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From Blue Azulenes to Blue Heptalenes – New Strongly Polarized π ‐Convertible Heptalenes
Author(s) -
Landmesser Thomas,
Linden Anthony,
Hansen HansJürgen
Publication year - 2013
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.201300138
Subject(s) - malononitrile , chemistry , medicinal chemistry , yield (engineering) , pyridine , acceptor , dimethylformamide , stereochemistry , organic chemistry , catalysis , materials science , physics , solvent , metallurgy , condensed matter physics
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‐[(1 E )‐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‐[(1 E )‐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 CH 2 Cl 2 in the presence of TiCl 4 /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.