Potassium /-butoxide in DMSO

Sulfoxides containing P-hydiogen atoms, eg, di-Abutylsulfoxide [2211 -92-9] react with strongly basic systems, eg, potassium /-butoxide, in DMSO by sulfenic acid elimination to produce olefins (eq.l2) (44) ... 

The method of choice for the preparation of cholesta-3,5-diene is treatment of cholesteryl tosylate with potassium /-butoxide in DMSO. The mesylate and chloride react similarly. 

Acetoxyandrost-5-en-l 7-one (59) is converted into the ethylene ketal (60) by treatment with ethylene glycol, triethylorthoformate and p-toluenesulfonic acid. The ketal is brominated with pyridinium bromide perbromide in THF and then treated with sodium iodide to remove bromine from the 5 and 6 positions. This gives the 16a-bromo compound (61) which is hydrolyzed in methanol to the free alcohol (62). Dehydrobromination is effected with potassium /-butoxide in DMSO to give the A15-compound (63). Add catalyzed hydrolysis of the ketal in aqueous acetone gives the title compound... 

The reduction of 2-phenylisatogen by potassium /-butoxide in DMSO or polarography gave the radical 213, and related compounds gave similar radicals (73T2425). 

Preparation. The original procedure (1, 315-318) for the preparation employed reaction of trimethyloxosulfonium iodide with NaH in DMSO. A newer, less hazardous route involves reaction of trimethylsulfoxonium iodide (Aldrich) with potassium /-butoxide in DMSO at room temperature.1... 

The mixture of cyclopropanes stereoisomeric at the cyclopropane group to 46 reacts with potassium /-butoxide in DMSO to give 47-49101. 

Oxindoles substituted in unusual positions have been obtained by base-induced intramolecular nucleophilic substitution of hydrogen in OT-nitroacylanilides. For example, treatment of the substrate 228 with potassium /-butoxide in DMSO gave the product 229 (Equation 71). However, the yields in such annulations are generally low, and some substrates give mixtures of isomeric oxindoles <2002S2203>. 

Dehydrochlonnation. The dehydrochlorination of the sterically hindered meso-3,4-dichloro-2,2,5,5-tetramethylhexane (1) by potassium /-butoxide in DMSO proceeds normally by anti-coplanar elimination to give the less stable (E)-olefin 2 as the major product. However, syn-elimination to the (Z)-isomer 3 becomes the main reaction in THF or r-butyl alcohol. The difference may be related to the differing aggregates of the base in the various solvents. ... 

The first synthesis of d4T was accomplished in 1966 by Horwitz from l-(2-deoxy-3,5-epoxy-/3-D-r/2reo-pentosyl)thymine abstraction of a proton from the 2 -position by potassium butoxide in DMSO resulted in an opening of the oxetane ring and formation of d4T. Other syntheses were based on the elimination of sulfoxide or the selenoxide moiety placed at the C-2 position in the nucleoside, which was prepared from cheap lactone 6 (O Scheme 7) [6]. 

Framen s procedure. A solution of potassium /-butoxide in DMSO is added by drops to a solution of trimethylsulfonium bromide or perchlorate in DMSO at room temperature. Sodium methoxide and sodium ethoxldc serve also as the base, and DMF is satisfactory as solvent. Reagent generated by this method converts mono-functional aldehydes and ketones into epoxides in good yield. I ranzcn initially... 

Another 8-elimination to give an olefin observed by Schriesheim et al. is the base-catalyzed decomposition of aliphatic sulfoxides and sulfones. With potassium ( butoxide in DMSO the reaction proceeds easily at 55° ... 

Dehydrohalogenation [1, 916-917, after citation of ref. 34]. l,2-Dichloro-2,2-dimethyl-3-propylcyclopropane (1) on treatment with the potassium /-butoxide in DMSO at 30° is converted into 2,2-dimethylallylidenecyclopropane (2).34a... 

The reaction of l,l-dichloro-2,2,3-trimethylcyclopropane (14) with potassium /-butoxide in DMSO (inverse addition at 25°) results in two major products, 2-chloro-3,3-dimethylmethylenecyclopropane (16) and 2-mcthylpentene-l-yne-3 (17)36c... 

Cleavage of methyl esters.1 The reagent (in HMPT) is very effective for cleavage of methyl esters under mild conditions. Thus the very hindered methyl mesitoate is cleaved to the acid in quantitative yield at 25° (1.25 hours). Methyl O-methylpodocarpate (1) is readily cleaved to O-methylpodocarpic acid in quantitative yield at 25° (1.5 hours). This reaction had been effected previously with potassium /-butoxide in DMSO, but required 2 hours at 52°.2 Bartlett and Johnson also examined the selective ester cleavage of methyl 3/3-acetoxy-A5-etienate (2). 

Isomerization of unsaturated compounds (1, 913-914 2, 336). 1-Methylcyclo-prnpene is isomerized to methylenecyclopropane in quantitative yield by treatment with a catalytic amount of potassium /-butoxide in DMSO for 2 hours at room temperature.3... 

Di- and trisubstituted epoxides. j3-Hydroxyselenides (1), prepared by the method illustrated above, can be converted into epoxides. Alkylation with methyl iodide in the presence of silver tetrafluoroborate gives the resulting salts (2), which are treated with potassium -butoxide in DMSO. An epoxide (3) and methyl phenyl selenide are formed by way of the betaine (a). Unfortunately, when two alkyl groups are attached to the carbon bearing the SeCeHs group. 

Chlorobenzocyclopropeme. Treatment of (1), 3,4,7,7-tetrachlorobicyclo-[4.1.0]heptane, with potassium /-butoxide in DMSO (1 hour, 20°) gives 2-chlorobenzocyclopropene (2) in about 50% yield. The original paper should be consulted for a possible mechanism. ... 

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