3 research outputs found
Synthesis and characterization of new Heptalenes with extended Ï-systems attached to them
Methyl heptalenecarboxylates of type A and B with Ï(1) and Ï(2) substituents in 1,4-relation (Schemeâ
1) were synthetized starting with dimethyl 1-methylheptalene-4,5-dicarboxylates 5b and 6b derived from 7-isopropyl-1,4-dimethylazulene (=guaiazulene) and 1,4,6,8-tetramethylazulene by thermal reaction with dimethyl acetylenedicarboxylate. The further general way of proceeding for the introduction of the Ï(1) and Ï(2) substituents is displayed in Schemeâ
3, and the thus obtained methyl heptalene-5-carboxylates of type A and B are listed in Tableâ
1. The C[DOUBLE BOND]C bonds of the 2-arylethenyl and 4-arylbuta-1,3-dien-1-yl groups of Ï(1) and Ï(2) were in all cases (E)-configured and showed s-trans conformation at the C[BOND]C bonds (X-ray and 1H-NOE evidence) in the B-type as well as in the A-type heptalenes (cf. Figs.â
5â12).
All B-type heptalenes showed a strongly enhanced heptalene band I in the wavelength region 440â490â
nm in hexane/CH2Cl2 9â:â1 (cf. Tableâ
4 and Figs.â
13â20). The A-type heptalenes showed in this region only weak absorption, recognizable as shoulders or simply tailing of the dominating heptalene bands II/III (Tableâ
5). Absorption band I of the B-type heptalenes appeared almost at the same wavelength as the longest wavelength absorption band of comparable open-chain α,Ï-diarylpolyenes (cf. Fig.â
21). The cyclic double bond shift (DBS) of the A- and B-type heptalenes could be photochemically steered in one or the other direction by selective irradiation (cf. Fig.â
22)
From blue Azulenes to blue Heptalenes - new strongly polarized Ï-convertible heptalenes
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 (Schemesâ
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; Schemeâ
9), whereas the stronger aminoethenylation agent N,N,NâČ,NâČ,Nâł,Nâł-hexamethylmethanetriamine (=tris(dimethylamino)methane=TDMAM) gave an almost 1â:â1 mixture of 18a and 1-[(1E)-2-(dimethylamino)ethenyl]-5,6,8,10-tetramethylheptalene-4-carboxaldehyde (20b; Schemeâ
11). Carboxylate 15b delivered with DMFDMA on heating in DMF the expected aminoethenylation product 19b (Schemeâ
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 (Schemesâ
13 and 14). The photochemically induced DBS process of the heptalenecarboxaldehydes as âsoftâ merocyanines and their malononitrile derivatives as âstrongâ merocyanines of almost zwitterionic nature were studied in detail (Figs.â
10â29) with the result that 1,4-donor/acceptor substituted heptalenes are cleaner switchable than 1,2-donor/acceptor-substituted heptalenes