3- Hydroxyalkyl selenides

Alcohols with organoelement groups listed in Table 13 gave with one exception only small amounts of olefine. But with hydroxyalkyl-selenides (35a, G = -SePh or -SeCHs) stereospecific frans-elimination can be achieved in acidic (for instance excess of perchloric acid ether at room temperature) or basic media to give olefines in good yield So we can state that preparatively useful carbonyl olefination reactions in which epoxides are not a by-product, are allowed not only with phosphorus and silicium containing regents but are possible in the wide area of the periodical table marked in Scheme 55c with little lines. 

Alkyltin compounds carrying a leaving group at the y-position undergo 1,3-elimination to produce cyclopropanes9. y,<5-Epoxyalkyltin derivatives are converted to cyclopropyl-methyl alcohols under catalysis of a Lewis acid (equation 5)10. y-Hydroxyalkyl selenides... 

Another possible synthesis is offered by the reaction of alkoxy- or aryloxysulfonylisocyanate to epichloridrine derivatives. The intermediate carbamate easily cyclises upon heating in acetone <07SC2215>. Alternatively phenyl 2-hydroxyalkyl selenides can react with benzoyl isocyanate and the final carbamate cyclize after oxidation of the selenyl functionality <07SC2693>. 

Treatment of selenurane oxide 20 with Z equiv of triphenylphosphine caused ring opening to the symmetrical hydroxyalkyl selenide 103 (Scheme 4) <2002HAC437>. 

Hydroxyalkyl Selenides as Precursors of Epoxides and Carbonyl Compounds... 

Mechanism of epoxide and ketone formation from B-hydroxyalkyl selenides... 

Synthetic Uses of Hydroxyalkyl Selenides Comparison with Well-established Related Reactions... 

Further reaction of Aese species with carbonyl compounds and hydrolysis of the resulting alkoxide leads to p-oxidoalkyl selenoxides which have been transformed into allyl alcohols on thermal decomposition (Schemes 51, 52 and 54, entry a see Section 2.6.4.4) or reduced to p-hydroxyalkyl selenides or to alkenes (Scheme 53). P-Oxidoalkyl selenoxides derived from cyclobutanones react in a different way since Aey rearrange to cyclopentanones upon heating (Scheme 54, b. Schemes 120 and 121 and Section 2.6.4.5.3). 

The organometallics bearing a selenium atom directly attached to the carbanionic center, the synthesis of which has been discussed above, have been reacted with a large variety of electrophiles. - - 12,13,16,17 Among these electrophiles, aldehydes and ketones occupy a place of choice, usually leading, after hydrolysis, to 3-hydroxyalkyl selenides. Some examples are gathered in Schemes 112 to 118. 

Hydroxyalkyl selenides have been transformed to epoxides (see Section and to... 

The reactions of a-selenoalkyllithiums with aliphatic and aromatic aldehydes and ketones are not usually stereoselective regardless of the solvent used (ether or THF). Even in the most favorable cases, such as that of l-methylseleno-2,2-dimethylpropyllithium and heptanal, in which well-diffeiendated bulky groups are involved, the stereoisomeric ratio ranges from 1 1 to 3 2 (Scheme 124). - However, in the case shown in Scheme 86, b, in which the lithium can coordinate to the silyloxy group, only one of the two stereoisomeric 3-hydroxyalkyl selenides is formed. 

The reaction takes another course with chalcone since a mixture of -hydroxyalkyl selenides and 7-selenoalkyl phenyl ketones resulting from C-1 and C-3 attack, respectively, is produced (Scheme 135, compare b and c with a). This enone is the only one among those tested to react in such a way. Interes-... 

The reduction of (3-hydroxyalkyl selenides to alcohols has been achieved - - - by lithium in ethylamine (Scheme 161, a Scheme 162, a Scheme 163, a Scheme 167) or triphenyl- or tributyl-tin hydride in toluene, with or without AIBN. Most of these reactions proceed through radicals. The reactions involving tin hydrides can be carried out thermally around 120 or photochemically at much lower temperature (0-20 The cleavage of the C—SePh bond is faster than that of the... 

P-hydroxyalkyl selenides bearing two alkyl substituents at the selenium-bearing carbon, a tendency to produce rearranged compounds besides the expected alkenes (Scheme 165, a). These become the exclusive compounds obtained - when l-seleno-l-(r-hydroxyalkyl)cyclopropanes are involved (Schemes 132, a Scheme 163, f-h). This behavior is general for almost all cyclopropylcarbinols bea g a heterosubstituent (e.g. OR, NR2, SR, SeR) at that position on the cyclopropane ring (see Section 2.6.4.5.3).>2... 

The presence of two potential leaving groups p to each other makes p-hydroxyalkyl selenides valuable candidates for epoxide synthesis, as well as for pinacol-type rearrangement These concurrent transformations, which usually require the selective activation of the selenyl moiety to a better leaving... 

The reaction involving the alkylation of p-hydroxyalkyl selenides to give p-hydroxyalkylselenonium salts which are then cyclized with a base is by far the most general. It allows Ae synthesis of a large variety of epoxides such as tenninal, a,a- and a,p-disubstituted, tri-33-> and tetra-substituted, 3,i88 as oxaspiro[2.0.n]-hexanes, -heptanes and -octanes (Scheme 161, g Scheme 162, d Scheme 164, d Scheme 165, b) - and vinyl oxiranes (Schemes 166 and 181)33 -239 from both p-hydroxy-alkyl methyl33- 3 3 22>.222j36,263 phenyl selenides. ... 

The most successful combination involves methylseleno derivatives as starting materials, methyl iodide (neat) as the alkylating agent and 10% aqueous potassium hydroxide solution in ether as the base. In some difficult cases, such as those involving hindered p-hydroxyalkyl selenides, where the... 

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