Sulfoxides alcohol synthesis

C ( propyl) N phenylmtrone to N phenylmaleimide, 46, 96 semicarbazide hydrochloride to ami noacetone hydiochlonde, 46,1 tetraphenylcyclopentadienone to diphenyl acetylene, 46, 44 Alcohols, synthesis of equatorial, 47, 19 Aldehydes, aromatic, synthesis of, 47, 1 /3-chloro a,0 unsaturated, from ke tones and dimethylformamide-phosphorus oxy chloride, 46, 20 from alky 1 halides, 47, 97 from oxidation of alcohols with dimethyl sulfoxide, dicyclohexyl carbodumide, and pyndimum tnfluoroacetate, 47, 27 Alkylation, of 2 carbomethoxycyclo pentanone with benzyl chloride 45,7... 

Ogawa, S. Furukawa, N. Regiospecific ortho lithiation of o-halophenyl p-tolyl sulfoxides and synthesis of met -substituted optically active aryl alcohols./. Org. Chem. 1991, 56, 5723-5726. 

A three-stage synthesis of allylic alcohols has been devised (Scheme 32)," which consists of (i) alkylation of a sulfone-stabilized allylic carbanion (ii) peroxy acid oxidation of the allylic sulfone to give a 2,3-epoxy sulfone and (iii) reductive elimination of the 2,3-epoxy sulfone to give the allylic alcohol. The overall strategy is similar to that of the Evans-Mislow allylic alcohol synthesis based on the 2,3-sig-matropic rearrangement of allylic sulfoxides. However, there are regiochemical advantages to the sul-... 

Allylic sulfoxides are known to equilibrate with their isomeric sulfenates via a 2,3-sigmatropic shift, which has been developed into a useful allylic alcohol synthesis when the unstable sulfenate is trapped (Scheme 14). However, this rearrangement is reversible and so need not necessarily interfere with pyrolytic elimination of the sulfoxide, e.g. the long-chain hydroxydiene (69) was obtained on pyrolysis of the sulfoxide (68 equation 32). A study of substitution effects on the relative rates of rearrangement... 

Benedict, D. R., Bianchi, T. A., Cate, L. A. Synthesis of simple unsymmetrical ethers from alcohols and alkyl halides or sulfates the potassium hydroxide/dimethyl sulfoxide system. Synthesis 1979,428-429. 

The dihydrothiazine oxide (73) gives the (Z)-allylic sulfoxide (77), which (/,/2 = 90 min) is slowly converted to a mixture of ( )-allylic sulfoxides (78) that are epimeric at the sulfur atom. This well-precedented transformation of (77) to the thermodynamically more stable (78) involves conformational inversion of the sulfenate ester (79a) to (79b). At any stage of this equilibrium, treatment with a thiophile such as trimethyl phosphite can stereospecifically lead to the (F -hydroxy carbamate (74) (Scheme 13) <84JA7861>. This versatile transformation has been applied to stereospecific vicinal amino alcohol synthesis. 

The first task was to prepare the chiral sulfoxide. The synthesis began with the conversion of methyl propionate (144) to keto-sulfide 145. Enzymatic reduction of the ketone using Baker s Yeast gave 146 with decent enantiose-lectivity. A directed oxidation of the sulfide provided an unequal mixture of sulfoxides 147 and 148 (and presumably minor amounts of material derived from the 4-5% of ent- 46 present in the starting material) from which 148 could be isolated in 50% yield. Dehydration of the alcohol provided 149 (along with some of the Z isomer). Notice that Mori decided to place the alcohol beta to the sulfoxide in the precursor of 149. There might be a number of reasons for this, but one is that it facilitated the elimination reaction (dehydration) because of the electron-withdrawing properties of the sulfoxide. 

The formation of the above anions ("enolate type) depend on equilibria between the carbon compounds, the base, and the solvent. To ensure a substantial concentration of the anionic synthons in solution the pA" of both the conjugated acid of the base and of the solvent must be higher than the pAT -value of the carbon compound. Alkali hydroxides in water (p/T, 16), alkoxides in the corresponding alcohols (pAT, 20), sodium amide in liquid ammonia (pATj 35), dimsyl sodium in dimethyl sulfoxide (pAT, = 35), sodium hydride, lithium amides, or lithium alkyls in ether or hydrocarbon solvents (pAT, > 40) are common combinations used in synthesis. Sometimes the bases (e.g. methoxides, amides, lithium alkyls) react as nucleophiles, in other words they do not abstract a proton, but their anion undergoes addition and substitution reactions with the carbon compound. If such is the case, sterically hindered bases are employed. A few examples are given below (H.O. House, 1972 I. Kuwajima, 1976). 

Solvent for Displacement Reactions. As the most polar of the common aprotic solvents, DMSO is a favored solvent for displacement reactions because of its high dielectric constant and because anions are less solvated in it (87). Rates for these reactions are sometimes a thousand times faster in DMSO than in alcohols. Suitable nucleophiles include acetyUde ion, alkoxide ion, hydroxide ion, azide ion, carbanions, carboxylate ions, cyanide ion, hahde ions, mercaptide ions, phenoxide ions, nitrite ions, and thiocyanate ions (31). Rates of displacement by amides or amines are also greater in DMSO than in alcohol or aqueous solutions. Dimethyl sulfoxide is used as the reaction solvent in the manufacture of high performance, polyaryl ether polymers by reaction of bis(4,4 -chlorophenyl) sulfone with the disodium salts of dihydroxyphenols, eg, bisphenol A or 4,4 -sulfonylbisphenol (88). These and related reactions are made more economical by efficient recycling of DMSO (89). Nucleophilic displacement of activated aromatic nitro groups with aryloxy anion in DMSO is a versatile and useful reaction for the synthesis of aromatic ethers and polyethers (90). 

Notable examples of general synthetic procedures in Volume 47 include the synthesis of aromatic aldehydes (from dichloro-methyl methyl ether), aliphatic aldehydes (from alkyl halides and trimethylamine oxide and by oxidation of alcohols using dimethyl sulfoxide, dicyclohexylcarbodiimide, and pyridinum trifluoro-acetate the latter method is particularly useful since the conditions are so mild), carbethoxycycloalkanones (from sodium hydride, diethyl carbonate, and the cycloalkanone), m-dialkylbenzenes (from the />-isomer by isomerization with hydrogen fluoride and boron trifluoride), and the deamination of amines (by conversion to the nitrosoamide and thermolysis to the ester). Other general methods are represented by the synthesis of 1 J-difluoroolefins (from sodium chlorodifluoroacetate, triphenyl phosphine, and an aldehyde or ketone), the nitration of aromatic rings (with ni-tronium tetrafluoroborate), the reductive methylation of aromatic nitro compounds (with formaldehyde and hydrogen), the synthesis of dialkyl ketones (from carboxylic acids and iron powder), and the preparation of 1-substituted cyclopropanols (from the condensation of a 1,3-dichloro-2-propanol derivative and ethyl-... 

One of the first uses of the allylic sulfoxide-sulfenate interconversion was made by Jones and coworkers64, who reported exclusive suprafacial rearrangement of the allyl group in the steroidal sulfoxide 17 shown in equation 13. Two other examples are shown in equations 1465 and 1566. Evans and coworkers have demonstrated the utility of the suprafacial allylic sulfoxide-sulfenate rearrangement in a new synthesis of the tetracyclic alcohol 24 (equation 16)67, as well as in a synthesis of prostaglandin intermediates as shown in equation 1768. The stereospecific rearrangement of the unstable sulfenate intermediate obtained from the cis diol 25 indicates the suprafacial nature of this process. 

In addition to the synthetic applications related to the stereoselective or stereospecific syntheses of various systems, especially natural products, described in the previous subsection, a number of general synthetic uses of the reversible [2,3]-sigmatropic rearrangement of allylic sulfoxides are presented below. Several investigators110-113 have employed the allylic sulfenate-to-sulfoxide equilibrium in combination with the syn elimination of the latter as a method for the synthesis of conjugated dienes. For example, Reich and coworkers110,111 have reported a detailed study on the conversion of allylic alcohols to 1,3-dienes by sequential sulfenate sulfoxide rearrangement and syn elimination of the sulfoxide. This method of mild and efficient 1,4-dehydration of allylic alcohols has also been shown to proceed with overall cis stereochemistry in cyclic systems, as illustrated by equation 25. The reaction of trans-46 proceeds almost instantaneously at room temperature, while that of the cis-alcohol is much slower. This method has been subsequently applied for the synthesis of several natural products, such as the stereoselective transformation of the allylic alcohol 48 into the sex pheromone of the Red Bollworm Moth (49)112 and the conversion of isocodeine (50) into 6-demethoxythebaine (51)113. 

Mikolajczyk and coworkers have summarized other methods which lead to the desired sulfmate esters These are asymmetric oxidation of sulfenamides, kinetic resolution of racemic sulfmates in transesterification with chiral alcohols, kinetic resolution of racemic sulfinates upon treatment with chiral Grignard reagents, optical resolution via cyclodextrin complexes, and esterification of sulfinyl chlorides with chiral alcohols in the presence of optically active amines. None of these methods is very satisfactory since the esters produced are of low enantiomeric purity. However, the reaction of dialkyl sulfites (33) with t-butylmagnesium chloride in the presence of quinine gave the corresponding methyl, ethyl, n-propyl, isopropyl and n-butyl 2,2-dimethylpropane-l-yl sulfinates (34) of 43 to 73% enantiomeric purity in 50 to 84% yield. This made available sulfinate esters for the synthesis of t-butyl sulfoxides (35). 

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