Preparation of - and -lactams from carbamoyl radicals derived from oxime oxalate amides†

hydrogen from the solvent. The resulting peroxyl radicals, (14f,g) couple in pairs, extrude dioxygen, and generate alkoxyl radicals 15f,g that are very good H-atom abstractors and hence afford the hydroxylated products. Analogous hydroxylation sequences are well known. Iminyl radicals (PhC(H) N ) were produced as co-intermediates with the aminoacyls 10. The major product derived from this species was benzaldehyde. It is probable that the iminyl radicals abstract hydrogen from the solvent to afford the corresponding imine which was hydrolysed to benzaldehyde during work-up. In a few instances traces (<1%) of the azine (PhCH NN CHPh), formed by combination of two iminyls, was detected by GC-MS. Scheme 5 Preparation of βand γ-lactams. We also studied the thiazolidine-based OOAs as radical precursors. The photolysis of oxime oxalate amides 7a,b were first investigated using EPR spectroscopy. Fig. 2 shows the EPR spectrum obtained at 220 K for MAP sensitised photolysis of 7b. The EPR parameters of the carbamoyl radicals 10 obtained from 7a and 7b are in Table 1. The ratios of iminyl to carbamoyl were close to 1.0, as expected. The ring closed azetidinylalkyl radical 17 was not, however, observed in the accessible temperature range. A product study was also carried out in order to determine if a simple penicillin could be prepared via oxime oxalate amide methodology (Scheme 7). OOA 7b in the presence of MAP (3 M eq.) was photolysed with light from a 400 W UV lamp at 80 C in toluene for 8 h. GC-MS analysis showed a peak having the correct molecular ion (257) for the cyclised penicillin derivative 18. This was, in fact, the sole product derived from 7b because all the other components in the chromatogram stemmed from the solvent or from the MAP. The fragmentation pattern was consistant with that of the expected penicillin. The formula weight of the formamide that would be obtained from H-transfer to carbamoyl radical 16 is also 257. However, the MS did not show the (M H) ion expected for a formamide. Scheme 6 Formation of hydroxylated β-lactams. 719 O r g . B i o m o l . C h e m . , 2 0 0 4 , 2, 7 1 6 – 7 2 4 Pu bl is he d on 0 3 Fe br ua ry 2 00 4. D ow nl oa de d by T ri ni ty C ol le ge D ub lin o n 01 /0 5/ 20 14 1 2: 05 :3 2. View Article Online