[NH2:1][C@@H:2]1[C:13](=[O:14])[N:4]2[C@@H:5]([C:10]([OH:12])=[O:11])[C:6]([CH3:9])([CH3:8])[S:7][C@H:3]12.C[Si](C)(C)Cl.C(N(CC)CC)C.[C:27](OC=O)(=[O:29])C.C(O)=O.C(Cl)(=O)C.Cl.C(N(CC)CC)C.C(C(CCCC)C([O-])=O)C.[Na+:58]>O1CCCC1.CCOCC>[CH:27]([NH:1][C@@H:2]1[C:13](=[O:14])[N:4]2[C@@H:5]([C:10]([O-:12])=[O:11])[C:6]([CH3:9])([CH3:8])[S:7][C@H:3]12)=[O:29].[Na+:58]A mixture of (3S,5R,6R)-6-amino-2,2-dimethylpenam-3-carboxylic acid (6ApA, 2.2056 g., 10.21 mmole), trimethyl chlorosilane (2.615 ml., 20.42 mmole), and triethylamine (2.84 ml., 20.3 mmole) in tetrahydrofuran, (50 ml.) was stirred for 1 hour at +20 to +25° and then cooled to -70°. To this solution at -70° was added a cold (-60 to -70°) solution of formic-acetic anhydride [generated by stirring formic acid (470 mg., 10.2 mmole), acetyl chloride (0.726 ml., 10.2 mmole) and triethylamine (1.42 ml., 10.2 mmole) at -60 to -70° in tetrahydrofuran (40 ml.). The solution contained suspended triethylamine hydrochloride] and triethylamine (1.42 ml., 10.2 mmole). The temperature of the mixture was allowed to rise to +20° over ca. 1 hour and the mixture was then filtered. The filtrate and washings were stirred and a solution of sodium 2-ethylhexanoate (2 g., 12 mmole) in tetrahydrofuran (2ml.) and ether (18 ml.) was added. The white precipitate was isolated by filtration, washed with ether and dried to give sodium (3S,5R,6R)-6-formamido-2,2-dimethylpenam-3-carboxylate as a white powder (1.6127 g., 6.06 mmole), 59.4%); m.p. 238° to 242° (dec.); [α]D + 281° (H2O); νmax. 3412 (NH), 1790 (azetidin-2-one), 1677 and 1505 (CONH), 1602 cm.-1 (CO2 -); τ 1.28 (1H, d, J 9 Hz, NH), 1.90 (1H, s, HCO), 4.40 to 4.60 (2H, m, C5 -H and C6 -H), 6.01 (1H, s, C3 -H), 8.42 (3H, s) and 8.50 (3H, s) (C[CH3 ]2). (Found : C, 40.7; H, 4.3; N, 10.3; Na, 8.6; S, 11.7. C9H11N2NaO4S (266.3) requires C, 40.5; H, 4.1; N, 10.5; Na, 8.6; S, 12.0%).
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