Sequential approach to the synthesis of ‘U and Z’ shaped polycyclic heteroarenes

Abstract

The synthesis of three new classes of heteroarenes, built through the sequential fusion of naphthalene, benzo/naphtho[b]oxepine and thiochromene rings with pyran and pyrimidine ring systems to give 'U and Z' shaped structural frameworks is reported. The methodology is based on the synthesis of pyran fused intermediates, 1-methylthio-3-oxo-5,6-dihydro-3H-benzo[f]chromene-2-carbonitrile (3), 4-methylthio-2-oxo-5,6-dihydro-2H-benzo/naphtho[b]pyrano[2,3-d]oxepine-3-carbonitriles (10, 20) and 4-methylthio-2-oxo-2,5-dihydrothiochromeno[4,3-b]pyran-3-carbonitriles (15) from the reaction of 2-tetralone, benzo/naphtho[b]oxepin-5-ones and thiochromen-4-ones with methyl 2-cyano-3,3-dimethylthioacrylate respectively. Further condensation of intermediates 3, 10, 20 and 15 with amidines led to the formation of tetracyclic 'U' shaped 4-amino-2-aryl-7,8-dihydro-5-oxo-5H-naphtho[2,1-b]pyrimido[4,5-d]pyrans (8) and 'Z' shaped 4-amino-2-aryl-5-oxo-12,13-dihydro-5H-benzo/naphtho[b]oxepino[5,4-b]pyrimido[4,5-d]pyrans (12, 22) and 4-amino-2-aryl-5-oxo-5,12-dihydrothiochromeno[4,3-b]pyrimido[4,5-d]pyrans (17). Compound 12f forms a chain of dimers through N-HO interactions as indicated by the X-ray structure analysis, and the quantum chemical calculations performed at the MP2 level indicate that this interaction energy is 10 kJ mol(-1).

Natural and Synthetic Chromenes, Fused Chromenes, and Versatility of Dihydrobenzo[h]chromenes in Organic Synthesis

“…Besides broad medicinal applications of quinolines as antimalarials, antibacterial, and anti-inflammatory , agents, they are also useful as agrochemicals . This class of compounds is prepared simply through ring transformation of benzo­[ h ]­chromenes by amidines or isothiourea .…”

“…Under analogous conditions, the ring transformation of benzo­[ f ]­chromene 493 , obtained from the reaction of 2-tetralone with methyl 2-cyano-3,3-dimethylthioacrylate using powdered KOH as a base in DMF and was used as precursor for the ring transformation reactions. Thus, stirring a mixture of 493 with ammonium carbonate in boiling pyridine afforded benzo­[ f ]­quinolines 494 , Scheme .…”

“…Ring-opening reaction has been observed and reported when 2-oxobenzo­[ f ]­chromene-3-carbonitrile 493 was refluxed in ethanol with 2 equiv of sec -amine to yield two ring-opened compounds 503 and 504 , Scheme . The structure of the isolated compounds was confirmed in the spectroscopic studies.…”

Strategy to Construct Stair‐Shaped Partially Reduced Naphtho[1,2‐b]pyrano[2,3‐d]oxepines and Dinaphtho[1,2‐b,d]oxepines

“…Although the chemistry of 2‐pyranone is well developed and plenty of literature is available , the synthesis and ring transformation studies of partially reduced suitably functionalized benzo[ b ]oxepine ( III ) and naphtho[ b ]oxepine ( IV ) (Fig. ) fused 2‐pyranone system are meagerly developed. However, extensive literature survey revealed that the chemistry of 2‐oxo‐5,6‐dihydro‐2 H ‐naphtho[1,2‐ b ]pyrano[2,3‐ d ]oxepine‐5‐carbonitrile ( IV ) is not developed so far.…”