O-Nitrophenyl selenides

Olefin synthesis from the 5yn-oxidative elimination of o-nitrophenyl selenides, which may be prepared using o-nitrophenyl selenocyanate and BU3P, among other methods. 

Alkyl o-nitrophenyl selenides. These selenides can be prepared directly in high yield from primary alcohols and o-nitrophenyl selenocyanale in THE or pyridine at 20° in the presence of tri- -butylphosphinc (equation I). Yields arc somewhat lower for secondary alcohols. 

En route to a total synthesis of the anticancer compound FR901464, Koide and coworkers carried out a diastereoselective allylic selenoxide rearrangement upon oxidation of either allyl selenide 251 [Scheme 18.641. Optimization studies using the preformed allyl selenide 251 identified the o-nitrophenyl selenide as an effective aryl substituent and N,N-dimethylaminopyridine as the best selenophilic base additive in the formation of rearrangement product 252 (see top of Scheme 18.641. Reactions were slower and diastereoselectivity, a crucial parameter here, was lower using other bases or with less than 3 equiv of DMAP. Using the optimized conditions, a one-pot method for overall 1,3-allylic alcohol transposition was... 

Second, among the newer methods developed to effect the elimination to produce the least substituted alkene is one that involves converting the alcohol to a selenium derivative. In this procedure, a primary alcohol is treated with o-nitrophenyl sele-nocyanate in a suitable solvent such as (THF, oxacyclopentane) in the presence of a phosphine (such as tri-n-butylphosphine [(CH3CH2CH2CH2)3P]) to produce the primary alkyl selenide (Scheme 8.74). Then, in a second step, the primary alkyl o-nitrophenyl selenide is oxidized with hydrogen peroxide to yield the corresponding selenoxide, which readily undergoes elimination to the alkene. Scheme 8.74 shows the application of the sequence of reactions described above to cyclohexylmethanol and the resulting formation of the exo-methylenecyclohexane. 

Alcohols can be converted to o-nitrophenyl selenides by reaction with o-nitrophenyl selenocyanate and tri-n-butylphosphine. ... 

Azides [e.g. (+)-neomenthyl azide no physical data reported] are formed efficiently by inversion, from the corresponding alcohols and diphenylphosphoryl azide, in the presence of triphenylphosphine and diethyl azodicarboxylate [which has also been used for esterification with inversion (Vol. 5, p. 334) for a related esterification of (—)-menthol see ref. 119] a conceptually similar synthesis also yields (+)-neomenthyl azide. Cyanoselenenylation of aldehydes and of alcohols has been reported thus treatment of geraniol with o-nitrophenyl seleno-cyanide-Bu sP-THF yields the selenide (19) which can be converted into the... 

The effects of aryl groups were kinetically analyzed by comparing the rate constants of both steps (ki for oxidation step and /C2 for elimination step) which were determined by NMR analysis of the concentration of vinyl selenides, the intermediate selenoxide, and allenic sulfones [16b]. This kinetic study indicates that the rates of both oxidation and elimination steps were accelerated by the introduction of an electron-withdrawing group. Such acceleration has been known in the overall selenoxide elimination as well as in the selenoxide elimination step of alkyl aryl selenides. As a result, it was disclosed that the ratio of these rate constants (/C1//C2) was closely related to the enantiomeric excess of the products the smaller the ratio, the larger the enantiomeric excess becomes. Thus, the introduction of o-nitrophenyl group as an aryl moiety, which suppresses sterically the racemization of the intermediate chiral selenoxide and accelerates the selenoxide elimination step, is necessary to achieve a higher asymmetric induction. 

The oxidative elimination of primary selenides, readily available from the corresponding alcohol by treatment with an arylselenocyanate and tributylphosphine, is an attractive approach to the synthesis of terminal alkenes." However these reactions are relatively slow when compared with other selenoxide eliminations allowing side reactions, in particular the addition of the areneselenenic acid to the newly formed double bond (Scheme 23), to compete. It has been found that arylselenides with electron-withdrawing substituents fragment more readily, giving improved yields of products, in particular the use of o-nitrophenyl and 2-pyridyl selenides has been recommended (Scheme 37). Often for the elimina-... 

Scheme 8.74. The formation of a terminal alkene by an elimination reaction sequence that begins with the conversion of the oxygen of cyclohexylmethanol to a good leaving group through a reaction with tri- -butylphosphine and o-nitrophenyl selenocyanate to form the corresponding selenide (where the oxygen of the starting alcohol has been replaced with the aryl-substituted selenium). Subsequent oxidation to a selenoxide is followed by a rapid elimination to the desired alkene (methylenecyclohexane).

Alcohols can be converted to o-nitrophenylselenides by reaction with o nitrophenyl selenocyanate and tri(rt-butylphosphine). Several oxidants have been employed to convert selenides to selenoxides and bring about elimination. Hydrogen peroxide, sodium metaperiodate, peroxycarboxylic acids, tert bnty hydroperoxide, and ozone have been used most frequently. 

Allyldiethylamine behaves similarly, but the yields are low since neither the starting amine nor the products are stable to the reaction conditions. For the efficiency of the cyclopropanation of the allylic systems under discussion, a comparison can be made between the triplet-sensitized photochemical reaction and the process carried out in the presence of copper or rhodium catalysts whereas with allyl halides and allyl ethers, the transition metal catalyzed reaction often produces higher yields (especially if tetraacetatodirhodium is used), the photochemical variant is the method of choice for allyl sulfides. The catalysts react with allyl sulfides (and with allyl selenides and allylamines, for that matter) exclusively via the ylide pathway (see Section 1.2.1.2.4.2.6.3.3. and Houben-Weyl, Vol. E19b, pll30). It should also be noted that the purely thermal decomposition of dimethyl diazomalonate in allyl sulfides produces no cyclopropane, but only the ylide-derived product in high yield.Very few cyclopropanes have been synthesized by photolysis of other diazocarbonyl compounds than a-diazo esters and a-diazo ketones, although this should not be impossible in several cases (e.g. a-diazo aldehydes, a-diazocarboxamides). Irradiation of a-diazo-a-(4-nitrophenyl)acetic acid in a mixture of 2-methylbut-2-ene and methanol gave mainly l-(4-nitrophenyl)-2,2,3-trimethylcyclo-propane-1-carboxylic acid (19, 71%) in addition to some O-H insertion product (10%). ... 

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