Selenides, 3-hydroxy oxidation

Oxidation of -hydroxy selenides.s p-Hydroxy selenides (1), obtained by reaction of a dialkyl ketone with phenylselenenylrnethyllithium, are oxidized by... 

Formation of CK-configurated cyclobutanones has also been observed with 2-methylcyclopen-tanone and 2-methylcyclohexanone/8 However, stereoreversed eyclobutanone formation can be achieved by opening the intermediate oxaspiropentane with sodium phenyl selenide, oxidation of the resulting / -hydroxy selenide with 3-chloroperoxybenzoic acid and subsequent rearrangement in the presence of pyridine/18 Thus, from one oxaspiropentane 8, either stereoisomeric eyclobutanone cis- or lrans-9 was produced. The stereoreversed eyclobutanone formation proceeds from a stereohomogenous / -hydroxy selenoxide and is thought to be conformationally controlled. 

The product of the oxidation of 2-butene with oxygen in the presence of bis (l-methyl-2-acetoxypropyl) selenide was 3-acetoxy-l-butene in acetic acid as solvent and 3-hydroxy-l-butene(a-methylallyl alcohol) in aqueous dioxane. The reaction rate depends on the selenide concentration. 

Selenones/ y-Hydroxy vinyl selenides (1) are labile and readily undergo dehydration on standing, but can be oxidized successfully to y-hydroxy vinyl selenones (2) by m-chloroperbenzoic acid in the presence of K2HP04 in CH3OH at 25°. 

The cyclohexene 121, which was readily accessible from the Diels-Alder reaction of methyl hexa-3,5-dienoate and 3,4-methylenedioxy-(3-nitrostyrene (108), served as the starting point for another formal total synthesis of ( )-lycorine (1) (Scheme 11) (113). In the event dissolving metal reduction of 121 with zinc followed by reduction of the intermediate cyclic hydroxamic acid with lithium diethoxyaluminum hydride provided the secondary amine 122. Transformation of 122 to the tetracyclic lactam 123 was achieved by sequential treatment with ethyl chloroformate and Bischler-Napieralski cyclization of the resulting carbamate with phosphorus oxychloride. Since attempts to effect cleanly the direct allylic oxidation of 123 to provide an intermediate suitable for subsequent elaboration to ( )-lycorine (1) were unsuccessful, a stepwise protocol was devised. Namely, addition of phenylselenyl bromide to 123 in acetic acid followed by hydrolysis of the intermediate acetates gave a mixture of two hydroxy se-lenides. Oxidative elimination of phenylselenous acid from the minor product afforded the allylic alcohol 124, whereas the major hydroxy selenide was resistant to oxidation and elimination. When 124 was treated with a small amount of acetic anhydride and sulfuric acid in acetic acid, the main product was the rearranged acetate 67, which had been previously converted to ( )-lycorine (108). 

Unlike Af-hydroxy-2-thiopyridone, TV-hydroxy-2-selenopyridone is rather unstable and is easily oxidized. However, once photolytic treatment of O-acyl ester (53) of AMiydroxy-2-selenopyridone is carried out, the formed 2-pyridyl selenide is very useful. Thus, elimination of the selenoxides, formed from the oxidation of the selenide with mCPBA or ozone, proceeds effectively at low temperature. For example, eq. 8.23 shows the preparation of (l)-vinylglycine (56) from (L)-glutamic acid without racemization at all [70]. 

Anilino-4-methyl- -2-oxid E2, 662, 784 -Anilino-4-meth yl- -2-selenid K2, 784, 787 -Anihno-4-methyl- -2-sulfid E2, 662 -Benzoyl-4-methyl- -2-oxid E2, 382 -Benzyl-5,5-bis-[chlormethylJ- -2-oxid E2, 367 -Benzyl-5-chlormethyl-5-ethyl- -2-oxid E2, 367 -(Bis- 2-chlor-ethyl]-amino)-5,5-bis-[hydroxy-methyl]- -2-oxid XII/2, 415 2-(Bis-[2-chlor-ethyl]-amino)- -2-oxid XII/2, 415... 

Bipheny]yl)- E2, 838 5-Hydroxy- -5-oxid XII/1, 240 5-(Methy]-phenyl-iminio)-5-phenyl- E2, 889 5-Phenyl- E2, 892 5-Phenyl- -9-selenid E2, 93... 

N-Sulfonyloxaziridines are an important class of selective, neutral, and aprotic oxidizing reagents.11 Enantiopure N-sulfonyloxaziridines have been used in the asymmetric hydroxylation of enolates to enantiomerically enriched a-hydroxy carbonyl compounds,9 11-13 the asymmetric oxidation of sulfides to sulfoxides,14 1S selenides to selenoxides,16 sulfenimines to sulfinimines,17 and the epoxidation of alkenes.18... 

Cyclic ethers from dienes, The reagent 1 reacts with 1,5-cyclooctadiene in CH2CI2 at 25° to give 2 in 90% yield. Presumably the first step is addition of 1 to one double bond to form a jS-hydroxy selenide, which undergoes further reaction with 1 to form the cyclic ether 2. The product can be converted to 3 or to 4 by oxidation or reduction. 

Oxyselenation ofalkeues, - Treatment of olefins with 1 or 2, water, and an acid catalyst (e.g., p-TsOH) in CH2CI2 affords j3-hydroxy selenides in excellent yield. Unsaturated carboxylic acids, phenols, alcohols, thioacetates, and urethanes react with 1 or 2 and an acid catalyst ( —78- 25°) to afford products of oxidative cyclization. These reagents are superior to benzeneselenenyl halides for selenium-induced ring closures. This reaction is also useful for synthesis of 14- and 16-membered lactones. Benzeneselenenyl halides and benzeneselenenic acid do not promote macrolide formation under similar conditions. 

Phenylselenomethyl ketones. The reagent reacts with Grignard reagents to form /8 -hydroxy selenides (2), generally in 80-90% yield. Oxidation of the selenides to the desired phenylselenomethyl ketones (3) proved to be more difficult than anticipated. In the case of saturated alcohols, the Corey-Kim reagent (4, 87-90) is satisfactory. Allylic alcohols are best oxidized with DDQ. 

In the stereoselective synthesis of ( + ) and (-)-litsenolideC, (l)17-18 oxidation and subsequent sigmatropic rearrangement of an a-substituted allylic selenide, in which the double bond was incorporated in a lactone ring, were used for the construction of the stereogenic center bearing the hydroxy group and the exocyclic Z double bond. 

Entries 1 and 2 in Table 8 are examples of an overall antarafacial 1,3-transposition of a hydroxy group by selenium compounds20,21. Treatment of the alcohols with 2-nitrophenyl seleno-cyanate in the presence of tributylphosphine gave the selenide with inversion of configuration. Oxidation with hydrogen peroxide led to the selenoxide, which rearranged suprafacially to the allylic alcohol. 

Epoxide opening by benzeneselenolate anion gave the rphenyl selenide with high regioselectivity (Table 8, entry 4)22. Oxidation and rearrangement yielded (+)- ra/t. -2-cyclohexene-1,4-diol. A similar approach was the key step in the synthesis of a ( + )-chorismate-prephenate analog (Table 8, entry 5)24. 

Selenolactonization of ( )-2,4-cyclohexadieny acetic acid with phenylselenenyl chloride occurred exclusively in a 1,4-(fl ri)-fashion with high stereoselectivity. The resulting selenide underwent rearrangement after oxidation to the stereochemically defined cts-lactone with a tram-hydroxy group25 27. 

In the synthesis of functionalized eudesmanolides only the product with a /i-onentated hydroxy group was found after oxidation of the selenide with peracetic acid37. 

The oxidative rearrangement of racemic ira .v-2-hydroxy-5-cyclohexenylphenyl selenide gave the t/-[Pg.1198]

The stereospecific conversion of cyclohexene into the corresponding amido selenide 54 is illustrated in Scheme 8. These amidoselenenylation reactions are commonly employed for the preparation of allylic and saturated amides by oxidative or reductive deselenenylation. Propionitrile, butyronitrile, benzonitrile and ethyl cyanoacetate may be used in place of acetonitrile. Styrene gave poor results and other electron-rich olefins such as 1-methylcyclohexene or 2,3-di-methylbut-2-ene did not give the amidoselenenylation products. The reaction can also be effected starting from the hydroxy- or methoxyselenenylation products of alkenes, in the presence of water and trifluoromethanesulfonic acid in this case the nitriles are used in stoichiometric amounts [48c]. This methodology was employed to prepare the amidoselenenylation products of styrene, 55, and of electron-rich olefins. It was necessary, however, to replace the phenyl-... 

Several oxaziridines related to (14) (eq 8) have been used, most notably in the enantioselective oxidation of sulfides to sulfoxides, of selenides to selenoxides, and of alkenes to oxiranes, It is also the reagent of choice for the hydroxylation of lithium and Grignard reagents and for the asymmetric oxidation of enolates to give a-hydroxy carbonyl compounds, - A similar chiral fluorinating reagent has also been developed, ... 

Several of the procedures discussed in the sulfoxide section describe the successful extension of the method to the reduction of selenoxides, - - and there is little doubt that many of the other procedures cited earlier could be used likewise. Sakaki and Oae used triphenylphosphine selenide and similar se-lenides to reduce selenoxides to selenides in 79-93% yield (equation 19). Using a chiral phosphine selenide, these workers showed that the phosphine oxide formed had suffered predominant inversion, with a stereospecificity of over 80%. Detty has reported the application of the silane PhSeSiMes (12) to the reduction of selenoxides and telluroxides. The reactions are rapid and proceed essentially quantitatively, even in the presence of a hydroxy or carbonyl group. 

The spectrum of applications of potassium permanganate is very broad. This reagent is used for dehydrogenative coupling [570], hydrox-ylates tertiary carbons to form hydroxy compounds [550,831], hydroxylates double bonds to form vicinal diols [707, 296, 555, 577], oxidizes alkenes to a-diketones [560, 567], cleaves double bonds to form carbonyl compounds [840, 842, 552] or carboxylic acids [765, 841, 843, 845, 852, 869, 872, 873, 874], and converts acetylenes into dicarbonyl compounds [848, 856, 864] or carboxylic acids [843, 864], Aromatic rings are degraded to carboxylic acids [575, 576], and side chains in aromatic compounds are oxidized to ketones [566, 577] or carboxylic acids [503, 878, 879, 880, 881, 882, 555]. Primary alcohols [884] and aldehydes [749, 868, 555] are converted into carboxylic acids, secondary alcohols into ketones [749, 839, 844, 863, 865, 886, 887], ketones into keto acids [555, 559, 590] or acids [559, 597], ethers into esters [555], and amines into amides [854, 555] or imines [557], Aromatic amines are oxidized to nitro compounds [755, 559, 592], aliphatic nitro compounds to ketones [562, 567], sulfides to sulfones [846], selenides to selenones [525], and iodo compounds to iodoso compounds [595]. 

Diphenyl diselenide has been used to convert alkenes into 2-acetoxy, 2-methoxy, and 2-hydroxy selenides by indirect oxidation in MeCN-H20, MeOH, and HOAc, respectively, in the presence of Et4NX(X = Cl, Br, I) as supporting electrolytes [57]. High regio-selectivities (Markownikoff-type adduct) are observed, and best current efficiency is obtained for X = Cl or Br. Examples are shown in Eq. (26). 

Procedures which utilize selenides are similar, but a-lithio selenides are not generally preparable via simple deprotonation chemistry, due to facile selenium-lithium exchange. - Selenium-stabilized anions are available, however, by transmetalladon reactions of selenium acetals and add readily to carbonyl compounds. The use of branched selenium-stabilized anions has been shown to result exclusively in 1,2-addidon to unhindered cyclohexenones, in contrast to the analogous sulfur ylides. The resulting 3-hydroxy selenides undergo elimination by treatment with base after activation by alkylation or oxidation (Scheme 10). An alternative method of activating either p-hydroxy selenides or sulfides toward elimination involves treatment of a chloroform solution of the adduct with thallium ethoxide (Scheme 11). A mechanism involving the intermediacy of a selenium ylide is proposed. 

Selenoxide elimination is now widely used for the synthesis of a,p-unsaturated carbonyl compounds, allyl alcohols and terminal alkenes since it proceeds under milder conditions than those required for sulfoxide or any of the other eliminations discussed in this chapter. The selenoxides are usually generated by oxidation of the parent selenide using hydrogen peroxide, sodium periodide, a peroxy acid or ozone, and are not usually isolated, the selenoxide fragmenting in situ. The other product of the elimination, the selenenic acid, needs to be removed from the reaction mixture as efficiently as possible. It can disproportionate with any remaining selenoxide to form the conesponding selenide and seleninic acid, or undergo electrophilic addition to the alkene to form a -hydroxy selenide, as shown in... 

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