Stereocontrol of 1,5-related stereocentres using an intermediate silyl group--the diastereoselectivity of nucleophilic attack on a double bond adjacent to a stereogenic centre carrying a silyl group.

摘要: R-5-Methylcyclohex-2-enone 1 reacts successively with the phenyldimethylsilylzincate reagent and acetaldehyde to give regiocontrol aldols 7, dehydration of which creates E-exocyclic double bond α,β-unsaturated ketone 2. Conjugate addition ethylcuprate this compound takes place high (96 ∶ 4) selectivity in favour R stereoisomer 12, hydrolysis gives (2R,3R,5S,2′R)-2-(but-2′-yl)-3-dimethyl(phenyl)silyl-5-methylcyclohexanone 3. The oxime acetate undergoes fragmentation presence trimethylsilyl trifluoromethanesulfonate 3R,7R,5E-3,7-dimethylnon-5-enonitrile 4, an open-chain 1,5-stereochemical relationship is set up a level stereocontrol. A similar sequence adding 4-methylpentylcuprate enone 2, 3R,7R,5E-3,7,11-trimethyldodec-5-enonitrile 20. Reduction hydrogenation nitrile 3R,7R-3,7,11-trimethyldodecanal 22, can be converted into phytol 25. ketoaldehyde 29 samarium iodide only alcohol 30, radical anion has attacked from top surface, just like cuprate reagents their reactions