Synthesis of (±)-epi-Stegobinone Utilizing Silacyclopropanes as Synthetic Intermediates

2,3-Dihydro-4H-pyran-4-ones and 2,3-dihydro-4-pyridinones by cyclizations of alpha,beta-unsaturated 1,3-diketones

A variety of alpha,beta-unsaturated 1,3-diketones cyclize to 2,3-dihydro-4H-pyran-4-ones in an acidic aqueous medium, with exceptions being alpha,beta-unsaturated 1,3-diketones in which the beta carbon is substituted by a phenyl group. Addition of 1-butanamine to the reaction medium results in the formation of 2,3-dihydro-4-pyridinones, which appear to arise via an initial 1,4-addition of the amine to the alpha,beta-unsaturated 1,3-diketones.