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Eine neue 2‐Allylphenol‐Cumaran‐Umlagerung
Author(s) -
Schmid E.,
Fráter Gy.,
Hansen H.J.,
Schmid H.
Publication year - 1972
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.19720550526
Subject(s) - chemistry , aryl , benzene , phenols , medicinal chemistry , yield (engineering) , organic chemistry , alkyl , materials science , metallurgy
2‐(1′‐Arylallyl)‐phenols ( 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 ) are transformed on heating in N, N‐diethylaniline at 225° into trans ‐2‐aryl‐3‐methyl‐coumarans ( 26 , 29 , 32 , 34 , 36 , 38 , 40 , 42 ) in excellent yields. The corresponding cis ‐coumarans are minor products. Similar thermal behaviour is shown by 2‐(1′‐vinylallyl)‐phenols ( 7 , 8 ) which are thermally converted into trans ‐3‐methyl‐2‐vinyl‐coumarans ( 24 , 19 ) and 5‐methyl‐2,5‐dihydro‐(1‐benzoxepins) ( 25 , 18 ). The latter compounds are thermally unstable and rearrange to give approximatively 3:1 mixtures of trans ‐ and cis ‐3‐methyl‐2‐vinyl‐coumarans ( 24 , 19 ). Reaction mechanisms for these new thermal rearrangements are discussed in schemes 2, 3 and 4. The 2‐(1′‐arylallyl)‐phenols 9 , 12 and 14 yield under acidic conditions (HBr/HOAc) the expected 3‐aryl‐2‐methyl‐coumarans 28 , 35 , 39 along with 2‐aryl‐3‐methyl‐coumarans 26 , 34 , 38 and 2‐aryl‐2‐methyl‐coumarans 44 , 45 , 46 . The intervention of phenonium ions is discussed for these reactions (cf. scheme 5). When the 2‐(1′‐arylallyl)‐phenols 12 and 14 were irradiated in benzene solution with a mercury high pressure lamp, the main products obtained were 3‐aryl‐2‐methyl‐coumarans 35 and 39 which were formed rapidly. 2‐Aryl‐3‐methyl‐coumarans yield also 3‐aryl‐2‐methyl‐coumarans, when irradiated in benzene solution.