Tosylate anion

According to a detailed mechanistic study, the first step is the abstraction of the relatively acidic hydrazone proton (93- 97). This is followed by hydride attack on the trigonal carbon of the C=N bond, mainly from the a-side at C-3, together with the concomitant loss of the tosylate anion (97 -> 98). Expulsion of nitrogen from the resulting intermediate (98) yields a fairly insoluble anion-metal complex (99) which upon decomposition with water provides the methylene derivative (100). 

A mechanism which is consistent with the various experimental results for olefin formation involves the initial abstraction of the hydrazone proton (103->106) In this case, however, expulsion of the tosylate anion is associated with the abstraction of a second hydrogen from C-16 instead of hydride attack on the C=N bond (compare 97 98 and 106 107). Ex-... 

We have also seen good leaving groups other than halide ion, e.g. tosylate anion (cf. p. 88),... 

C(l)-Tosylation of 57 with [hydroxy(phenyl)iodonium] tosylate resulted in the J-1-tosylate 62 which could be further transformed by Sn2 reactions. Tosylation was proposed to proceed via the addition product 61 which, after Sn2 displacement by the tosylate anion and inversion at C-l, furnished 62 (Scheme 6) <1999T1755>. 

Formation of allylic alcohols is favored by supporting electrolytes with tosylate anions. Scheme 7, [11], Under these conditions, only small amounts of ketone were produced. It has been suggested that the role of the tosylate is as a nucleophile that traps the carbocation. Elimination from this intermediate then leads to the allylic alcohol. This explanation is supported by isolation of the... 

A mechanism which is consistent with the various experimental results for olefin formation involves the initial abstraction of the hydrazone proton (103 - 106)82 In this case, however, expulsion of the tosylate anion is associated with the abstraction of a second hydrogen from C-16 instead of hydride attack on the C=N bond (compare 97 - 98 and 106 - 107). Expulsion of nitrogen from the resulting intermediate (107) yields an anion (108) which is most probably stabilized in the form of a metal complex and can be readily decomposed by water to give an olefin (109). This implies that 17-d1-androst-16-ene (104) can be prepared by using deuterium oxide as the sole deuterated reagent.82... 

The reduction of tosylhydrazones can also be performed with sodium borodeuteride in boiling methanol or dioxane, but the mechanism of this reaction (in boiling dioxane at least) is radically different from that of the lithium aluminum deuteride reductions.82 With sodium borohydride the first step is apparently hydride attack on the carbon atom of the C=N bond which is probably concerted with the elimination of the tosylate anion (110 - 111). Migration of the hydrogen from nitrogen to C-3 in (111) concerted with expulsion of nitrogen, provides the corresponding methylene derivative (100).82... 

Complexation constants for binding of mono- and di-negative oxoanions by the cryptands can be determined by pH-potentiometry. For the more weakly-binding mononegative systems, NMR shifts can provide complementary information. For these studies we use the large size-excluded tosylate anion as the supporting electrolyte and all log K values are thus relative to this notional standard [19],... 

An ester of an alcohol with para-toluenesulfonic acid. Like halide ions, the tosylate anion is an excellent leaving group, (p. 477)... 

Arylamines.1 A novel method for amination of organometallic reagents involves activation of an O-tosylhydroxylamine by attachment to an auxiliary group that can be recycled. Thus aryl Grignard or lithium reagents react with the O-tosylate oxime of tetraphenylcyclopentadienone (1) to form an imine (2) with elimination of the tosylate anion. The imine is then converted into an ary lamine and the original oxime by treatment with excess hydroxylamine in aqueous pyridine. 

Inspection of models shows that the departure of a 3 a-tosylate anion cannot derive assistance from rear attack by the sr-electrons with ring A in its stable chair conformation (12). The alternative conformation (13) which might permit homoallylic participation [34] is highly strained and cannot compete with elimination of the m is-axial 4j8 proton to give cholesta-3,5-diene (14), the major reaction product (see p. 252 for further discussion). 

AT-Acylated 0-tosylhydroxyproline derivatives (CXLVIII) are known to undergo intramolecular displacement of 0-tosylate anion by the carboxylate anion under mild conditions leading to iNT-acylated lactones of allohydroxy-proline (CXLIX) (Patchett and Witkop, 1957). 

It seems likely as a consequence that a carbanion may be formed under these experimental conditions at the carbon vicinal to the sulfone group. This anion then would be conveniently placed at a six-carbon-atom distance from the electrophilic carbonyl, thus providing an expedient base to form the C-C bond clearly required for the construction of the six-membered ring of II. However, ketones become tertiary alcohols upon attack by carbon nucleophiles. Consequently, one of the alpha C-C bonds next to this ketone must be broken in order to preserve the ketone of the final product. The electron reorganization that would follow is consistent with a concomitant extrusion of tosylate anion. This is illustrated by three-dimensional structures IV and V (see Scheme 11.1)... 

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