Methylselenol esters

Ketones from esters. Methylselenol esters, readily available by reaction of carboxylic esters with (CHdiAlSeCH, (8, 182), react with organocuprates to give ketones in generally high yield... 

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. 

Methylselenol esters. Methyl and ethyl carboxylic esters are converted into methylselenol esters by this reagent (0°-20°). 

Methylselenol esters, 182-183 a-Methylstilbene, 507 Methylthioacetonitrile, 349-350 Methyl thiocarbamates, 91 a-Methylthio carboxylic acids, 103, 304... 

Dimethylaluminum methylselenolate (38) is prepared in situ by the reaction of trimethylaluminum with elemental selenium in refluxing toluene [66]. The yellow-colored solution can be used in various reactions, such as the conversion of esters to the corresponding selenol esters, the ring opening of epoxides, and Michael addition to cyclohexenone (Scheme 36) [66]. 

Conversion of O-alkyl esters to their corresponding mefhylselenoesters by treatment with dimethylaluminum methylselenolate has also been reported [29]. Preparation of selenoesters directly from carboxylic acids is accomplished by reaction with selenocyanates [30] or N-PSP (N-phenylselenophthalimide) [31] in the presence of trialkylphosphine. Yields of selenoesters prepared from N-PSP and BujP are usually higher than those obtained by use of ArSeCN and BU3P (Scheme 15.9). 

Dimethylaluminium methylselenolate reacts with O-alkyl esters to provide methyl selenol esters the latter are good acyl group transfer reagents. ... 

Methyl selenoesters can be synthesized directly from alkyl esters or lactones using dimethylaluminium methylselenolate, simply prepared from tri-methylaluminium and selenium.Very good yields can be obtained, and the reagent also reacts with epoxides to give 2-methylselen-l-ols and delivers a methylseleno-group in a Michael fashion to cyclohexenone. 

Methylseleno esters are readily available in excellent yields by the reaction of Dimethylaluminum Methylselenolate with O-alkyl esters. These selenoesters will acylate reactive arenes (eq 69) and heterocyclic compounds (eq 70) when activated by CuOTf, a selenophilic Lewis acid. Of the potential activating metal salts tested, (CuOTf)2 QHe is uniquely effective. Mer-cury(ll) or copper(l) trifluoroacetates that are partially organic-soluble, as well as the corresponding chlorides, silver nitrate, and... 

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