N-Tosyl group

It is interesting to note that although the first examples of template effects were observed in nitrogen macrocycles (see chapter 2) no template effect appears to operate in the synthesis of 72. Richman and Atkins note this in their original report . The authors replaced the sodium cation with tetramethylammonium cations and still obtained greater than 50% yield of tetra-N-tosyl-72. Shaw considered this problem and suggested that because of the bulky N-tosyl groups, .. . the loss of internal entropy on cyclization is small He offered this as an explanation for the apparent lack of a template effect in the cyclization. 

An electrochemical method for amination has been reported by Shono et al. Derivatives of malonic esters containing an N-tosyl group were cyclized in high... 

Tri-O-acetyl-a-D-xylopyranosyl bromide106 (138) and N-tosyl-L-serine methyl ester107 (139) were condensed in the presence of Drierite and silver oxide, and then the O-acetyl and methyl ester groups were removed by treatment with sodium hydroxide, and the N-tosyl group by means of sodium in liquid ammonia, to give 140. Synthesis of this compound has also been described by other workers108-110 and the a-D an-omer by Brendel and Davidson.108... 

The reaction of the oxazolidinone with styrene-dg led to the selective formation of (Z)-27. Thus, styrene adds to the terminal double bond from the more congested face syn to the N-tosyl group. 

A mixture of epoxides 483 obtained on oxidation of 482 with dimethyldioxirane, when exposed to ferric chloride provided, as the kinetically controlled product, the a-aldehyde 484, which without purification was reduced to the a-alcohol 485. The exclusive formation of 484 is believed to occur via the benzyl cation 486, generated by Lewis-acid opening of the oxirane ring, suffering a stereospecific kinetic 1,2-hydride shift The amino alcohol 487 obtained after sequential removal of O-benzyl and N-tosyl groups from 485, on treatment with triphenylphosphine and iodine in the presence of imidazole furnished the tetracyclic base 488, which was oxidised to the ketone 489. Trapping of the kinetically generated enolate of 489 as the silylether, followed by palladium diacetate oxidation yielded the enone 490. The derived... 

An example of the use of a metal hydride to cleave an N-tosyl group from an indole is taken from the last step in a synthesis of Hamacanthin B [Scheme 8.267],523... 

Reagent (1) can also be converted to an ethylene transfer reagent by condensation with benzonitrile, followed by reduction of the ketosulfoximine and dehydration (eq 6). The resulting 5-vinyl-Af-tosylsulfoxiinine reacts with stabilized anions to give cyclopropanes. The N-tosyl group in N-tosylsulfoximines can be cleaved reductively using Sodium Anthracenide. ... 

The reaction of alkyllithium reagents with acyclic and cyclic tosylhydrazones can lead to mixtures of elimination (route A) and addition (route B) products (Scheme 22). The predominant formation of the less-substituted alkene product in the former reaction (Shapiro Reaction) is a result of the strong preference for deprotonation syn to the N-tosyl group. Nucleophilic addition to the carbon-nitrogen tosyl-hydrazone double bond competes effectively wiA a-deprotonation (and alkene formation) if abstraction of the a-hydrogens is slow and excess organolithium reagent is employed. Nucleophilic substitution is consistent with an Su2 addition of alkyllithium followed by electrophilic capture of the resultant carbanion. 

This chiral diene ligand displays a clear superiority over chiral phosphorus ligands in both enantioselectivity and catalytic activity. A second generation catalytic system tvas later reported for the highly enantioselective addition to N nosyl imines, for which the product is more easily converted into the free amine than that bearing a N tosyl group [120]. The more effective chiral ligand 60 had to be used (Scheme 1.36). 

Kresze and coworkers have found about a three order of magnitude rate increase in imino ene reactions when an N-tosyl group is replaced with an N-perfluoroalkanesulfonyl moiety [87]. Thus, with the glyoxylate ester-derived imine and the one from chloral 255 as the enophiles, reactions with acyclic olefins are very rapid and occur at room temperature [Eq. (60)]. In these ene reactions one stereoisomeric homoallylic amine 256 was typically generated, although the stereochemistry was not elucidated. However, in one reported case a 1 1 mixture of diastereomers was obtained. Mechanistic studies based upon kinetic isotope effects seem to indicate that this reaction may in fact be a two-step process rather than a concerted one [87b]. 

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