High π-facial stereodifferentiation is obtained on Lewis-acid-promoted Diels-Alder additions to both neopentylether-shielded acrylates (95.6 to 99.3% d.e.) and 2,3-butadienoic acid ester (99% d.e.) as used for the enantioselective synthesis of (-)-β-santalene. Similar shielding governs the 1,4-addition of nBu₃P- or cyanide-stabilized MeCu·BF₃ to chiral trans-enoates generating β-substituted carboxylic acids e.g. (S)-citronellic acid in 80 to 98% overall enantioselectivity. Intramolecular magnesium-ene reactions are studied and applied to the syntheses of (±)-Δ9(12)-capnellene, sinularene, 12-acetoxysinularene and khusimone. Aprotic 1,4-addition of the lithium enolate of α-methyldiphenylsilylacetate to cyclopentenone serves for a direct synthesis of methyl jasmo nate. A novel double-π-face-selective Michael addition of a neopentylether-shielded senecioate-lithium-dienolate to cyclopentenone serves for the enantioselective synthesis of (-)-khusimone.