Tosylate deprotection

The following procedure is representative of a co-cyclisation of a bis-toluenesulfonamide with a bis-toluenesulfonate followed by tosyl deprotection with sulfuric acid. 

Synthesis of 2-Alkanones and 3-Alken-2-one. Monoalkylation of 4-phenylsulfonyl-2-butanone ethylene acetal 1 takes place at the position a to the phenylsulfonyl group on successive treatment with butyllithium and then with an alkyl halide (or tosylate). Deprotection of the acetal group and subsequent elimination of the benzenesulfinic acid moiety with a base transforms the monoalkylation product to the corresponding 3-alken-2-one (eq 1). A 2-alkanone is obtainable from the monoalkylation product by reductive desulfurization and subsequent acidic deprotection (eq 2) ... 

Synthesis of the title compound is representative of a number of syntheses of nonaromatic nitrogen heterocycles via Pd(Ill-catalyzed amination of olefins. These tosylated enamines are not readily available by standard synthetic methods, and show potential for further functionalization of the heterocycle. The saturated amine can be synthesized from the title compound by hydrogenation of the double bond followed by photolytic deprotection. ... 

The disaccharide derivatives 196 and 197 of N-tosyl-L-serine, of interest for the study of D-galactose-binding lectins, were prepared by Kaifu and Osawa148 from 194 and 195, respectively, by protection of 0-4 and -6 with a benzylidene group, condensation of the acetal with tetra-O-acetyl-a-D-galactopyranosyl bromide (110) under Koenigs-Knorr conditions, and deprotection. 

Cathodic deprotection of tosylates of chiral alcohols was achieved without racemization by cleavage of the O—SO2 bond [351]. Optically active quaternary arsonium [352, 353] and phosphonium salts [354] are cathodically cleaved to tertiary arsines and phosphines respectively, with retention of the configuration. The first enantiomer enriched chiral phosphines have been prepared this way. 

Tosylation of 1146 gave 1147, which was converted to the iodo derivative, whose reaction with the sodium salt of guanine, followed by acetylation to aid its purification and then deprotection, gave 1148 (86JMC1384). The hydroxymethyl groups on C-5 of barbituric acid were introduced starting with malonic ester and then reaction with urea (93MI12). 

Witulski and Alayrac reported the synthesis of clausine C (clauszoline-L) (101) by a rhodium-catalyzed alkyne cyclotrimerization of diyne 1014 and propiolic ester 635 (561). Analogous to the hyellazole (245) synthesis (see Scheme 5.75), the diyne precursor 1014 required for this key cyclotrimerization reaction was obtained starting from readily available 2-iodo-5-methoxyaniline. Using Wilkinson s catalyst, [RhClfPPhsls], crossed-alkyne cyclotrimerization of 1014 and 635 led to N-tosylclausine C (1015) in 78% yield in an isomeric ratio of 3.8 1. Finally, deprotection of the tosyl group with TBAF in refluxing TFIF afforded clausine C (clauszoline-L) (101) (561) (Scheme 5.147). 

In search of a convenient procedure for preparing diazo substrates for the cycloaddition to Cgg, Wudl introduced the base-induced decomposition of tosyl-hydrazones [116]. This procedure allows the in situ generation of the diazo compoimd without the requirement of its purification prior to addition to Cgg. Since they are rapidly trapped by the fullerene, even unstable diazo compounds can be successfully used in the 1,3-dipolar cycloaddition. In a one-pot reaction the tosyUiydrazone is converted into its anion with bases such as sodium methoxide or butylHfhium, which after decomposition readily adds to Cgg (at about 70 °C). This method was first proven to be successful with substrate 142. Some more reactions that indicate the versatility of this procedure are shown in Table 4.4. Reaction of 142 with CgQ under the previously described conditions and subsequent deprotection of the tert-butyl ester leads to [6,6]-phenyl-C5j-butyric acid (PCBA) that can easily be functionalized by esterification or amide-formation [116]. PCBA was used to obtain the already described binaphthyl-dimer (obtained from 149 by twofold addition) in a DCC-coupling reaction [122]. 

Asymmetric alkylation of (S)-6oc-2-fert-butyl-3-methylimidazolidin-4-one (20) with 2-fluoroallyl tosylate, followed by first mild acidic deprotection of the products 21, and then basic hydrolysis of the A/ -methylamides (22) gave (S)-2-amino-4-fluoropent-4-enoic acid [50]. Basic hydrolysis of 22 was accompanied by partial racemization, a problem which was subsequently overcome by a nitrosative deamidation procedure to form 18 (Scheme 5). 

Alkyl (or acyl) derivatives of the 6-amino-6-deoxy carbohydrates are examples of derivatives in which the hydrophilic and hydrophobic moieties are linked at other positions than C-1. Thus 6-amino-6-deoxy-D-galactose derivatives 34 were prepared from l,2 3,4-di-0-isopropylidene-6-0-tosyl-a-D-galacto-pyranose by the following reactions (1) substitution of the leaving group at C-6 by a phthaloyl function, (2) hydrazinolysis to afford a 6-amino-6-deoxy intermediate, (3) reaction of acyl or sulfonyl chlorides at the amino function, (4) deprotection of the acetal rings to afford the expected glycolipid 34 [56]. 

Blechert s synthesis of the piperidine alkaloid (—)-halosaline 411 by RRM is outlined in Scheme 79 " In the presence of 5mol% of catalyst B, the ring rearrangement of metathesis precursor 409 proceeded cleanly with formation of both heterocyclic rings in 410. / s7/a deprotection of the cyclic silyl ether in 410 followed by selective reduction and removal of the tosyl group led to 411. 

In 1988, an improved synthesis of orlistat (1) was reported by the Hoffmann-La Roche discovery chemistry. The scheme involved a pivotal P-lactone 14. In the approach, an aldol condensation of aldehyde 7 with the dianion generated from octanoic acid and two equivalents of LDA. After tosylic acid-facilitated lactonization and Jones oxidation, the resultant lactone 14/14 was hydrogenated to establish two additional chiral centers. A battery of somewhat tedious protections and deprotections transformed 15 to P-lactone 19 via the intermediacy of 16,17, and 18. Six additional steps then converted P-lactone 19 to orlistat (1). This route may provide better overall yield in comparison to the previous scheme. However, too many protections and deprotections render this approach less elegant and not very practical for large-scale process. 

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