[Dimers from o-nitrobenzylidene acetoacetic esters].

The o-nitrobenzylidene acetoacetic esters 1 dimerize in the presence of BuLi or LDA to give the cyclohexenes 2 in poor yield. Two diastereomer of 2b were isolated, whose configuration is deduced by nmr-spectroscopic methods.

[Biphenyl derivatives as by-products from the synthesis of 4-aryl-4H-pyrans].

The reaction of the 1,5-diketones 1 with acetic anhydride/acetic acid in the presence of zinc chloride yields the 4-aryl-4H-pyrans 2 as main products. The annulated lactone 3 and the cyclohexene derivatives 5 are isolated as by-products. The configuration of the cyclohexanone 4a and the cyclohexenes 5 are deduced from nmr spectroscopic methods.

[Isomeric phenanthridines from 1,2-dihydro-5-methyl-2'-nitro-[1,1'-biphenyl]-2,6-dicarboxylic acid esters].

Hydrolysis of the dienamine function of the dihydrobiphenyls 3 leads to a mixture of the tautomers 4A-C (NMR). The structures of the starting material 3a and the products 4cA and 4bC are confirmed by X-ray crystal analysis. The biphenyls 5 are formed by dehydrogenation of 3 with iodine, whereas 4b produced the additional iodinated compound 6.

[Pyrano[3,4-c]quinolines from 1-desaza--oxa-nifedipine].

Pyrano[3,4-c]quinolines from 1-desaza-1-oxa-nifedipine The reaction of the 1,5-diketone 1 with acetic anhydride/acetic acid in the presence of zinc chloride yields the 1-desaza-1-oxa-nifedipine 2 and the annulated lactone 3 as a by-product. The structures of 2 and 3 are confirmed by X-ray structure analysis. The pH-dependent reduction of the nitro group from 2 leads to the pyrano[3,4-c]quinolines 4Aa, b by ring closure.

[Bis(lactone)-annulated 4H-pyranes and 1,4-dihydropyridines from 3,3'-(nitrobenzlidene)-bistetronic acids].

The bistetronic derivatives 4, obtained by base catalyzed reaction of the aldehydes 3 with surplus tetronic acid (2), cyclize in polyphosphoric acid (PPA) to yield the 4H-pyranes 5. The amino derivative 6 formed by reduction of the nitro group of 5a easily splits to give the furoquinoline 7 and 2. By heating the ammonium bistetronate 8 ring closure occurs leading to the bisannulated 1,4-dihydropyridine (DHP) 9.

[Synthesis, structure and stability of 4-aryl-4H-pyran-3,5-dicarboxylic acid esters].

Eight new 4-aryl-2,6-dimethyl-4H-pyrane-3,5-dicarboxylic acid esters 2 and a new 2-amino-2-nor derivative 7 are synthesized using known methods, whose limitations are shown. In contrast to the isoelectronic 4-aryl-1,4-dihydro-pyridines (DHP) 1 the compounds 2e, g possess a nearly planar heterocycle, as found by X-ray crystal structure analysis. The 4H-pyrane-3,5-dicarboxylic acid ester 2e with m-substitution exhibits s-cis/s-cis-conformation, while compound 2g with o-substitution of the aromatic ring represents s-cis/s-trans-conformation.