A-Tosyl derivatives

Compared with the sulphinimines, the A -tosylsulphinimines are less readily reduced and, to obtain acceptable yields, it is necessary to use larger amounts of catalyst. This suggests that the A-tosyl derivatives may be hydrolysed to the sulphinimines prior to the electrophilic attack by the carbene. 

The formation of an A-tosyl derivative of a meso-ionic l,2-oxazol-4-imine (370) in solution is possible, but the product was not isolated. 

Benzenium ions (199 X = acyl) on treatment with p-TSA in toluene undergo intramolecular O-alkylation to give the oxazolines (201 X=acyl Scheme 18, path b), rather than ring expansion to the Iff-azepine as mentioned earlier for the A-tosyl derivative (Scheme 18, path a). However, these oxazolines are thermally labile and on heating at 180°C rearrange in high yields (84-93%) to 1-acyl-lff-azepines (200 X = ArCO or Ac) <81AG(E)699>. 

Enantiomerically pure pipecolic acid (6) is accessible essentially by two well-established synthetic routes (i) cyclization of l- or D-lysine by reaction with disodium nitrosyl-pentacyanoferrate(II) with preservation of configuration at C2 215 216 (ii) ring closure of A ,Ae-bis(A-nitroso-A-tosyl) derivatives of l- or D-lysine, again with retention of chirality at C2. 217 Stereoselective synthesis of pipecolic acid derivatives, substituted in position 4, is achieved using the aza-Diels-Alder reaction of imines with dienes 218-220 or via an ene-iminium cyclization. 221 222 ... 

A total synthesis of xylerithrin was also reported, starting from 4,5-dimethoxy-3,6-diphenyl-o-benzoquinone and a />tosyl derivative of phenylacetic methylester [99], via 2-oxo-3-(p-hydroxyphenyl)-4,7diphenyl-5,6-dihydroxybenzofuran. 

TTte A-tosyl derivative of verruculotoxin (294) was prepared by cyclization of the (S),(S)-enantiomer of amino acid 293 on the action of ethyl chloroformate in the presence of A-methylmorpholine (91TL1417). 2-tert-Butylperhydropyrido[l,2-a]pyrazin-3-one was prepared by reacting 2-(N-... 

The reactions of lithiated sulfoximines 143 with cyclic enones give mixtures of regio- and diastereoisomers. The regioselectivity is dependent on the nature of the A-substituent on sulfur.59,75,81 A-Tosyl derivatives give exclusively a-1,4-addition products (144), while this type of adduct is slightly favored in the case of A-phenyl derivatives. A-terf-Butyl-diphenylsilyl (TBDPS) derivatives, however, favor y-1,4-adducts (145). In all cases the adducts were formed as mixtures of diastereoisomers except in the case of the y-1,4-adducts 145 (n = 1, Ar = Tol, R = Ph) which were obtained in low yield as a single diastereoisomer.75... 

Asymmetric aldol reactions may also be controlled with high diasteroselectivity, but this time for the anti isomer, in reactions of A -tosyl derivatives of esters derived from 7 (eq 3). Diastereoselectivities of up to 99 1 were achieved in the illustrated titanium(IV)-mediated reaction, which has been employed for the synthesis of dipeptide isosteres for incorporation into pharmaceutical building blocks.The selectivity reverses... 

With optically active amino alcohols and aldehydes, a mixture of diastereomers generally results. For N—H oxazolidines, the ratio of isomers is about 2 1, and for N—Me or N—Pr analogues the ratio is about 9 1. For A-tosyl derivatives, however, diastereomerically pure 2,4-cw-oxazolidines are isolated <92H(33)28i>. Trans isomers (189) are obtained in ratios >10 1 from the zinc chloride or trimethylsilyl triflate-catalyzed reaction of 2-methoxy-oxazolidines with allyltrimethylsilane or... 

Although unstable compounds, 2-bromo- and 2-chloropyrrole (also using SO2CI2) can be prepared by direct halogenation of pyrrole with the A-halo-succinimides 2-bromopyrrole can be conveniently prepared using l,3-dibromo-4,4-dimethylhydantoin and can be stabilised by conversion into its N-t-butoxycarbonyl derivative. Formation of A-tosyl derivatives is also recommended for stabilising 2-bromopyrrole. 

Au, extraction of, 20 Aza-9-crown-3 macrocycles, table. 186 A-tosyl-derivative. 41. 180, 258 Aza-lO-crown-3 macrocycles. toWc, 186 Aza-12-crown-4 macrocycles, 184, 185, 187. 

Reactions of Azepines. The first A -unsubstituted l/f-azepine (43) has been prepared by the reduction of the A -tosyl derivative (42) it is stabilized by hydrogen-bonding to the adjacent carbonyl group. 

It is interesting to know that the stereoselectivity of the adduct using Corey s catalyst is opposite to that normally observed for oxaza-borolidines generated from A-tosyl derivative of (S)-valine or hexahydrophenyl alanine. 

When quinoline 1-oxide was treated with 2-amjnopyridine in the presence of tosyl chloride under phase-transfer conditions in alkaline medium Ai-(pyridin-2-yl) quinolin-2-amine was obtained in 80% yield (Scheme 52) [111]. Also 3- or 4-aminopyridines can be regarded as nucleophiles, and their use in the same reaction with quinoline 1-oxide has been shown to afford A-tosyl derivatives of the corresponding iV-arylquinolin-2-amines in 15 and 53% yields, respectively. It is worth noting that the reactions of quinoline 1-oxide with Ai-tosyl derivatives of 2-, 3-, or 4-aminopyridine gave the corresponding 2-(Ai-tosyl-Ai-arylamino)quinolines in considerably higher yields. 

The corresponding difluoroindolines 38 were mostly isolated in case of indoles with electron-withdrawing groups. It was mentioned, that 3-fluoroindoles 5 and 37a are quite unstable the much more stable A-tosyl derivatives 23 and 39 can be prepared by treatment of 5 and 37a with tosyl chloride under basic catalysis [15],... 

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