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Reactions of 1,1‐bis(dimethylamino)‐1,3‐butadiene with olefins – (4 + 2) cycloadditions and zwitterion formation
Author(s) -
Sustman Reiner,
Rogge Monika,
Nüchter Ursula,
Bandmann Heinz
Publication year - 1992
Publication title -
chemische berichte
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 0009-2940
DOI - 10.1002/cber.19921250722
Subject(s) - zwitterion , chemistry , tetracyanoethylene , acrylonitrile , cycloaddition , medicinal chemistry , nitrile , acetonitrile , photochemistry , stereochemistry , molecule , organic chemistry , catalysis , polymer , copolymer
1,1‐Bis(dimethylamino)‐1,3‐butadiene ( 1 ) as a strong donor diene ( E 1/2 = 0.03 V vs. SCE, 1st IP v = 6.94 eV) is treated with acrylonitrile, dimethyl dicyanofumarate, and tetracyanoethylene. Cycloaddition with acrylonitrile is slow and requires elevated temperatures at which elimination of dimethylamine with formation of 1‐cyano‐2‐(dimethylamino)‐1,3‐cyclohexadiene occurs. The reaction of 1 with TCNE at −40°C in acetonitrile is very fast and leads to the zwitterion 5 . At T ⩾ −20°C, 5 eliminates hydrogen cyanide to give a highly colored (λ max = 489 nm, lgϵ = 4.716) merocyanine. A zwitterion 9 generated from 1 and dimethyl dicyanofumarate can be isolated in crystalline form. The structural analysis shows that the zwitterions are produced by attack of the olefin at the antiperiplanar conformation of 1 . Both zwitterions which can be trapped as crystalline picrates cannot be converted to cycloadducts. These results suggest that cycloaddition is observed if zwitterion formation becomes energetically unfavorable.