Oxime sulfonates rearrangement

If the rearrangement of oxime sulfonates is induced by organoaluminum reagents,the intermediate (71) is captured by the nucleophile originally attached to the Al. By this means an oxime can be converted to an imine, an imino thioether (R—N—C—SR), or an imino nitrile (R—N—C—In the last case, the nucleophile comes from added trimethyl si lyl cyanide. The imine-producing reaction can also be accomplished with a Grignard reagent in benzene or toluene. ... 

Another synthetic route via the Beckmann rearrangement, which is promoted by organoaluminum reagent along with alkylation, involves a new stereoselective reduction of the imino group. The starting oxime sulfonate (228) was synthesized from cyclopentanone (226) in three steps Reaction of 226 with 1-undecene in the presence of silver oxide produced the a-undecylcyclopentanone (227) which on successive treatment with hydroxylamine and methanesulfonyl chlo-ride-triethylamine gave the mesylate (228). Treatment of the oxime mesylate... 

As oxime derivatives, oxime sulfonates can be used preferentially for the following reasons (1) they are readily available from oximes using p-toluenesulfonyl chloride or methanesulfonyl chloride in the presence of base in almost quantitative yield, (2) they are easy to handle because of their fine crystalline properties, (3) they are sufficiently reactive to initiate the rearrangement by organoaluminum reagents. 

Beckmann rearrangement.3 Reaction of oxime sulfonates with simple Grignard reagents in dry toluene at —78° results in imines, which can be reduced to a-alkylamincs or alkylated with allylic or propargylic Grignard reagents to furnish a,a-diulkylnmincs. 

Beckmann rearrangement-alkylation sequenceOxime sulfonates react with AIR, to form rearranged imines, which are reduced to amines by DIBAH (equation I). The reaction involves selective migration of the R group anti to the oxime sulfonate. 

The Neber rearrangement of oxime sulfonates has been considered to proceed via a nitrene pathway or an anion pathway. If the latter mechanism is operative, the use of a certain chiral base might result in the discrimination of two enantiotropic a-protons to furnish optically active a-amino ketones. Verification of this hypothesis was provided by realizing the asymmetric Neber rearrangement of simple oxime sulfonate 83,... 

One significant (and indeed the first) preparative pathway to this ring system is the Neber rearrangement of oxime sulfonates. Recently it has been shown that this process can be mildly influenced by the introduction of chiral auxiliaries. Thus, rearrangement of the tosyl oxime 186 (formed in situ from the oxime 185) in the presence of catalytic amounts of the chiral quaternary... 

Another significant preparative pathway to the 2i/-azirine system is the Neber rearrangement of oxime sulfonates. The presence of strong electron-withdrawing groups in the a-position to the oxime increases the acidity of those protons, and thus favors the cycloelimination reaction under mild conditions. The Neber reaction occurs either through an internal concerted nucleophilic displacement or via a vinyl nitrene (Scheme 213) <2001EJ02401>. 

Treatment of a wide variety of oxime sulfonates with several equivalents of alkyl-aluminum reagents in CH2CI2 resulted in formation of the imines, which were directly reduced with excess DIBAH to give the corresponding amines, as shown in Sch. 19. This organoaluminum-promoted Beckmann Rearrangement of oxime sulfonates has been successfully applied to the stereoselective synthesis of naturally occurring alkaloids, pumiliotoxin C, and solenopsin A and B, as illustrated in Sch. 20 [43]. 

Combination of silyl enol ethers with the organoaluminum-promoted Beckmann rearrangement of oxime sulfonates resulted in a novel reaction system that leads to the formation of enaminones [44]. Treatment of a mixture of anfr-2-methylcyclohexa-none oxime sulfonate (33) and 2-(trimethylsiloxy)-l-octene in dry CH2CI2 with Et2AlCl at -78 °C for 30 min, and at 20 °C for additional 1 h resulted in formation of the enaminone 34 in 90 % yield (Sch. 21). 

Dependent on the stereochemistry of the oxime sulfonate and the different groups R , R, in many cases only one preferred stereoisomer rearranges. In hydrochloric acid/acetic acid, isomerization gives rise to only one final product. ... 

Oxime sulfonates were rearranged in the presence of diisobutylaluminum methyl sulfide to produce methylthioimidates, e.g. (291 equation 155), and methylthiolactim ethers in good yields. The adducts formed in the reaction of Grignaid reagents with trimeAylsilylmethyl isothiocyanate can be alkylated to furnish the A(-trimethylsilylmethylthioimidates (292 equation 156). ... 

Scheme 11.24 Asymmetric Neber rearrangement of oxime sulfonate 90...

Beckmann rearrangement of l-alkoxycarbonylazetidin-3-one oxime sulfonates (245) under the influence of aluminum oxide, followed by removal of the ester function, has provided the first synthesis of 4-imidazolidinone (Equation (73)) <86H(24)25>. 

The CR NR group can be introduced into ammonia, amines, hydroxy compounds, carboxamides, and sulfonamides to form amidines, imido-esters, etc., via imidosulfonates, obtained by the Beckmann rearrangement of oxime sulfonates.—B Benzophenone oxime benzene sulfonate and aniline warmed in benzene, and, after the exothermic reaction has ceased, further refluxed for 15-30 min. —>- N,N -diphenylbenzamidine. Y 92.5%. (F. e. s. P. Oxley and W. F. Short, Soc. 1948,1514.)... 

Kinetic evidence for such a dynamic path bifurcation in the mechanism of the Beckmann rearrangement has also been presented for reactions of oxime sulfonates (43, R /R = H/Me). In addition to the rearrangement product (amide), these substrates can also fragment (to alcohols), with the bifurcation in the mechanism apparently occurring after the rate-determining transition state. 

The reactions of oxime sulfonates of l-substituted-phenyl-2-propanone derivatives give both rearrangement products (amides) and fragmentation products (alcohols) and... 

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