1.2- Diselenol-3-ones

One of the rare examples in which selenium is involved as a donor atom results from the reaction of Tc-gluconate with 2 equivalents of l,l-dicyanoethene-2,2-diselenolate (dcds), which gives the selenium analogue of (87), [TcO(dcds)2], in 50% yield. The complex was structurally characterized and shown to be square pyramidal, with Tc— Se averaging 2.474 A and the Tc 0.88 A above the basal plane. ... 

The tendency of intermediate heterocyclic ditellurides to eliminate one of the tellurium atoms thus contracting the size of the ring is illustrated by the course of the oxidative cyclization of the dilithio dichalcogenides 78 (84JHC413). Whereas in the case of the diselenolate 78 (M = Se) the expected heterocyclic diselenide 79a is formed, albeit in low yield, the analogous reaction with the ditellurolate 78 (M = Te) results in an extrusion of elemental tellurium affording dibenzotellurophene 79b. 

Reviews have appeared on benzo-l,3-dithioles, -diselenoles and -ditelluroles [93SR103], the organic chemistry of l,3-dithiol-2-one-4,5-dithiolate ("DMIT") [95S215], and various... 

A related reaction involves directly treating a mixture of the tetrahydroselenopyran-4-one 101 with a dithiathione or dithiaselone 102 with triethylphosphite in refluxing benzene (Equation 44) <1993J(P2)1815>. A variety of selenotetrahydropyranylidene-l,3-dithioles and diselenoles 103 has been prepared using this method. 

Dimethyl-y-pyrone reacts with sodium selenide (or sodium hydrogen selenide) to give 2,6-dimethyl-4-seleno-y-pyrone (66). This, in turn, reacts with sodium selenide to give 4,6-bis(hydroseleno)-3,5-heptadien-2-one (67), which is readily oxidized by air to 5-methyl-l,2-diselenol-3-yIidene acetone (68).84,85... 

Very few structural investigations have been made for five-membered heterocycles containing selenium or tellurium and one other chalcogen atom by either theoretical methods or X-ray diffraction. The lone theoretical treatment <8lJST(7l)l) was a MINDO/3 optimization of molecular geometry for l,3-thiaselenole-2-thione and -2-selenone and for 1,3-diselenole-2-selenone (8) and -2-thione. These molecules were predicted to be planar. The calculated bond lengths and angles for (8) are shown in Scheme 3. 

The photochemical couplings of 4,5-diphenyl- and 4-phenyl-l,3-diselenole-2-thione to give tetraphenyl- and diphenyl-tetraselenafulvalene, respectively, and elemental sulfur have been reported (79ZC192). In this same report the irradiation of 4,5-diphenyl-l,3-thiaselenol-2-one (52) in the presence of nickel tetracarbonyl gave the nickel thiaselenane (53). 

The redox properties of donor-rt-acceptor molecules 24 and 40-44 are collected in Table 5 <1998T13257>. The compounds display a reversible one-electron oxidation wave, which corresponds to the formation of the radical cation of the 1,3-diselenole donor moiety, and an irreversible one-electron reduction wave forming the radical anion located on the dicyanomethylene or A -cyanoimine group. The derivatives 24 and 44 are both easier to oxidize and reduce than the other compounds, which is explained by the gain of aromaticity of the spacer unit. The second one-electron reduction of these compounds is ascribed to reduction of the anthracene unit. 

The 1,2,3-selenadiazole route to l,3-diselenole-2-chalcogenones (i.e., l,3-thiaselenole-2-thione <1980JOC2632>) was described in detail in CHEC-11(1996). Here one more recent example is shown. 1,2,3-Selenadiazole 254 was treated with isoselenocyanatobenzene and potassium tert-hutoxide in A)A -dimethylformamide and /7-butanol to provide 2-phenylimino-l,3-diselenole 25 in 50% yield (Equation 61) <1996RJC1641, 1996RJ01812>. Compounds 37, 38, and 255 were made in a similar way by cycloaddition reactions <1996RJ01812>. 

The efficient one-pot syntheses of l,3-diselenole-2-selones described in Equations (53)-(57) also deserve special attention. Overall, the chemistry of fulvenes and fulvalenes evidently dominate this chapter. 

Treatment of 2,3-diphenylcyclopropenone with sodium hydrogen selenide in ethanol under a nitrogen atmosphere produced 4,5-diphenyl-3//-l,2-diselenol-3-one in 45% yield. 

Of the two reports of selenium co-ordination complexes, one involves nickel(ii) and copper(ii) complexes of piperidine-, morpholine-, and thiomorpholinediseleno-carbamates (84). The quadridentate selenoether l,3-bis(methylselenoethylseleno) propane (bsep) has been synthesized from the newly prepared propan-l,3-diselenol,... 

The l,2-diselenol-3-one (46) is easily protonated in trifluoroacetic acid, which results in a shift of the protons to lower field in the H NMR spectrum <87KGS855>. 

Diphenyl-l,2-diselenol-3-one and thiophosgene reacted with the formation of 3-chloro-4,5-diphenyl-1,2-diselenolylium chloride which was further reduced by Zn to 3,3 -bis(4,5-diphenyl-l,2-diselenol-ylidene), (1,2-TSeF) according to Scheme 5 <88BSF101>, 1,2-TSeF is one of the few known TSeFs <93SR245>. 

Thermal and electron-induced fragmentation of l,3-diselenole-2-ones are parallel as loss of CO is observed in both cases. Vacuum pyrolyses of either l,3-diselenole-2-one or l,3-thiaselenole-2-one (22) give rise to formation of CO and 1,2-diselenete or 1,2-thiaselenete (23), respectively (Equation (1)) <87AG348>. 

One of the most versatile preparations of the 1,3-diselenole ring system is the 1,3-cycloaddition. An overview of the cycloaddition route of 1,3-diselenoles either from a 1,2,3-selenadiazole or by the acetylide route is given in Scheme 49. 

Since 1,2-diselenides on reduction with NaBH4 give diselenolates, 1,3-diselenolane acts as a small ring suitable for conversion to a larger one as shown in Scheme 15 <89CC1789>. 

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