We have previously reported on the phosphine-mediated cycloisomerization of alkynyl hemiketals to cyclic keto enol ethers. When the alkyne is singly substituted (terminal alkyne) the keto enol ether rapidly dimerizes via [4+2] cycloaddition. Monomeric cyclic keto enol ethers are the product when internal alkynes are used. Here we report on reactions that make use of the latent functionality present in cyclic keto enol ethers. Reactions that move one step beyond this product arise via new reactions. In one case, introducing ethyl 2,3-butadieneoate in the presence of triphenylphosphine gives a new spirocyclic product. If DABCO is used in place of triphenylphosphine, a tetrahydropyran-fused dihydro-oxepine species is the product. Details of the reaction, their scope, and potential applications will be presented.

One step beyond: Diversifying cycloisomerization products through new reactions

253rd National Meeting (2017)

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