Phenyl selenoester

In another procedure, acyl radicals derived from phenyl selenoesters ArCOSePh I by treatment of them with Bu3SnH) add to a,P-unsaturated esters and nitriles to give y-keto esters and y-keto nitriles, respectively. ... 

Phenyl selenoesters have been reported to undergo reduction to the corresponding aldehydes and/or alkanes in the presence of (TMS)3SiH under free-... 

Phenyl selenoesters have been reported to undergo reduction to the corresponding aldehydes and/or alkanes in the presence of (TMS)3SiH under free-radical conditions16. The decrease of aldehyde formation through the primary, secondary and tertiary substituted series, under the same conditions, indicated that a decarbonylation of acyl radicals takes place. Equation 11 shows an example of a tertiary substituted substrate. 

Boger and Mathvink [134] recently reported the generation of acyl radicals from phenyl selenoesters and their participation in macrocyclization through free-radical alkene addition reactions. As shown in Scheme 73, the 16-membered macrocycle 222 was obtained from phenyl selenoester 221 in 68% yield. 

Methyl selenoesters can be simply obtained by treating alkyl esters with the aluminium-based reagent Me2AlSeMe at 0-20 "C, and a rather neat method has been developed for obtaining phenyl selenoesters from (hindered) carboxylic acids. 

S-phenyl thiobenzoate typical procedure in the presence of diphenyl disulphide. Photolysis of the telluroester (Ar = 4-FCgH4) in the presence of 6 equiv of diphenyl disulphide according to the standard for the formation of selenoesters gave 71% of the thiobenzoate after chromatography on silica gel (eluent hexane/ ethyl acetate, 9 1). The product had a melting point and spectral characteristics in accordance with those described in the literature. 

Although the photochemistry of aryl selenoesters and aryl telluroesters is not fully developed, there are some photoreactions of these compounds that resemble a photo-Fries process. Se-/ ara-tolyl selenobenzoate (212) gives, upon irradiation, selenocresol (214), benzaldehyde, and the benzophenone 213 (Scheme 56), which is clearly a photo-Fries product [157,158], Starting from Se-phenyl 2-chlorosele-... 

Preliminary work with model selenoester 54 revealed that the hexabutyldistannane protocol, previously used in the phenyl and pyridine series, now gave poor yields of cyclized products. However, treatment of 54 under reductive TTMSS conditions in the presence of AIBN as the initiator led to the calothrixin-related pentacycle 55 in 65% yield. This compound, which incorporated the 2-cyano-2-propyl moiety of the initiator, was converted into A -methylcalothiixin 56 by treatment with potassium hydroxide in methanol, through a process involving a gramine-type nucleophilic substitution and the oxidation of the resulting carbinol by air. 

Although less common, some examples of PFR with thioesters, selenoesters, and telluroesters have also been reported [102-105]. Thus, irradiation of S-phenyl thioacetate gives minor amounts of ortho- and para-rearranged products escape of the phenylthio radical out of the cage predominates. 

Thioesters, Selenoesters, and Thioamides.—Commercially available phenyl dichlorophosphate has been reported to be a superior reagent to MV-dimethyl-phosphoramidic dichloride (4, 244) for the preparation of thioesters directly from carboxylic acids and thiols. Carboxylic acid chlorides can be efficiently converted into thioesters by reaction with adducts formed between thiols and l-methylpyridine-3,5-dicarboxylates. Alternatively, copper(i) mercaptides, formed from thiols and CuaO, or thallous thiophenoxide can be used. The latter method can also be used to prepare selenoesters as well as a-phenylthio-and a-phenylseleno-acids and esters from a-halo-acids and a-halo-esters, respectively. 

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