All reactions were carried out under an inert atmosphere of nitrogen in oven dried glassware with magnetic stirring. Unless otherwise stated, starting materials were used upon purchased. Compounds were visualized by UV light at 254 nm and by dipping the plates in an aqueous potassium permanganate solution followed by heating. Flash column chromatography was performed over silica gel (300-400 mesh). The substrates in Scheme 1 are mercially available; The substrates in Scheme 2 were prepared by the following methods.