Oxidopyridinium ions bearing an ester group at the 5-position undergo (4 + 3) cycloaddition reaction to afford congeners of 7-azabicyclo[4.3.1]­decane. The reaction generally proceeds in high yield, although an excess of diene is often required to achieve such yields. The reaction is highly regioselective, but not endo/exo selective. It appears the cycloaddition process can be either kinetically or thermodynamically controlled, depending on the nature of the diene used and the reaction time. An intramolecular Heck reaction was used to demonstrate that some chemistry is possible with the cycloadducts.

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The ABCE tetracyclic ring system of daphnicyclidin A was prepared using an intramolecular (4+3) cycloaddition of an oxidopyridinium ion as the key step. This route consists of a 10-step synthesis...

Primary alcohols are converted into dialkyl disulfides via heating in situ generated O-alkyl S-difluoro(ethoxycarbonyl)methyl xanthates from ethyl bromodifluoroacetate and potassium xanthates, prepared from primary alcohols and carbon disulfide in the presence of KOH. The reaction mechanism is suggested as an alkyl C[1,3] shift followed by a radical mechanism. This extends to the Chugaev elimination which yields olefins. The current research provides easy access to dialkyl disulfides from commercially available primary alkanols.

N-alkylation of 5-hydroxynicotinic acid esters with electrophiles containing diene functionality produces salts that undergo intramolecular (4 + 3) cycloaddition reactions upon heating in the presence of base. Initial studies used a three-carbon tether to join the pyridinium ion and diene, revealing some aspects of the inherent selectivity of the reaction with such substrates. Much more challenging was the synthesis of related species possessing only a two-carbon tether. Nevertheless, the cycloaddition of such compounds was successful, leading directly to the ABC ring system of the alkaloid daphnicyclidin A.