Nonclassical Heterocycles. 6. Tri- and Tetracyclic Ring Systems Containing a "Nonclassical" Thiophene Nucleus

Article abstract of DOI:10.1021/jo01289a019

The in situ generation of azomethine imine ylides from 1-aminopyridinium, 1-aminoquinolinium, and 2-aminoisoquinolinium salts and their subsequent cycloaddition to dibenzoylacetylene has been utilized as a route to a series of 2,3-dibenzoylpyrazolo<1,5-a>pyridines, to 2,3-dibenzoylpyrazolo<1,5-a>quinoline and to 1,2-dibenzoylpyrazolo<5,1-a>isoquinoline, respectively.Treatment of these dibenzoyl heterocycles with P4S10/pyridine readily gave several new "nonclassical" thiophene ring system, the thieno<3,4-b>pyrazolo<1,5-a>pyridine-2-S^IV system containing 14? electrons and the thieno<3',4':3,4>pyrazolo<1,5-a>quinoline-2-S^IV and the thieno<3',4':3,4><5,1-a>isoquinoline-2-S-^IV systems each containing 18? electrons.The diketones also reacted readily with hydrazine forming the corresponding ring-fused pyridazines.Cycloaddition with fumaronitrile and N-phenylmaleimide occurred exclusively across the thiocarbonyl ylide dipole of these "nonclassical" thiophene ring systems, H2S being eliminated from the initial 1:1 cycloadducts under the thermal reaction conditions.However, dimethyl acetylenedicarboxylate and dibenzoylacetylene only underwent cycloaddition with those ring systems containing the quinoline and isoquinoline systems, sulfur being extruded readily from the initial 1:1 cycloadduct. 8,9-Dibenzoyl-7,10-diphenylbenzopyrazolo<1,5-a>quinoline prepared in this way was also converted with P4S10/pyridine into the thieno<3',4':8,9>benzopyrazolo<1,5-a>quinoline-9-S^IV ring system, a stable tetravalent sulfur system containing 22? electrons in which cycloaddition also occurred across the thiocarbonyl ylide dipole.With dimethyl acetylenedicarboxylate, sulfur was extruded from the initial 1:1 cycloadduct, whereas with fumaronitrile, the initial 1:1 cycloadduct itself was isolated.Incoporation of a tetravalent sulfur atom into a heterocyclic system and cycloaddition with olefinic or acetylenic dipolarophiles provide a convenient means of annulation of a benzene ring containing a variety of functional groups to the heterocycli system.