Hydroxy halides, alkylation from oxides

Acidic conditions for hydroxy deprotection can be avoided if benzyl-type ethers ate used as the blocking functions. They can be prepared from the alcohols by alkylation with benzyl halide/sodium hydride in DMSO or benzyl halide/silver(I) oxide in DMF (the silver salt does not cause acyl migration as a side... 

Interaction between alkyl halides and trialkylarsine oxides generally yields a hydrogen halide adduct, 2R3AsO,HX, with liberation of an olefin, but with triethylarsine oxide and either methyl or benzyl iodide a hydroxy iodide is produced. A similar intermediate (132) has been isolated from experi-... 

An alternative route to sulphones utilizes the reaction of the appropriate activated halide with sodium dithionite or sodium hydroxymethanesulphinite [6], This procedure is limited to the preparation of symmetrical dialkyl sulphones and, although as a one-step reaction from the alkyl halide it is superior to the two-step oxidative route from the dialkyl sulphides, the overall yields tend to be moderately low (the best yield of 62% for dibenzyl sulphoxide using sodium dithionite is obtained after 20 hours at 120°C). The mechanism proposed for the reaction of sodium hydroxymethanesulphinite is shown in Scheme 4.20. The reaction is promoted by the addition of base and the best yield is obtained using Aliquat in the presence of potassium carbonate. It is noteworthy, however, that a comparable yield can be obtained in the absence of the catalyst. The reaction of phenacyl halides with sodium hydroxy-methane sulphinite leads to reductive dehalogenation [7]. 

Cyclohexene oxide and its 3-hydroxy derivatives have been opened regio- and stereospecifically with phosphodiesters. The mechanism of the reaction of oxiranes with sodium dialkyl phosphite and diphenylphosphines has been studied. Cyclopropanecarboxylic acid derivatives have been obtained from substituted oxiranes with triethylphosphonoacetate anion.The mechanism of formation of isomeric alkoxyalkylacetates from oxiranes with alkyl halides and mercuric acetate has been discussed. ... 

The spiro-dihydrofuran (61) is converted into the cyclobutane derivative (62) under the influence of trifluoroacetic acid. The lithium dienolate (64), derived from the furanone (63), yields solely y-alkylated products on treatment with alkyl halides. Thermolysis of the t-butylperoxybutenolide (65) produces about equal amounts of the hydroxy-furanone (67) and the indenone (68), presumably via the oxide radical (66). Attack of iodide ion on the salt (69) results in the formation of methyl iodide, butanolide, and (surprisingly) methyl 4-iodobutanoate. A description of a study of the photochemical rearrangement of the tetrahydrofurans (70) to the bicyclic oxetans (71) has been presented. ... 

A patent for the preparation of quaternary salts of papaverine from C5, Ce, and Cg halides been published. N-Alkyl-papaverinium salts have been found to undergo oxidation by oxygen either photolytically or in the presence of cuprous chloride, to give the isoquinolones (25). The corresponding dihydro-papaverinium salts (26), with oxygen and cuprous chloride, do not suffer fission, and oxidation of the N-methyl compound (26 R = Me) in this way, followed by reduction of the product with sodium borohydride, affords a- and -hydroxy-laudanosines 21) The n.m.r. spectrum of laudanosine has been studied in detail. 

A variation of the Wittig reaction that can overcome problems with the stereochemical outcome is the Homer-Wittig reaction with phosphine oxides. The oxides are obtained by quatemization of triphenylphosphine and hydrolysis of the phosphonium salt, or by reaction of hthiodiphenylphosphide with an alkyl halide or sulfonate and oxidation of the resulting phosphine with hydrogen peroxide. The derived hthio species react with aldehydes or ketones to give p-hydroxy phosphine oxides, which ehminate on treatment with a base such as sodium hydride or potassium hydroxide to form the alkene. In common with the Homer-Wadsworth-Emmons reaction, the phosphorus by-product is water soluble and easily removed from the product. 

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