C(#N)C.[I-:4].[Na+].Br[CH:7]1[C:16]2[C:11](=[CH:12][CH:13]=[CH:14][CH:15]=2)[C:9](=[O:10])[O:8]1.CC(OCC1CS[C@@H]2[C@H](NC(CC3SC=CC=3)=O)C(=O)N2C=1C(O)=O)=O>CS(C)=O>[I:4][CH:7]1[C:16]2[C:11](=[CH:12][CH:13]=[CH:14][CH:15]=2)[C:9](=[O:10])[O:8]1Iodophthalide was prepared immediately prior to use by mixing acetonitrile solutions of sodium iodide (1.5mmole) and bromophthalide (1.5mmole) and stirring for 3 minutes. This solution was filtered (to remove precipitated sodium bromide) into an ice cooled DMSO solution of cephalothin (1mmole), stirred 10 minutes and poured into ice water to precipitate the required ester. Yield of crude, neutral product after work up -- 90%. TLC and NMR indicate >90% ceph-3-em ester. δ (CDCl3 /trace DMSO) = 2.08 (d, 3H, --OCOCH3), 3.61 (broad s, 2H, C2--H), 3.88 (s, 2H, α-CH2), 4.6 - 5.4 (ABq + d, 3H, --CH2O-- + C6), 5.6 - 6.0 (m, 1H, C7) 6.9 - 7.4 (d, + t, 3H, thienyl aromatics), 7.5 - 8.2 (m, ca. 5H, phthalidyl aromatics and --OCHO--), 8.2 - 8.6 (2d, 1H, amide N-H). νmax (CHCl3) 3370, 2960, 1793, 1743, 1682, 1505, 1230, 982cm-1 ; λmax (EtOH) 275nm (ε, 7000)
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