Selenodiazole synthesis

As an extension of work on synthesis of strained cycloalkynes, trans- and tw-cyclopropane-fused medium ring (9-11-membered) cycloalkynes 108-111 and 113 were synthesized by thermolysis of 1,2,3-selenadiazoles 63, 105-107, and 112 with copper powder at 190-240 °C (Scheme 3) <1997LA1557>. /ra j-Bicyclo[7.1.0]dec-2-yne 108 is highly strained and has a low kinetic stability toward polymerization. Only traces of compound 108 were detected in the thermolysis of selenodiazole 63. The trapping with tetraphenylcyclopentadienone yielded an adduct 114 in 20% yield, whereas precursor 105 gave product 115 in 44% yield. 

The Hurd-Mori cyclization and Lalezari cyclization of a-methylene ketones are by far the most widely used routes to 1,2,3-thiadiazole and 1,2,3-selenodiazole, respectively.This approach has been applied in the synthesis of a variety of 1,2,3-thiadiazoles 129 (13JHC630) andl31 (13OT4038) from the corresponding hydrazones. Thiadiazoles 132, derived from 131, can be effectively converted to benzothiophene derivatives (see Section 5.5.4.2). 

Application of the Lalezari reaction is highlighted in the synthesis of 1,2,3-selenodiazoles 134, which serve as the precursors of a series of novel 2-aminobenzo[ ]selenophenes (see Section 5.5.4.2) (130L1744). 

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