Oximes alkenic mesylates

Ozonolysis of alkene 446 in the presence of acetaldehyde afforded diketone 448 through the intermediacy of 447. Ring expansion through Beckmann rearrangement took place when bis-oxime 449 was mesylated and warmed in aqueous tetrahydrofuran (THF). The bis-lactam so formed gave piperidinediol 450 on reduction with lithium aluminium hydride, and this compound was transformed into ( )-sparteine by treatment with triphenylphosphine, CCI4, and triethylamine (Scheme 105) <20050BC1557>. 

In many of these cases, the nucleophile is a C=C double bond (usually an alkenic group and less frequently an aromatic group). Alkenic oxime mesylates enable intramolecular cyclization by an electrophihc addition of the double bond to the electrophilic intermediate. These reactions are terminated by a proton loss. 

The efficient activation of oxime sulfonates by organoaluminum reagents enables the intramolecular cyclization of alkenic oxime mesylates, which involves the electrophilic addition of the intermediate ni-trilium ion to the double bond. This results in the direct formation of a wide variety of structurally diverse carbocyclic and heterocyclic systems. Four distinct cyclization modes, i.e. endo(B)-endo, endo(B)-exo, exo(B)-endo and exo(B)-exo are possible, as shown in Scheme 4P The values in parentheses refer to the yields obtained using SnCU. 

The alkenic cyclizations described above are terminated by deprotonation, yielding unsaturated im-ines. The intermediate carbocations, however, may also be captured by carbon nucleophiles to afford saturated imines. For example, treatment of the oxime mesylate (47) with Me Al followed by reduction with DIB AH predominantly produces the methylated product (48 equation 31). ... 

Generation of Electrophilic Cations. Complexation of Et2AlCl to ketones and aldehydes activates the carbonyl group toward addition of a nucleophilic alkyl- or allylstannane or allylsilane. Et2AlCl has been used to initiate Beckmann rearrangements of oxime mesylates. The ring-expanded cation can be trapped intermolecularly by enol ethers and cyanide and in-tramolecularly by alkenes (eq 5). ... 

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