Addition of selenols

There are several reviews that enumerate the many methods that effect the addition of H—SeR to C—C multiple bonds.558,559 Of these, only a few methods involve true electrophilic additions of selenols to C—C multiple bonds. High yields of the Markovnikov product are reported when the relatively acidic... 

Radical Addition of Selenols and Diselenides to Alkynes and Allenes... 

Pd(OAc)2-catalyzed hydroselenation of alkynes with PhSeH can be applied to the hydroselenation of allenes (Scheme 15.83). Whereas radical addition of selenols to allenes leads to fhe formation of regioisomeric mixtures of vinylic selenides [145], the Pd(OAc)2-catalyzed hydroselenation provides the corresponding vinylic selenides with moderate to high regioselectivity [163]. 

Scheme 23 Reaction pathway of addition of selenol ester to alkyne...

Addition of selenols to unsatd. carbon-carbon bonds s. 18, 704... 

Benzeneselenol as a representative selenol is a colorless liquid of greater acidity than benzenethiol (p a = 5.9 (PhSeH) 6.5 (PhSH)). The bond energy of Se-H is 73 kcal/mol, is smaller than S-H (87 kcal/mol) [82]. These properties may contribute to the efficiency in the oxidative addition of selenols to low-valent transition metals, ligand-exchange reaction between high-valent transition metal complexes and selenols, and protonation process of carbon-metal bonds. Indeed, several transition metal complexes catalyze the highly selective hydrothiolation of alkynes and allenes. 

Nickel-selenium coordination compounds have received attention in recent years, because a unique Ni-selenocysteine interaction was revealed in the active site of [FeNiSe]-hydrogenases.1083,1084 Of particular interest in this regard are mixed CO/selenolate complexes. Distorted square planar (393) was prepared from [CpNi(CO)]2, PhSeSePh, and [Fe(CO)3(SePh)3] and provides the first example of CO bound to a square planar Ni11 center in thiolate/selenolate environment.1085,1086 Upon addition of RSSR, species of the series [Ni(CO)(SR) (SePh)3 ] are formed. //(CO) ranges from 2,023 cm-1 to 2,043 cm-1 and is regarded as a spectroscopic reference for the CO binding site in [NiFeSe] hydrogenases. 

Ono and Kamimura have found a very simple method for the stereo-control of the Michael addition of thiols, selenols, or alcohols. The Michael addition of thiolate anions to nitroalkenes followed by protonation at -78 °C gives anti-(J-nitro sulfides (Eq. 4.8).11 This procedure can be extended to the preparation of a/jti-(3-nitro selenides (Eq. 4.9)12 and a/jti-(3-nitro ethers (Eq. 4.10).13 The addition products of benzyl alcohol are converted into P-amino alcohols with the retention of the configuration, which is a useful method for anri-P-amino alcohols. This is an alternative method of stereoselective nitro-aldol reactions (Section 3.3). The anti selectivity of these reactions is explained on the basis of stereoselective protonation to nitronate anion intermediates. The high stereoselectivity requires heteroatom substituents on the P-position of the nitro group. The computational calculation exhibits that the heteroatom covers one site of the plane of the nitronate anion.14... 

The lO-E-4 chalcogen(IV) species diphenylselenium(IV) dibromide (1, Fig. 1) and diphenyltellurium(IV) dibromide (2, Fig. 1) oxidize thiophenol to diphenyl disulfide in nearly quantitative yield as shown in equations (13) and (14). Tellurium(IV) dihalides 6-11 also oxidize thiophenol to diphenyl disulfide and benzene selenol to diphenyl diselenide. Similarly, the 12-Te-5 molecule dioxatellurapentalene 45 (Fig. 19) is a mild oxidant for ethylmercaptan, thiophenol, and benzene selenol giving diethyl disulfide, diphenyl disulfide, and diphenyl diselenide in essentially quantitative yield. As shown in equation (15), 1,1,5,5,9,9-hexachloro-1,5,9-tritelluracyclododecane oxidizes six molecules of thiophenol to diphenyl disulfide and 1,5,9-tritelluracyclododecane in 90% yield. In contrast, 12-Te-5 pertellurane 44 and 12-Se-5 perselenane 46 do not oxidize thiophenol to diphenyl disulfide. Instead, these molecules undergo a nucleophilic addition of thiophenol followed by cleavage of the tellurium-carbon or selenium-carbon bond. ... 

Nucleophilic additions of alcohols, amines, thiols, and selenols to Group 8 buta-trienylidene intermediates [M]=C=C=C=CR2 have also been used in the preparation of stable heteroatom-conjugated allenylidene complexes. Thus, activation of trimethylsilyl-l,3-butadiyne HC=C-C=CSiMe3 by the iron(II) complex [FeClCp (dppe)], in methanol and in the presence of NaBPh4, resulted in the high-yield formation of the methoxy-allenylidene [FeCp =C=C=C(OMe)Me ... 

The syntheses of 2-ketobenzo[ >]selenophene (134) (76JCS(P1)2452) and its benzo[c] counterpart (135) (64BSB491, 81JHC343) both depend on intramolecular acylation of an intermediary selenol, while in the benzo[Z>]selenophene (137) preparation from (136) the ring closure depends upon the intramolecular addition of the intermediary selenol to the carbonyl group (70BSB235). 

The oxidative addition of chalcogen-chalcogen bonds in RE—ER is widely applied in transition metal chemistry and is often a useful route for the preparation of thiolates, selenolates and, to a more limited extent, tellurolates. The oxidative addition of X2 = HO—OH and PhC(0)0—0C(0)Ph is also known and, in the case of Ptu complexes, gives predominantly trans products 47... 

Se/eno/eslers, R SeCfiHs. Oxidation of N-acylhydrazines with benzeneseleninic acid in CH2CI2 leads to selenol esters, presumably via a diazene. Yields are usually increased by addition of triphenylphosphine and are then in the range... 

Addition of the selenolate that is prepared from diphenyl diselenide by reduction with NaBH4 to conjugate enyne sulfones 20 occurs at the d-position of the sulfonyl group to give 4-phenylseleno-l-sulfonylbuta-1,3-dienes 21 regio- and stereoselectively (Scheme 28) [50]. On the other hand, addition of PhSeNa to the conjugated alkynyl sulfone 22 that has a -phenylseleno substituent affords the anti-Michael adduct 23 preferentially (Scheme 29) [51]. 

The addition of alcohols to N-alkylidene selenoamides generated in situ leads to N-alkoxyalkyl selenoamides [84]. The substitution reaction of alkoxy groups of selenoesters [RC(Se)OR ] with aluminum thiolates or selenolates proceeds smoothly to give the corresponding esters [RC(Se)SR, RC(Se)SeR ] [7a, 85], whereas the addition of thiols to selenoaldehydes takes place at the selenium atom to afford selenenesulfides (RCH2SeSR ) [86]. 

The indium selenolate [PPh4][In(SePh)4] can be prepared by treating InCla with NaSePh, followed by the addition of [PPh4]Cl. Interestingly, if the product resulting from InCl3 and... 

In 1962 Renson et al. reported that a variety of selenol esters can be synthesized by the reaction of the appropriate acyl chlorides with selenols in the presence of pyridine. - Selenols can easily be prepared from elemental selenium and the corresponding Grignard reagents. In addition to simple selenol esters, a,P-unsaturated selenol esters (4) and (5) and o-substituted aromatic selenol esters (6) have been obtained by this method, as shown in Scheme 1. Butyl selenol esters are generally colorless or light yellow liquids, whereas the phenyl or substituted phenyl selenol esters are white solids, which are easily purified by recrystallization. More recently other groups have used Renson s method to synthesize similar selenol esters. " ... 

Reaction of carboxylic acids with phenyl dichlorophosphate, followed by the addition of bensenesele-nol to the mixture afforded selenol esters (Scheme 4). The reaction is assumed to proceed via the penta-covalent oxyphosphorane intermediates (11a) and (11b). 

Another approach to the synthesis of the parent compounds involves 35) the reaction of 1-ethoxy-1-trimethylsilyloxy cyclopropane prepared according to the Ruhlman method 112) and selenols, in the presence of zinc chloride (Scheme 31 a). The reaction is quite rapid with methylselenol35) but much more difficult with phenylselenol3> 35). It takes a completely different course when an alkyl substituent is present on the cyclopropane ring114). Surprisingly thus methylselenol cleaves n4> the cyclopropane ring of 1-ethoxy-l-trimethylsilyloxy-2-ethyl cyclopropane 11S) on addition of zinc chloride and lead114> to 1,1 -bis(methylseleno)pentane by reductive selenoacetalisation (Scheme 31b). 

Addition reactions. CAN serves as a catalyst for the conjugate addition of thiols and selenols to enones under solvent-free conditions. Glycals are transformed into glycosides containing a nitromethyl group at C-2. ... 

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