BENZENESELENENYL CHLORIDE

Benzeneselenenyl chloride (benzeneselenyl chloride, phenylselenenyl chloride) [5707-04-0] M 191.5, m 59-60 , 64-65 , b 92 /5mm, 120 /20mm. Purified by distn in vac and recrystn (orange needles) from hexane [Foster J Am Chem Soc 55 822 1933, Foster et al. Reel Trav Chim, Pays-Bas 53 405, 408 1934-, Behaghel and Seibert Chem Ber661 4 1933.] HIGHLY TOXIC. 

Ketones react slowly wilh benzeneselenenyl chloride in the presence of HCl to yield a-phenylseleno ketones. Propose a mechanism for this acid-catalyzed tt-subslitution reaction. 

Diphenyl diselenide has been prepared by disproportionation of phenyl selenocyanate in the presence of potassium hydroxide" or ammonia/ and by air oxidation of benzeneselenol. The preparation of benzeneselenol is described in an earlier volume in this series/ In the present procedure phenylselenomagnesium bromide formed from phenylmagnesium bromide and selenium is oxidized directly to diphenyl diselenide with bromine/ Thus the liberation of the malodorous and toxic hydrogen selenide and benzeneselenol is avoided. Benzeneselenenyl chloride has been prepared by thermal elimination of ethyl chloride from ethyl phenyl selenide di-chloride/ by thermal elimination of chlorine from phenylselenium trichloride," and by chlorinolysis of diphenyl diselenide with either sulfuryl chloride " or chlorine. " ... 

Benzenediamine, 57, 34 Benzeneselenenyl acetate, 59, 144 Benzeneselenenyl bromide, 59, 60, 144 BENZENESELENENYL CHLORIDE,... 

REAGENTS FOR SYNTHESIS OF ORGANOSELENIUM COMPOUNDS DIPHENYL DISELENIDE AND BENZENESELENENYL CHLORIDE... 

Organosei nium Reagents Prepared from Diphenyl Diselenide or Benzeneselenenyl Chloride... 

The same reaction scheme can also explain the stereochemical behavior of the addition of benzeneselenenyl chloride to 108 in methanol, which gives, in addition to the trans adduct 138, the analogous methoxy derivative 146, the cross-bonded chlorides 147 and 148, and the analogous epimeric methoxy adducts 149 and 150 (equation 130). 

The involvement of at least three different forms of the seleniranium ion intermediate, i.e. tight and solvent-separated ion pairs and free ions, has been invoked also to rationalize the different chemical behavior observed in the addition of benzeneselenenyl chloride to bicyclo[2.2.1]hepta-2,5-diene (49) in methanol and in methylene chloride140. As stressed by the authors, the addition of benzeneselenenyl chloride to 49 shows a number of interesting trends. Four products (151-154), all resulting from homoallylic attack, were isolated from the reaction carried out in methanol (equation 131). Furthermore, it... 

A solvent-dependent chemoselectivity, pointing to a dependence of the relative reactivities of the 1,2- and 1,1-disubstituted double bonds on solvent polarity and nucleophilicity, has been observed in the reaction of benzeneselenenyl chloride with 2-methylenebicyclo[2.2.1]hept-5-ene (159) which gives products 160-163140. In methylene chloride the reaction occurs with a moderate chemoselectivity, attack on the endocyclic bond being preferred over that on the exocyclic one in a 60 40 ratio. In methanol, the addition is completely chemoselective and the attack occurs exclusively on the endocyclic double bond (equation 132). It may be further noted that 162 and 163 isomerize and solvolyze at high temperatures, leading to the homoallylic products 160 and 161. 

The transformation of 163 into 160 and 161 has been interpreted in terms of a reversible addition sequence, in which 159 and benzeneselenenyl chloride are regenerated and then react to give the more stable adducts 160 and 161. 

On treatment with benzeneselenenyl chloride two olefinic urethanes (214 and 217) underwent cyclization to afford piperidine derivatives (215 and 218, respectively) having the cis stereochemistry. Their reduction with triphenyltin hydride gave the same product (216). Removal of the blocking group from the nitrogen gave ( )-isosolenopsin A (Ic) (Scheme 6) (392). 

Pyrrolidines piperidines.7 Reaction with benzeneselenenyl chloride converts A4-and As-unsaturatcd ethyl urethanes into phcnylseleno-substituted pyrrolidines and piperidines, respectively. Yields are considerably improved by the presence of silica gel, which presumably facilitates the ring closure subsequent to addition of the reagent to the double bond (equation I). 

Methylthiomethyl p-tolyl sulfone, 192 Potassium ruthenate, 259 Trimethylsilyl chlorochromate, 327 a-Substituted ketones (see also Halo carbonyl compounds, Hydroxy aldehydes and ketones) a-Acetoxy ketones Benzeneselenenyl chloride-Silver acetate, 27... 

The final step in a recent synthesis of cannabichromene (2) is the aromatization of the cyclohexenone ring of 1. Reagents used for this purpose also attack the double bond in the side chain, but the desired reaction was effected by treatment of the lithium enolate of 1 with benzeneselenenyl chloride followed by selenoxide elimination in the presence of 3,5-dimethoxyaniline.5... 

Cyclization of unsaturated benzyl carbamates. Iodine induces cyclization of unsaturated benzyl carbamates. Benzeneselenenyl chloride is less effective for this reaction.14 Examples ... 

Benzeneselenenyl bromide-silver nitrite, 33 Benzeneselenenyl chloride-aluminum chloride. 33-34... 

Ally lie alcohols from allylsilanes. The adducts of benzeneselenenyl chloride to ullylsilanes on treatment with SnCl2 or Florisil undergo dechlorosilylation and rearrangement to give the less substituted allyl selenide. When oxidized, the allyl selenidcs are converted into the allylic alcohol in which the hydroxyl group occupies (lie more substituted site (6, 338). 

Dihydro-2//-pyrido[l,2-a]pyrimidin-2-one 675, a neutral hydrogen chloride acceptor, has been shown to give better yields in regio- and stereospecific thio- and selenolactonizations of hept-4-ynoic and hex-4-ynoic acids 683 with benzenesulfenyl and benzeneselenenyl chlorides than triethylamine [86JCS(P1)1999]. In the case of dihydropyrido[l,2-a] pyrimidinone 675, noncyclized products 685 and 686 were formed only in trace amounts. 

Oxidative contraction of glycols.1 Reaction of 3,4-dihydro-2//-pyran (1) with benzeneselenenyl chloride and then with methanol provides the adduct 2, which is oxidized by m-chloroperbenzoic acid to the ring-contracted aldehyde 3 (cf., 12, 120). Application of this sequence to the tribenzyl-D-glucal (4) furnishes the adduct... 

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