Synthetic applications of chromium(VI) reagents in combination with chlorotrimethylsilane

The synthetic utility of chromium(VI) reagents together with chlorotrimethylsilane, as new oxidizing systems, is described. Pyridinium dichromate (PDC) in combination with chlorotrimethylsilane oxidizes tert-butyldimethylsilyl ethers in good to excellent yields. Trimethylsilyl chlorochromate, a new chromium(VI) reagent, also was found efficient for this oxidative-deprotection method. These reagents were applied to the oxidation of some N-(2-phenyl-2-hydroxyethyl)azetidin-2-ones as well as N-(2-phenyl-2-trialkylsiloxy)azetidin-2-ones into their corresponding carbonyl compounds, key intermediates for N-unsubstituted β-lactams. Oxidation of hydroquinones and protected trialkylsilyl hydroquinones was also described. Protection of hydroquinones by means of the tert-butyldimethylsilyl group was achieved by using the readily available tert-butyldimethylchlorosilane (TBDMCS) and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as base, which avoids the use of sophisticated and (or) sensitive reagents.