Selenodiazole

Semicarbazones of aliphatic and aromatic aldehydes and ketones are converted to 1,2,3-selenodiazoles 41 on oxidation with Se02 , and on pyrolysis these afford alkynes in predominantly high yields (equation 119) . R and R can be H, alkyl and... 

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). 

CHjCSe The preparation of gas phase selenoketene was first reported by a group of microwave spectroscopists in 1978. Pyrolysis of 1,2,3-selenodiazole gave a species whose microwave spectrum in the 18 to 40 GHz region, including transitions of the Se and Se species in natural abundance, was consistent with that expected for CHjCSe. Further observations of deuterium substituted species confirmed the identification and established the structure of the molecule. Selenoketene is a transient species, like thioketene, which dimerizes and polymerizes rapidly at room temperature. Few other seienoketenes have been prepared. 

The reaction mechanism has not been elucidated. Reducing substances presumably release red elementary selenium [1]. Aromatic o-diamines yield highly fluorescent selenodiazoles with selenium dioxide. 

Thiadiazole and selenodiazole rings are isoelectronic with benzene and form a fully conjugated, essentially planar structure when fused to porphyrazines at the p-pyrrolic position (168). Compared to pc, the incorporation of sulfur and selenium in addition to nitrogen atoms to the peripheral heterocyclic rings affects the electronic charge density and influences the interactions between adjacent molecular stacks. 

The peripheral selenodiazole rings of porphyrazine (169) can be opened upon treatment with H2S with the proposed formation of the octaaminoporphyrazine (184), which was not isolated and instead converted into the tetrakis(pyrazino)porphyrazine (185) (Scheme 34) (171). Other heterocycles have been fused on the periphery of porphyrazines, such as l,3-dithiol-2-thione in order to extend the aromatic core (172). Macrocyclization of 4,5-dicyano-l,3-dithiole-2-thione (186) under Linstead conditions in the presence of magnesium butoxide produced the symmetrically substituted tetrakis(l,3-dithiol-2-thiono)porphyrazine (187) (Scheme 35). Due to the low solubility of porphyrazine 181, a consequence of the planar aromatic molecular structure, a full characterization of this compound could not be accomplished. 

The optical spectra of the selenodiazole appended porphyrazines 169, 171, and 172 show maxima of Q bands that are closer to those obtained from phthalocyanines, whereas they differ by 30-40 nm from those of thiadiazole derivatives (174). No splitting of the Q bands was observed for the... 

Electronic Spectra of Thiadiazole and Selenodiazole Porphyrazine Complexes 2... 

Selenodiazoles are prepared by the interaction of sz/m.-diacetyl- or dibenzoyl-hydrazines and phosphorus pentaselenide, or by treating arylselenamides with iodine in alcohol solution. The formulas proposed for these compounds are... 

Table 1 Geometries, rotational constants, and dipole moments of 1,2,5- and 1,3,4-selenodiazoles 3 and 4a...

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. 

Reduction of selenodiazole rings of porphyrazine 203 with H2S in pyridine gave octaamino compound 204, which was converted into other porphyrazine macrocycles, such as compound 205 (Equation 17) <1999MI371>. This method was also applied to porphyrazine containing monoselenodiazole 90 (Equation 18) <2003AGE462, 2003JOC1665>. 

Cocyclization of 3,4-dicyano-l,2,5-selenodiazole 81 and alkene 234 by reaction with Mg(OBu)2 in BuOH, and subsequent demetalation by trifluoroacetic acid and metalation with MnCl2, led to a porphyrazine containing one 1,2,5-selenodiazole ring Mn complex 235 in 59% yield (Equation 29) <2003AGE462, 2003JOC1665>. 

The reaction of 3,4-dicyano-l,2,5-selenodiazole 81 and alkene 236 with Li or MglO-zr-CsHuL in boiling -penta-nol and subsequent demetalation by either acetic acid (Li) or trifluoroacetic acid (Mg) gave unsymmetrical porphyr-azine with 1,2,5-selenodiazole 89 (Equation 30) <2001MC45>. The structure of product 89 was elucidated by single crystal X-ray diffraction. 

These compounds and the corresponding selenodiazoles are reduced [352, 353] like the furazanes in a six-electron reduction o-phenylenediamine and hydrogen sulfide and hydrogen selenide, respectively, are formed. 

Many reactions of substituted diazepines and their fused derivatives frequently relate to a study of the functionality rather than being dependent on the presence of the azepine ring system, most particularly with reduced derivatives. Reaction of the unsymmetrical semicarbazones (110) <91JOC5203> gives the two selenodiazoles (111) and (112), the ratios of which show a solvent dependency (Equation (8)). 

Novel families of phthalocyanine-like macrocycles - porphyrazines with annotated electron-withdrawing 1,2,5-thia/selenodiazole rings 06CCR(250)1530. 

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