Selenol esters synthesis

Acyl radical cyclization to cyclohexanones.n Acyl radical cyclization to five-membered rings is well known, but this reaction is also useful for synthesis of substituted cyclohexanones as shown by a recent synthesis of the a-methylenecyclo-hexanone 3. Thus treatment of the selenol ester 1 with Bu3SnH and AIBN in C6H6 at 80° provides a 1 1 mixture of cyclohexanones 2 in 91 % yield. Oxidation of 2 with... 

Seleno esters are also produced in good yield by reactions of dimethy-laluminim methanoselenolate103 (CH3)2AlSeCH3, with the protected C-ribofuranosyl acetate 269. Treating the selenol ester 270 with either cuprous or mercuric chloride produced the (Gensler) lactone.110 271, a product useful in the synthesis of various C-nucleoside antibiotics.111,112... 

As well as thiol esters, selenol esters (1) frequently exhibit a high and selective reactivity toward nucleophiles, which is enhanced even further by activation with heavy ions or oxidizing agents. These properties make selenol esters valuable acyl transfer agents. This review deals with general methods for the synthesis of selenol esters and their reactivity as acyl transfer agents. Furthermore, selenoesters (2), isomeric compounds of selenol esters, and their derivatives selenoamides (3) are also described. These compounds show the characteristic reactivity based on the carbon-selenium double bond. 

Alkali metal salts of selenol can also be used in the synthesis of selenol esters. Axial and equatorial selenol esters of cholestane and androstanone have been prepared from the potassium salt (7) and benzoyl chloride (Scheme 2 illustrates the axial isomer). ... 

As well as acylation of selenols, alkylation of selenocarboxylates with alkyl halides is one of the most straightforward methods for synthesis of selenol esters. However, known examples of selenol esters synthesized using this strategy have been limited to a few cases, due to the difficulty of the preparation of selenocarboxylates. 

One of the most general methods for synthesis of selenol esters uses dimethylaluminum methylseleno-late (16), which has been found to be a remaiicably efficient and versatile reagent for the conversion of O-alkyl esters to their corresponding methylselenol esters under mild conditions. The reagent (16) is conveniently prepared by heating a toluene solution of trimethylaluminum with powdered selenium for 2 h under reflux. TTie transformation of various esters to selenol esters can be completed within 1 h. Representative results are shown in Scheme 6 (17-23). This method can also be applied to cyclic esters U ) and esters (20)-(23) containing other functional groups. 

A new method for the transformation of —CO2H to —H has been attained by formation of the selenol ester from carboxylic acid, followed by its reduction. Owing to high chemoselectivity and mild reaction conditions, this method is often utilized for the synthesis of natural products (equation 21). ... 

Synthesis of a,p-Unsaturated Selenol Esters and Vinylic Selenol Esters... 

This protocol is applicable to the synthesis of selenol esters starting from selenoacetylenes 11 (Eq. 11) [15b, 16]. 

Seleno-carboxylic acid esters (selenol esters) 2 are also prepared like thiol esters by the reaction of acyl halides with selenols, or diselenides as well as their alkali metal salts. Most of the preparative methods for thiol esters shown in Sect. 2.1 are applicable to the synthesis of selenol esters 2. Unique synthetic... 

In 1980, Detty and co-worker revealed the synthesis of selenol esters by the reaction of thallous phenyl selenide with aroyl and acyl halides (Eq. 35) [70]. 

Segi, Sonoda and co-workers reported a one-pot synthesis of selenol esters by tandem alkylation-acylation of bis(trimethylsillyl) selenide 52 as a Se " equivalent (Scheme 14) [78]. 

Scheme 15 Synthesis of selenol ester by the use of Se/C0/H20 reaction system...

Scheme 16 Synthesis of a,p-unsaturated selenol esters by the use of zirconene hydrochloride...

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