Nitrone cycloaddition Wittig reaction

Tufariello and Tegeler18 have described a high-yield synthesis of the quinoliz-idine (11) by cycloaddition of nitrone (9) and the a/3-unsaturated ester (10) and then reduction (Scheme 1). The ester (10) was prepared conveniently from but-3-en-l-ol by ozonolysis of the tetrahydropyranyl ether followed by a Wittig reaction on the resultant aldehyde. The quinolizidine (11) was converted into lupinine (12) by a conventional procedure. 

Dipolar cycloaddition of nitrone 917 to methylenecyclopropane 918 was marginally stereoselective, and gave a 1 1.2 mixture of isoxazolidine adducts 919 and 920 in 80% yield (599). Thermal rearrangement of the mixture afforded the separable ketones 921 (26%) and 922 (38%). Conversion of these into lasubines I and II, respectively, had been reported some years previously (600). The second route, also not very stereoselective, used a Wittig reaction between acetyl-methylenetriphenylphosphorane and A -protected piperidin-2-ol 923 to m e pelletierine (924), Mannich condensation of which with veratraldehyde gave a 1 2.8 ratio of the ketones 921 and 922 (60%) (601). 

The Wittig-Horner olefination of the aldehyde 28 provided alkenes 29 which were subjected to radical cyclization leading to benzofused tricyclic j6-lactams 30, obtained as single diastereomers (Scheme 8) [36]. A convenient, direct regio- and stereoselective route to optically pure unusually fused or bridged tricyclic /3-lactams has been developed by the use of intramolecular nitrone-alkene cycloaddition reactions. For example, the aldehyde 21 can be transformed into nitrone 31 which subsequently was used for a variety... 

Synthesis of o ,jS-Unsaturated Aldehydes. Vinyltrimethylsilane undergoes [3 + 2] cycloaddition reactions with the aldehyde-derived nitrone (7) to provide the corresponding (trimethylsi-lyl)isoxazolidine adduct (8) in 84% yield (eq 5). Treatment of (8) with aqueous HE furnishes the a,/S-unsaturated aldehyde (9) in 95% yield. This methodology is general for the homologation of aldehydes and serves as an alternative to the traditional Wittig-type aUcenations. 

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