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Reaction of silyl enol ethers (1a–f) with N-chlorosuccinimide afforded siloxycarbinyl cations which were trapped by nucleophiles (NaN3 and MeOH); subsequent rearrangement of the azido products (2a,b,d,e–N3) under reflux in decalin led to anilide derivatives (3a,b,d,e).

The kinetics of the reactions of 3,3,10,10-tetramethyldispiro[5.0.5.1]trideca-1,5,8,12-tetraone (7) with a series of substituted pyridines were investigated. The compound underwent well behaved second-order reactions with nucleophiles to afford the polar zwitterionic products (9). Values of log k in acetonitrile fall on a straight line when plotted against the pKa values of a series of 3- or 4-substituted pyridines and exhibit a Bronsted slope of 0.24. Methyl substitution in the neighbourhood of the reaction centre in the substrate or a nucleophile produced a fall in reactivity to some degree (1/2–1/10). These results together with an unusual solvent effect are interpreted by a preassociative mechanism in which a polar encounter complex is formed prior to the cyclopropane ring opening to give the final product (9).

The kinetics of the reaction of 3,3,10,10-tetramethyldispiro[5.0.5.1]tridecane-1,5,8,12-tetraone (1) with pyridine was studied in various pure solvents (protic and aprotic). Although this reaction afforded a polar zwitterion [the pyridinium β-oxoenolate derivative (2)], the solvent effect on the reaction rate was not as remarkable as that in the Menschutkin reaction; it was related to Gutmann's DN parameters rather than to the Dimroth–Reichardt ET values. The multiparameter analysis approach according to the Krygowski–Fawcett model in aprotic solvents and the Taft–Kamlet model in protic solvents was successful, giving log k2=–8.82 × 10–3ET– 17.4 × 10–3DN– 3.36 (r= 0.927; n= 8) and log k2=–0.734α+ 0.162β– 3.15 (r= 0.941; n= 6), respectively, Mechanisms are discussed.

1,4-Dienes were prepared by the homo-1,4-elimination of αα′-dihydroxy derivatives of cyclopropanes with diphosphorus tetraiodide in the presence of pyridine.

The title compounds (1, 3) were prepared by photochemical isomerisation of 2,3-dihydrofurans (2, 4) and reacted with pyridines or pyrazine to give zwitterionic products (5) which are thought to be intramolecular charge-transfer complexes.