1,8-Diazabicyclo[5.4.0]undec-7-ene-Promoted Oxidation by Atmospheric Oxygen of an Allylsilane Derived from γ-Formyl-Substituted Cyclopentene

(1 R ,4 R ,5 S -5-{[( tert -Butyldimethylsilyl)oxy]methyl}-4-(trimethylsilyl)cyclopent-2-ene-1-carbaldehyde in a toluene–DBU–O 2 medium undergoes a tandem-type isomerization/oxidation transformation to form (3 S ,4 S ,5 S )-5-{[( tert -butyldimethylsilyl)oxy]methyl}-3-hydroxy-4-(trimethylsilyl)cyclopent-1-ene-1-carbaldehyde in a good yield. Possible way of formation of the product was proposed, involving the C 3 -oxidation of the starting allylsilane by a carbanion/enolate mechanism.