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A Spectroscopic Investigation of Donor‐Acceptor‐Substituted Heptalenes
Author(s) -
Ott Philipp,
Hansen HansJürgen
Publication year - 2001
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 - 10.1002/1522-2675(20010919)84:9<2670::aid-hlca2670>3.0.co;2-p
Subject(s) - chemistry , moiety , acceptor , substituent , stereochemistry , dimethylformamide , nitrobenzene , solvent , medicinal chemistry , crystallography , organic chemistry , catalysis , physics , condensed matter physics
It is shown that the heptalene‐4,5‐dicarboxylates 5 react with their Me group at C(1) with N , N ‐dimethylformamide dimethyl acetal or other acetals of this type in N , N ‐dimethylformamide (DMF) to give the corresponding 1‐[( E )‐2‐( N , N ‐dialkylamino)ethenyl]‐substituted heptalene‐4,5‐dicarboxylates 8a – 8e as well as 8k and 8i in good yields ( Table 1 ). In a similar manner, the 1‐[( E )‐2‐pyrrolidinoethenyl]‐substituted heptalene‐5‐carboxylates 8f – h were synthesized from the corresponding heptalene‐carboxylates 10 – 12 , carrying a CHO, CN, or ( E )‐2‐(methoxycarbonyl)ethenyl group at C(4) ( Table 1 ). All new heptalenes with the π ‐donor and π ‐acceptor groups at C(1) and C(4), respectively, exhibit a strongly enhanced heptalene band I in the spectral region of 450 – 500 nm in MeCN ( Table 7 and Figs. 4 – 7 ), whereby the specific position is dependent on the π ‐donor quality of the N , N ‐dialkylamino substituent at C(2′) and the π ‐acceptor property of the group at C(4). The position of heptalene band I is also strongly solvent‐dependent as is demonstrated in the case of heptalene 8i ( Table 9 ). A good linear correlation with the CT band of 1‐(diethylamino)‐4‐nitrobenzene or ( E )‐4‐(dimethylamino)‐ β ‐nitrostyrene ( Figs. 11 and 12 ) characterizes the heptalene band I also as an electronic CT transition. Irradiation into this band of 8i leads, as observed in other cases ( cf . [1]), to a double‐bond shift in the heptalene moiety (→ 8′i ; Figs. 8 – 10 ). On warming in solution, 8′i is converted quantitatively to 8i .