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From blue Azulenes to blue Heptalenes - new strongly polarized π-convertible heptalenes


Landmesser, Thomas; Linden, Anthony; Hansen, Hans-Jürgen (2013). From blue Azulenes to blue Heptalenes - new strongly polarized π-convertible heptalenes. Helvetica Chimica Acta, 96(10):1851-1893.

Abstract

The 1,5,6,8,10-pentamethylheptalene-4-carboxaldehyde (4b) (together with its double-bond-shifted (DBS) isomer 4a) and methyl 4-formyl-1,6,8,10-tetramethylheptalene-5-carboxylate (15b) were synthesized (Schemes 3 and 7, resp.). Aminoethenylation of 4a/4b with N,N-dimethylformamide dimethyl acetal (=1,1-dimethoxy-N,N-dimethylmethanamine=DMFDMA) led in DMF to 1-[(1E)-2-(dimethylamino)ethenyl]-5,6,8,10-tetramethylheptalene-2-carboxaldehyde (18a; Scheme 9), whereas the stronger aminoethenylation agent N,N,N′,N′,N″,N″-hexamethylmethanetriamine (=tris(dimethylamino)methane=TDMAM) gave an almost 1 : 1 mixture of 18a and 1-[(1E)-2-(dimethylamino)ethenyl]-5,6,8,10-tetramethylheptalene-4-carboxaldehyde (20b; Scheme 11). Carboxylate 15b delivered with DMFDMA on heating in DMF the expected aminoethenylation product 19b (Scheme 10). The aminoethenylated heptalenecarboxaldehydes were treated with malononitrile in CH2Cl2 in the presence of TiCl4/pyridine to yield the corresponding malononitrile derivatives 23b, 24b, and 26a (Schemes 13 and 14). The photochemically induced DBS process of the heptalenecarboxaldehydes as ‘soft’ merocyanines and their malononitrile derivatives as ‘strong’ merocyanines of almost zwitterionic nature were studied in detail (Figs. 10–29) with the result that 1,4-donor/acceptor substituted heptalenes are cleaner switchable than 1,2-donor/acceptor-substituted heptalenes.

Abstract

The 1,5,6,8,10-pentamethylheptalene-4-carboxaldehyde (4b) (together with its double-bond-shifted (DBS) isomer 4a) and methyl 4-formyl-1,6,8,10-tetramethylheptalene-5-carboxylate (15b) were synthesized (Schemes 3 and 7, resp.). Aminoethenylation of 4a/4b with N,N-dimethylformamide dimethyl acetal (=1,1-dimethoxy-N,N-dimethylmethanamine=DMFDMA) led in DMF to 1-[(1E)-2-(dimethylamino)ethenyl]-5,6,8,10-tetramethylheptalene-2-carboxaldehyde (18a; Scheme 9), whereas the stronger aminoethenylation agent N,N,N′,N′,N″,N″-hexamethylmethanetriamine (=tris(dimethylamino)methane=TDMAM) gave an almost 1 : 1 mixture of 18a and 1-[(1E)-2-(dimethylamino)ethenyl]-5,6,8,10-tetramethylheptalene-4-carboxaldehyde (20b; Scheme 11). Carboxylate 15b delivered with DMFDMA on heating in DMF the expected aminoethenylation product 19b (Scheme 10). The aminoethenylated heptalenecarboxaldehydes were treated with malononitrile in CH2Cl2 in the presence of TiCl4/pyridine to yield the corresponding malononitrile derivatives 23b, 24b, and 26a (Schemes 13 and 14). The photochemically induced DBS process of the heptalenecarboxaldehydes as ‘soft’ merocyanines and their malononitrile derivatives as ‘strong’ merocyanines of almost zwitterionic nature were studied in detail (Figs. 10–29) with the result that 1,4-donor/acceptor substituted heptalenes are cleaner switchable than 1,2-donor/acceptor-substituted heptalenes.

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Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Department of Chemistry
Dewey Decimal Classification:540 Chemistry
Language:English
Date:2013
Deposited On:16 Dec 2013 13:50
Last Modified:05 Apr 2016 17:15
Publisher:Wiley-Blackwell
ISSN:0018-019X
Funders:Swiss National Science Foundation
Publisher DOI:https://doi.org/10.1002/hlca.201300138

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