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Benzobisthiazole polymers containing mono‐, bi‐, and terthiophene moieties were synthesized through polycondensation in polyphosphoric acid of 2,5‐diamino‐1,4‐benzenedithiol dihydrochloride with thiophene‐2,5‐dicarboxylic acid, 2,2′‐bithiophene‐5,5′‐dicarboxylic acid, and 2,2′:5′,2″‐terthlophene‐5,5″‐dicarboxylic acid, or their corresponding diacid chlorides, respectively. Intrinsic viscosities of up to 8.1 dL/g (methanesulfonic acid, 30°C) were recorded. Polymer structures were verified by elemental analysis and spectroscopic comparison of the polymers with appropriate model compounds. Onset of breakdown under thermogravimetric analysis in air occurred in the 460–590°C range with the benzobisthiazole polymers containing a monothiophene linkage being the most stable. Films suitable for third‐order optical susceptibility measurements could be prepared by extrusion techniques from the benzobisthiazole polymer containing a monothiophene linkage. Degenerate four wave mixing measurements on this film yielded a third order optical susceptibility χ(3) of approximately 4.5 × 10−10 esu. © 1993 John Wiley & Sons, Inc.

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A series of 5‐alkoxy‐ and 5‐acetoxy‐4,4‐dimethyl‐3,3,5‐trisubstituted‐4,5‐dihydro‐3H‐pyrazoles 2a‐f (hexasubstituted pyrazolines) was synthesized by oxidation of the corresponding 3,4‐dihydro‐2H‐pyrazoles with lead tetraacetate in the appropriate solvents. The 5‐acetoxy compounds were produced when the oxidations were carried out in methylene chloride. Oxidation with lead tetraacetate in dry alcoholic solvents resulted in the formation of the 5‐alkoxy derivatives as the major products. Thermolysis of the hexasubstituted‐4,5‐dihydro‐3H‐pyrazoles 2a‐f in cyclohexane or as the melt at high temperature yielded the 1‐alkoxy‐ and 1‐acetoxy‐1,2,2,3,3‐pentasubstituted cyclopropanes 3a‐f in good yields. Trace amounts of alkene products were formed in several reactions. No products attributable to cycloreversion pathways were detected. The product distributions were consistent with extrusion of nitrogen gas from 2a‐f to yield the singlet 1,3‐diradical, closure of which resulted in cyclopropane formation with partial retention of stereochemistry.