Phenylseleno ketones

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. 

Photolytic allylation of a-phenylseleno ketones.5 a-Phenylselenocycloalka-nones on irradiation with allyltributyltin undergo coupling to give a-allylcyclo-alkanones in generally good yield (equation I). 

Reaction with ketones. The reagent reacts with ketones in ether to introduce a C6H5SeCl2 group into the a-position. The products undergo selenoxide elimination to give a,0-enones they are reduced by thiourea to a-phenylseleno ketones. 

Allylphenyl selemdes.3 a-Phenylseleno ketones react with trimethylsilylmethyllithium to afford an adduct that on treatment with a catalytic amount of SnCl2 loses the elements of (CH3)3SiOH accompanied with a 1,3-migration of the phenylselenyl group to give a primary allyl phenyl selenide. 

Phenylpropane-l-ol, 438 Phenyl propargyl seienide, 365 Phenylselenoacetaldehyde, 365-366 a-Phenylseleno aldehydes, 25, 29 up-Phenylselenocarboxylic acids, 496 Phenylselenoetherification, 26 a-Phenylseleno ketals, 29 a-Phenylseleno ketones, 25 Phenylselenolactones, 26 Phenylselenomethyl ketones, 365-366 N -Phen y Iselenopht halim ide, 366-367 N-Phenylselenosuccinimide, 366-367 Phenylselenotrimethylsilane, 373 Q -Phenylseleno-Q ,/3-unsaTurated ketones, 28... 

Scheme 34. Seleno-Transfer Carbocyclizations of a-Phenylseleno Ketones...

Note that the relative insensitivity of sulfur toward nucleophilic attack allows the selective deselena-tion of thioselenoketals. On the other hand, ketones are tolerated by PhSeLi, a useful property for che-moselective deselenations of a-phenylseleno ketones (Scheme 20). ... 

The most useful method is reaction of ketone (and ester) hthium enolates, usually prepared by deprotonation of ketones with LDA, with either Ce H5 SeBr or Ce Hs SeCl. Enol acetates can be converted into a-phenylseleno ketones by reaction with phenylselenenyl trifluoroacetate, prepared in situ by treatment of CeHsSeCl or CeHsSeBr with silver trifluoroacetate or by conversion to the lithium enolate and reaction with CeHsSeBr. It is sometimes possible to obtain isomeric a-phenylseleno ketones by use of these two methods (equations 1 and II). 

The selenoxide elimination reaction proceeds in satisfactory yield in the case of acylic a-phenylseleno ketones and of cyclic a-phenylseleno ketones in which the carbon bearing the selenium is fully substituted. 

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... 

Phenylselenoalkenes, 25-26 a-Phenylseleno carbonyl compounds, 28 Phenylseleno-l-dodecene, 294 Phenylselenoetherification, 26-28 Phenylselenoimines, 29-30 a-Phenylseleno ketones, 26, 209 Phenylsclcnolactonization, 26... 

The treatment of a,p-unsaturated ketones with organocopper reagents provides another method to access specific enolates of unsymmetrical ketones. Lithium dialkylcuprates (see Section 1.2.1) are used most commonly and the resulting enolate species can be trapped with different electrophiles to give a,p-dialkylated ketones (1.27). Some problems with this approach include the potential for the intermediate enolate to isomerize and the formation of mixtures of stereoisomers of the dialkylated product. The intermediate enolate can be trapped as the silyl enol ether and then regenerated under conditions suitable for the subsequent alkylation. Reaction of the enolate with phenylselenyl bromide gives the a-phenylseleno-ketone 12, from which the p-alkyl-a,p-unsaturated ketone can be obtained by oxidation and selenoxide elimination (1.28). 

The asymmetric reduction of y-phenylseleno ketones and the intramolecular substitution of the phenylselenone residue by the oxygen atom of a hydroxy group led to 2-substituted tetrahydrofurans (13OL3906). Polysubstituted furans were formed in the photoredox neutral coupling of alkynes with 2-bromo-1,3-dicarbonyl compounds. The reaction was carried out without any external stoichiometric oxidants (130L4884). 

---