Selenoxides from selenides

Several cyclobutenes can be synthesized by elimination of selenoxides from the corresponding methyl- or phenylselanyl derivatives 58 or by elimination of dimethyl selenide from the corresponding selenonium salts 60. The results of these conversions are summarized in Table l.23 The cyclobutenes have been used as precursors for substituted butadienes.23... 

A single enzyme is sometimes capable of many various oxidations. In the presence of NADH (reduced nicotinamide adenine dinucleotide), cyclohexanone oxygenase from Acinetobacter NCIB9871 converts aldehydes into acids, formates of alcohols, and alcohols ketones into esters (Baeyer-Villiger reaction), phenylboronic acids into phenols sulfides into optically active sulfoxides and selenides into selenoxides [1034], Horse liver alcohol dehydrogenase oxidizes primary alcohols to acids (esters) [1035] and secondary alcohols to ketones [1036]. Horseradish peroxidase accomplishes the dehydrogenative coupling [1037] and oxidation of phenols to quinones [1038]. Mushroom polyphenol oxidase hydroxylates phenols and oxidizes them to quinones [1039]. 

P-Hydroxy selenides are conveniently prepared from epoxides by treatment with sodium phenylse-lenide (Scheme 32) and by the addition of benzeneselenenic acid and its derivatives to alkenes (Scheme 33), - -" although in some cases these reactions are not regioselective. Useful phenylseleno -etherification and -lactonization reactions have been developed which can be regioselective (equation 42 and Schemes 34 and 35). -" " Selenide- and selenoxide-stabilized carbanions have been used in addition reactions with aldehydes and ketones, - and the reduction of a-seleno ketones also provides a route to P-hydroxy selenides. ... 

Alkyl halides can be prepared from selenides and selenoxides.60 Oxidations - Active manganese dioxide oxidations have been reviewed.61... 

Similarly, yn-elimination of PhSeOH from selenoxide 8 and selenoxides derived from selenides 9-11 in presence of H2O2 occurs below rt to produce enones in high yields. 

Reich has now described the ready preparation of a-lithio-selenides and -selenoxides, which smoothly condense with aldehydes and ketones. The resultant /3-hydroxy-selenides and -selenoxides can be reductively eliminated under very mild conditions to give tetrasubstituted olefins, which are not readily available from the Wittig reaction. The /3-hydroxyselenides can be converted into olefins under milder conditions than their sulphur equivalents, using methane-sulphonyl chloride in triethylamine. 

Grieco, P. A. Gilman, S. Nishizawa, M. Organoselenium Chemistry. A Facile One-Step Synthesis of Alkyl Aryl Selenides from Alcohols /. Or. Chem. 1976, 41, 1485-1486. Sharpless, K. B. Young, M. W. Olefin Synthesis. Rate Enhancement of the Elimination of Alkyl Aryl Selenoxides by Electron-Withdrawing Substituents / Or . Chem. 1975, 40, 947-949. 

A 30% solution of hydrogen peroxide in water was purchased from Mallinckrodt Chemical Works. The reaction requires 2 molar equivalents of hydrogen peroxide, the first to oxidize the selenide to the selenoxide and the second to oxidize the elimination product, benzeneselenenic acid, to benzeneseleninic acid. The submitters recommend that the hydrogen peroxide solution be taken from a recently opened bottle, or titrated to verify its concentration. 

Allylic alcohols can also be obtained from epoxides by ring opening with a selenide anion followed by elimination via the selenoxide (see Section 6.8.3 for discussion of selenoxide elimination). The elimination occurs regiospecifically away from the hydroxy group.116 117 118... 

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. 

Phenyl -tolyl selenide in aqueous suspension is boiled with potassium permanganate for several hours. The manganese mud is dissolved and the 4-carboxydiphenyl selenoxide precipitated by passing in sulphur dioxide. After filtration the precipitate is macerated with dilute sodium carbonate solution, the products of oxidation being separated in this manner into phenyl p-tolyl selenoxide and 4-carboxydiphenyl selenoxide. Addition of dilute sulphuric acid to the sodium carbonate extract causes the separation of 4-carboxydiphenyl selenoxide, which is crystallised from alcohol. The product is a microcrystalline powder, melting with decomposition at 253° to 255° C. Attempts to resolve it into optically active forms have failed the l-menthylamine salt melts at 220° to 222° C. with decomposition, and the d-a-phenyl-ethylamine salt forms feathery needles, M.pt. 194° to 195° C. with decomposition.3... 

Di-a-naphthyl selenium dibromide, (C10H7)2SeBr2, is prepared in the usual manner. It forms wThite needles, melting at 183° C. with decomposition, soluble in amyl alcohol but best recrystallised from carbon disulphide. The halogen may be removed by alkali, but only di-a-naphthyl selenide results, no selenoxide being isolated as in the preceding cases. 

Treatment of the hydronitrates in aqueous solution with sodium carbonate causes evolution of carbon dioxide. Evaporation to dryness, followed by extraction with alcohol or benzene, then yields oils which are probably the selenoxides. These oils with concentrated hydrochloric acid are converted into white solids, crystallisable from benzene, xylene, alcohol or dry ether. These solids are the dichlorides of the original selenides, and when prepared by this method their melting-points are as follows Phenyl methyl selenium dichloride, M.pt. 122° C. phenyl ethyl selenium dichloride, M.pt. 64° to 65° C. diphenyl selenium dichloride, M.pt. 142° C. 

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]. 

Certain alkylaryl selenides can be prepared by the electrophilic selenylation of eno-lates (Figure 4.12 also see Table 10.4). With a subsequent H2Oz oxidation to produce the selenoxide followed by the elimination of Ph—Se—OH, one proceeds in a total of two synthetic steps from a carbonyl or carboxyl compound to its a,/3-unsaturated analogue. 

Cyclohexyl selenides 162 can be prepared from the 4-substituted cyclohexanones via the selenoketals and upon oxidation with chiral oxidants, compounds 163 were obtained in high yields and with excellent stereoselectivities. Some representative examples are summarized in Table 5 and it is obvious that only the Davies oxidant 158 is leading to high enantiomeric excesses in the product 163 whereas under Sharpless oxidation conditions no selectivity is obtained. The titanium complex formed in the Sharpless oxidant may promote the racemization of the intermediate selenoxide by acting as a Lewis acid catalyst, while the aprotic nature of the Davies oxidant 158 slows down racemization dramatically. 

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