Alcohol tosylation

Tosylation of alcohols. A detailed study of the tosylation of a typical primary alcohol finds that the highest yield (98%) is obtained by use of a 1 1.5 2 ratio of alcohol/tosyl chloride/pyridine in chloroform and at a temperature of 0°. The reaction requires about 2.5 hours. Secondary alcohols under the same conditions react more slowly. The rate can be increased by use of a 1 2 3 ratio of alcohol/ tosyl chloride/pyridine without a significant effect on the yield (85-98%). 

After decarboxylation, enolization in the alternative mode would cause racemization. However, this reasoning does not explain why 199 was racemized. The racemic a-aminoketones were eventually resolved via their bromocamphorsulfonates. Optically pure (—)-indolizidin-l-one (196) was reduced with lithium aluminum hydride to the alcohol, tosylated, and again reduced to (+)-indolizidine [Eq. (28)]. Since indolizidine obtained from R-pipecolic acid [Eq. (29)] was levorotatory, it followed that the absolute configuration of the original ketone was S.254 The optical rotatory dispersion (ORD) curve of the S(-)-ketone showed a strong negative Cotton effect as predicted by the octant rule. 

A fruitful approach to obtain asymmetric polymer synthesis was proposed by Overberger (126) who suggested that propagation could be influenced and optically active polymers could be synthesized by using optically active gegen-ions. Schmidt and Schuerch (127) followed up this suggestion and used boron trifluoride in conjunction with asymmetric Lewis bases (1-a-methyl benzyl alcohol, tosyl L-valine, camphor) to polymerize certain cyclic olefins. However, in spite of careful work and various modifications in reaction conditions, no optical activity was obtained in the polymers in this first attempt to test this ingenious hypothesis. 

COOEt), which (via the corresponding alcohol tosylate) can be converted to sabinene (767). ... 

Few examples of carboaminations of normal double and triple bonds are known. Similarly to allylic alcohols, tosylated allylic amines with (cthoxy)ethene form 2-ethoxy-4-vinylpyrrolidines 2. The reaction, mediated by stoichiometric amounts of palladium(II) acetate, can be changed to catalytic if copper(II) acetate is added as reoxidant of palladium(O). Moderate stereoselectivity (d.r. 64 36) is reported, however, without further structural assignment. 

The A-benzoylmeroquinene alcohol tosylate (61) was used in a new synthesis of quinotoxine (6) (Scheme 5) (19). The most interesting... 

Reduction to the alcohol, tosylation and conversion to the C-22 iodo derivative provides the substrate for reaction with a-(dimethyl allyl) nickel bromide. This coupling reaction gives the desmosterol side chain directly [scheme (7)] ... 

General Discussion. The tosylation of alcohols is one of the most prevalent reactions in organic chemistry. Optimized conditions for this reaction include the use of a 1 1.5 2 ratio of alcohol/tosyl chloride/pytidine in chloroform (eq 1). This procedure avoids formation of unwanted pytidinium salts inherent to... 

Similarly, a two-step procedure employing treatment of a mixture of tosic acid and various amino acids with alcoholic tosyl chloride results in the isolation of the esters of the amino acids as their p-toluenesulfonate salts in excellent yield. The tosic acid used in the esterification is added to make the amino acids more soluble and to prevent A-tosylation (eq 21). ... 

TBDMSCi as Cl Source. During the TBDMS protection of a primary alcohol under the standard conditions (TBDMSCI, DIPEA, cat. DMAP), a primary alcohol tosylate was simultaneously partially converted into the corresponding chloride, with a 70% combined 3ueld (eq 47). ... 

Substitution reactions Involving organoalumlnlum compounds. 4. Synthesis of alkylcyclopropanes by alkylation of hoaoallyllc alcohol tosylates with trlalkylalanes, G.A. Tolstlkov, A. Yu. Splval, S. I. Lomakina and A.V. Klchln, Tzv. Akad. Kauk SSSR. Sar. Khlm.. 1985, 1109. 

The first real trial of asymmetric polymerization of unsaturated cyclic monomers was reported by Shuerch et al [195]. Cyclic olefins (4,5-dihydro-2-methylfuran, indene, 1-methyl cyclopentene and a-angelica lactone) were polymerized using complexes of BF3 with asymmetric Lewis bases like 1-a-methylbenzyl alcohol, tosyl-1-valine or camphor. 

In addition to the numerous examples of the McMurry couplings described above, the following examples illustrate the power of the transformation in the synthesis of a broad range of natural products and non-natural molecules. Of particular note in the following examples is the impressive functional group tolerance of the McMurry conditions. In general, alcohols, tosyl alcohols, alkyl ethers, silyl ethers, alkyl silanes, vinyl silanes, amines, sulfides, and alkenes are inert to McMurry conditions. Acteals, halides, alkynes, nitriles, and carboxylic acids are semi-compatible. 

Lithium triethylborohydride has been shown to be an excellent reagent for the rapid reduction of alcohol tosylates to alkanes, even in hindrred cases. A comparative study on cyclohexyl tosylate marked out this reagent or the 9-BBN derivative (45) as the reagents of choice, but LiEtsBH is more readily available. 

Several reducing agents have been utilized to remove tosylate esters of sugars and other polyols. In particular, lithium aluminum hydride and lithium triethylborohydride have been most extensively used [20-23]. When secondary alcohol tosylates are used, epoxide intermediates are frequently involved. Reduction is observed to occur through either C-0 or O-S bond cleavage [24]. In this chapter, we discuss our results from the reduction of 6-0-tosylates of D-glucal and D-galactal with lithium aluminum hydride in THF. 

Stereospeciflc Conversion of Alcohols to Azides. Reaction of an alcohol with DPPA, Triphenylphosphine, and Diethyl Azodi-carboxylate forms the corresponding azides in 60-90% yields. The stereospeciflc nature of this reaction permits the conversion of A -sterols such as 3p-cholestanol exclusively to the 3a-cholestanyl azide in 75% yield. This synthesis is clearly superior to the alcohol - tosylate -> azide route which is longer and also prone to competing elimination reactions. 

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