Phenylselenenyl bromide

In an effort to make productive use of the undesired C-13 epimer, 100-/ , a process was developed to convert it into the desired isomer 100. To this end, reaction of the lactone enolate derived from 100-) with phenylselenenyl bromide produces an a-selenated lactone which can subsequently be converted to a,) -unsaturated lactone 148 through oxidative syn elimination (91 % overall yield). Interestingly, when 148 is treated sequentially with lithium bis(trimethylsilyl)amide and methanol, the double bond of the unsaturated lactone is shifted, the lactone ring is cleaved, and ) ,y-unsaturated methyl ester alcohol 149 is formed in 94% yield. In light of the constitution of compound 149, we were hopeful that a hydroxyl-directed hydrogenation52 of the trisubstituted double bond might proceed diastereoselectively in the desired direction In the event, however, hydrogenation of 149 in the presence of [Ir(COD)(py)P(Cy)3](PF6)53 produces an equimolar mixture of C-13 epimers in 80 % yield. Sequential methyl ester saponification and lactonization reactions then furnish a separable 1 1 mixture of lactones 100 and 100-) (72% overall yield from 149). 

Similar compounds were prepared via the same method, from the reaction of the same substrates with phenylsulphenyl- and phenylselenenyl bromides (Scheme 42) [105],... 

The same substrates react with phenylselenenyl bromide to give only 2,5-dihydro-l,2-oxaphosphole-2-oxide derivatives (Scheme 71) [149],... 

Compounds 181 react with alkylsulphenyl chlorides to form a mixture of 1,2-oxaphosphole derivatives and 1,2-adducts in 4 1 ratio. Decreasing the reaction temperature favored formation of oxaphosphole product. The same substrates reacted with phenylsulphenyl- and phenylselenenyl bromides to give only 1,2-oxaphosphole derivatives [133],... 

On reacting the same substrates with phenylsulphenyl- and with phenylselenenyl bromides, relatively stable cyclic phosphonium salts 74 were obtained (Scheme 29) [82],... 

A cysteine residue was incorporated into the protein backbone in a specific position and activated to thioglycosylation by treatment with phenylselenenyl bromide. The electrophilic character of the sulphur atom in the resulting S-Se bond makes possible its nucleophilic substitution by 1-thio mono- or oligosaccharides (Fig. 26).55... 

Crich and Rumthao reported a new synthesis of carbazomycin B using a benzeneselenol-catalyzed, stannane-mediated addition of an aryl radical to the functionalized iodocarbamate 835, followed by cyclization and dehydrogenative aromatization (622). The iodocarbamate 835 required for the key radical reaction was obtained from the nitrophenol 784 (609) (see Scheme 5.85). lodination of 784, followed by acetylation, afforded 3,4-dimethyl-6-iodo-2-methoxy-5-nitrophenyl acetate 834. Reduction of 834 with iron and ferric chloride in acetic acid, followed by reaction with methyl chloroformate, led to the iodocarbamate 835. Reaction of 835 and diphenyl diselenide in refluxing benzene with tributyltin hydride and azobisisobutyronitrile (AIBN) gave the adduct 836 in 40% yield, along with 8% of the recovered substrate and 12% of the deiodinated carbamate 837. Treatment of 836 with phenylselenenyl bromide in dichloromethane afforded the phenylselenenyltetrahydrocarbazole 838. Oxidative... 

It has been observed that 4-pentenyl amides such as 1 cyclize to lactams 2 on reaction with phenylselenenyl bromide. The 3-butenyl compound 3, on the other hand, cyclizes to an imino ether, 4. What is the basis for the different course of these reactions ... 

N-(4-Pentenyl)-acetamide konnen als Ausgangsmaterial zur Synthese von 2-Methyl-pyrrolidinen eingesetzt werden. Hire Kondensation mit Phenylselenenyl-bromid und De-phenylselenylierung des so erhaltenen 2-(Phenylseleno-methyl)-pyrrolidin-Derivates fuhrt zum l-Acetyl-2-methyl-pyrrolidin3, das in bekannter Weise (s.S. U87ff. sowie Bd. XI/1, S. 926) zum freien Amin (d. h. z. B. zu 2-Methyl-pyrrolidin oder 4-Ethyl-2-methyl-pyrrolidin) gespalten werden kann. 

The dehydrogenation of pyrrolidines having exocyclic methylene groups has been accomplished with phenylselenenyl bromide (equation 152) (75JOC800). Recent advances in the methods for construction of the starting materials may permit further expansion of this method (81JOC3671, 71HCA710). 

There are various ways to generate and synthesize selenium electrophiles and some of these compounds are commercially available. The addition reaction can also be dependent on the counterion X of these reagents and several protocols have been developed to exchange the counterions. The most commonly used electrophile is the phenylselenyl electrophile and compounds like phenylselenenyl chloride 6 and phenylselenenyl bromide 7 are commercially available. They can also be easily generated from diphenyl diselenide 8 by treatment with sulfuryl chloride or elementary chlorine or bromine, respectively. Diselenides in general are very versatile precursors for selenium electrophiles. For addition reactions using external nucleophiles the use of selenenyl halides can lead to complications, because chloride or bromide ions can also act as nucleophiles and lead to undesired side-products. An... 

In the presence of base, phenylselenenyl bromide reacts with alkenyldihydroxyboranes to give alkenyl phenyl selenides with retention of configuration at die double bond (equation 73). 

The Michael addition of organometallic nucleophiles to enones in the presence of copper(I) salts produces enolates which on treatment with phenylselenenyl bromide give a-seleno ketones. For example, the reaction of the zirconium enolate of 15 with a mixture of phenylselenenyl bromide and diphenyl diselenide affords a mixture of diastereomeric (2R)- and (2V)-phenylse-leno)cyclopentanones 16 in 50% and 31 % isolated yield, respectively12. The analogous reaction with phenylselenenyl chloride gives only the tram-isomer in 27% yield formation of the cw-product is not observed12. 

Phenylselenenyl bromide is generated in silu from 80 mg (0.25 mmol) of diphenyl diselenide and 40 mg (25 mmol) of Br, in 2 mL of HOAc. To this solution are added sequentially 180 mg (0.5 mmol) of 3,17-di-acetoxy-l,3,5(10)16-estratctracnc and 100 mg of KOAc and the mixture is stirred for 1 h. The reaction is terminated by addition of 20 mL of H20 and the product extracted with EtOAc. After the usual workup and purification by preparative TLC (silica gel, hexane/EtOAc 3 1), the title compound is isolated as a white solid yield 190 mg (77%) mp 130-133°C. 

A less expensive procedure that does not require the use of a silver salt involves treatment of the alkene with phenylselenenyl bromide in acetic acid43. The formation of trans-l-acetoxy-2-(phenylseleno)cyclohexane (trans-33) best exemplifies this approach. 

Various ttan,v-l-nitro-2-(phenylseleno)cycloalkanes 60 have been prepared in moderate yield by treatment of the cycloalkene with phenylselenenyl bromide followed by addition of silver nitrite in dichloromethane/acetonitrile67, 2-Phenylseleno-l-cycloalkanols are also formed in substantial amounts when moisture is not rigorously excluded67. 

Similarly, msodium azide in trifluoromethanol or lithium azide in dimethylformamide 6 8. 

On the other hand, treatment of the 0-allyloxime 3 with phenylselenenyl bromide yielded the iminium salt 4 as a diastereomeric mixture, which was then converted into the corresponding trarts-fused perhydroquinoline 5 by reduction with sodium borohydride. The configuration of the diastereomers was assigned from 1H-NMR data251. 

On the other hand, when the allylic benzimidate 13 was treated with phenylselenenyl bromide, cyclization occurred to form the intermediate diastereomeric iminium salts 14 which were directly converted in good yield into the corresponding synjanti mixtures of amino alcohol derivatives 15. The stereoselectivity of the cyclization was determined by hydrodeselenation of the purified diastereomeric mixtures, hydrolysis of the benzoate esters and comparison of the resulting amino alcohols with authentic samples245. 

The cyclization of O-allyl oximes 1, performed with diphenyl diselenide/ammonium thiosulfate/ trifluorosulfonic acid or phenylselenenyl bromide, gave cyclic iminium salts 2 via an intramolecular antt -addition mechanism. By addition of water to the reaction mixture, 3-substi-tuted isoxazolidines 3 are formed in good yield. When the salts 2 were prepared by using phenylselenenyl bromide, A-alkyl 3-substituted isoxazolidines 4 were afforded in good yield by reduction of 2 with sodium borohydride in methanol247-249. 

Dehydrogenation of nitroalkenes was recently re 3orted by Japanese workers Sakakibara a at. [105], The reaction consists in acting witli phenylselenenyl bromide on nitroalkanes in the presence of butyMithium. Nitrophenylscleno-alkanes are formed in the first instance, and decompose under the action of hydrogen peroxide (27)... 

One of royal jelly acids (10-hydroxy-2-decenoic acid) (154) is prepared from the telomer of acetoacetate i5359) (Scheme 43). Treatment of 153 with sodium ethoxide andhydroboration lead to 10-hydroxy-4-decenoate, Then the internal double bond is reduced and then reintroduced at the conjugated position by the addition of phenylselenenyl bromide. Subsequent oxidative removal of the phenylthio group yields 154. 

Proton-induced cyclization of allylic thioamides (335) leads to 2-thiazolines (336). The cyclization can also be induced by phenylselenenyl bromide and subsequent reductive removal of the phenyl-selenenyl group (Equation (62)) <9UOC3425>. 

Phenyl neopentyl sulfide, 272 Phenyl oxime-O-sulfonates, 456 2-Phenyloxirane, 219 Phenylpropargyl aldehydes, 6 Phenylselenenyl bromide, 459-460 Phenylselenenyl chloride, 459-460 Phenylselenenyi trifluoroacetate, 459 Phenylselenlnyl chloride, 459-460 ot-Phenylseleno ketones, 459 Phenylselenol, 235, 362 Phenylsulfinylcarbene, 457... 

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