Michael addition of alkoxides

The Michael addition of alkoxides to nitroalkenes gives generally a complex mixture of products due to the polymerization of nitroalkenes.16 The effect of cations of alkoxides has been examined carefully, and potassium- or sodium-alkoxides give pure p-nitro-ethers in 78-100% isolated yield (Eqs. 4.12 and 4.13).17 When lithium-alkoxides are employed, the yields are decreased to 20-40%. 

Hori, K., Higuchi, S., Kamimura, A. Theoretical and experimental study on the stereoselectivity of Michael addition of alkoxide anion to nitro olefin. J. Org. Chem. 1990, 55, 5900-5905. 

The intramolecular Michael addition of alkoxide anions to a, /S-unsaturated esters is often seen in the preparation of tetrahydropyrans (Scheme 2). Usually, 2,6-cis-disubstituted tetrahydropyrans are obtained with high stereoselectivity via the 6-membered transition state model 1. In the total syntheses... 

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