Tandem reactions initiated by the oxidative decarboxylation of 1-benzoyl-2(S)-tert-butyl-6(S)-carboxyperhydropyrimidin-4-one

Treatment of the title perhydropyrimidinone with diacetoxyiodobenzene and iodine followed by addition of allyltrimethylsilane and boron trifluoride etherate afforded 1-benzoyl-2(S)-tert-butyl-2,3-dihydro-4(H)-pyrimidin-4-one in 65–71% yield, via an efficient three-step radical decarboxylation-oxidation-β-elimination tandem reaction. In contrast, when addition of allyltrimethylsilane/BF3·OEt2 was suppressed, a remarkable five-step tandem process led to the formation of vinylic iodide, 1-benzoyl-2(S)-tert-butyl-5-iodo-2,3-dihydro-4(H)-pyrimidin-4-one as the main product.