not been isolated, certain prenyl derivatives of dihydric phenols have served as model compounds in cyclisation processes likely to be the pathways towards those naturally occurring compounds. 2-Prenylphenols and 2- and 4-prenylresorcinols and orcinols with C5, C o, and... 

Scheme 18.26 Natural products (a) and pharmaceutical agents (b) containing the benzofuran structural motif.

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