Simple and Condensed β-Lactams. Part 34. Oxidative Cyclization by Lead(IV) Acetate of 1-(4-Methoxyphenyl)-4-(tetrazol-5-ylmethyl)azetidin-2-ones to 3-Methoxy-9,9a-dihydroazeto[1,2-a]tetrazolo[5,1-d] [1,5]benzodiazepin-11(10H)-ones and