Hydroxyl groups dimethyl sulfoxide

The use of dimethyl sulfoxide-acetic anhydride as a reagent for the oxidation of unhindered steroidal alcohols does not appear to be as promising due to extensive formation of by-products. However, the reagent is sufficiently reactive to oxidize the hindered 11 j -hydroxyl group to the 11-ketone in moderate yield. The use of sulfur trioxide-pyridine complex in dimethyl sulfoxide has also been reported. The results parallel those using DCC-DMSO but reaction times are much shorter and the work-up is more facile since the separation of dicyclohexylurea is not necessary. Allylic alcohols can be oxidized by this procedure without significant side reactions. 

The electronic effects of many substituents have been examined by studies of PMR118,119 sulfinyl and sulfonyl groups have been included in some of these. For example, Socrates120 measured the hydroxyl chemical shifts for 55 substituted phenols in carbon tetrachloride and in dimethyl sulfoxide at infinite dilution, and endeavored to... 

The present procedure affords a simple and general method for preparing bromohydrins from alkenes which avoids the heterogeneous solvent systems often used in such reactions. Labeling experiments have demonstrated that the oxygen from the dimethyl sulfoxide appears in the hydroxyl group of the bromohy-drin. Therefore the role of the water is to hydrolyze the intermediate /3-bromodimethylsulfoxonium ion. 

Quebrachitol was converted into iL-c/j/roinositol (105). Exhaustive O-isopropylidenation of 105 with 2,2-dimethoxypropane, selective removal of the 3,4-0-protective group, and preferential 3-0-benzylation gave compound 106. Oxidation of 106 with dimethyl sulfoxide-oxalyl chloride provided the inosose 107. Wittig reaction of 107 with methyl(triphenyl)phos-phonium bromide and butyllithium, and subsequent hydroboration and oxidation furnished compound 108. A series of reactions, namely, protection of the primary hydroxyl group, 0-debenzylation, formation of A-methyl dithiocarbonate, deoxygenation with tributyltin hydride, and removal of the protective groups, converted 108 into 7. 

The diphenolic protoberberine methobromide 285 derived from 283 was refluxed in aqueous ethanolic sodium hydroxide for 12 hr to furnish the quinomethide 287 in 92% yield (Scheme 50). Compound 287 was treated with dimethyl sulfoxide to give rise to the desired diphenolic ochotensimine analog 288 through enolization (150,151). The presence of the phenolic hydroxyl group is essential in this rearrangement because the benzyl ether (284) was recovered unchanged under the same alkaline conditions. 

Useful syntheses of D- and L-lyxose from 1,3-O-benzylidene-D- and L-arabinitol have been achieved through the highly selective oxidation of the primary hydroxyl groups by dimethyl sulfoxide-dicyclohexylcarbodiimide.463 Oxidation of but one of the two (equivalent) hydroxyl groups in 1,3,4,6-tetra-O-benzyl-D-mannitol464 and l,6-di-0-benzyl-2,5-0-methylene-D-mannitol465 was possible with dimethyl sulfoxide-acetic anhydride. 

The silylation reactions were performed by treatment of a solution of the substrate (1 mol. equiv.) in oxolane [or a A 1 (v/v) mixture of oxolane—dimethyl sulfoxide for substrates insoluble in oxolane] with (l.A—1.5 mol. equiv.) and trlphenylphosphine (0.5 mol. equiv.). The structures of the substrates employed and of the products obtained, and yields, are shown in Figure 1. Under the particular reaction conditions employed secondary hydroxyl groups are either not silylated or are silylated distinctly slower. 

Confirmation of these results was provided by a different laboratory67 in studies with allyl a-L-fucopyranoside. Partial benzylation of this compound, under conditions similar to those described previously,66 also gave the 2,4- and 3,4-dibenzyl ethers in the ratio of 3 2. In both publications, the structures assigned were primarily confirmed by methylation of unreacted hydroxyl groups with methyl iodide-sodium hydride in dimethyl sulfoxide,68 followed by catalytic debenzylation, and isolation and characterization of the known methyl ethers. 

The key role of C6 in stabilizing the native cellulose lattice is supported by recent findings concerning the mechanism of action of the dimethyl-sulfoxide-paraformaldehyde solvent system, which is quite effective in solubilizing even the most crystalline of celluloses. The crucial step in the mechanism proposed for the action of this system is substitution of a methylol group on the primary hydroxyl at the C6 carbon (26, 27). 

The quaternary salt 366 was not obtained from 9-hydroxyl-2-methyl-4 -pyrido[ 1,2-a]pyrimidin-4-one 365 and benzyl chloride by heating in nitromethane (92KGS1660). The hydroxy group of 9-hydroxylpyridopy-rimidin-4-one 365 was alkylated with methyl iodide in dimethyl sulfoxide at 40°C for 30 hours to give 9-methoxy derivative 367 in 9% yield. 

Monomolar benzylation of methyl 2,3-di-0-benzyl-a-D-galactopyranoside in DMF gave 2,3,6-tri-O-benzyl derivative in 73% yield [52], The primary 6-benzyl ether also forms the major part of the monobenzyl fraction obtained from methyl a-D-galactopyranoside or from its p-anomer [53]. Interestingly, position 6 becomes less reactive than position 2 if 3,4-0-isopropylidene acetals is used to protect the other two secondary hydroxyl groups. The ratio of 2- and 6-benzyl ethers was found to be 11 1 in the a-anomer and 2.5 1 in the p-anomer [53] (see also, Ref. [54]). Uridine [55], cyti-dine [56], and 4-(methylthio)uridine [56] also prefer OH-2 over the primary position when benzylated in dimethyl sulfoxide (for other benzylations in this solvent, see Refs. [35, 57]). 

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