Dabco → 1,4-Diazabicyclo(2.2.2)octane Dihydriodide

The 2-carboxylic acid (8c), as produced in Example 13a, was converted to the carbacephem (9a) through reaction with trimethylsilyl iodide (TMSI). Specifically, the carboxylic acid (8c) (0.726 g, 2 mM), was combined with 5 ml acetonitrile (ACN), HMDS (1.06 ml, 5 mM), and TMSI (0.72 ml, 5 mM), and the mixture was stirred for 4 hours at room temperature. DABCO (0.56 g, 5 mM) in 5 ml ACN was added and the solution stirred overnight at room temperature, yielding a DABCO-HI precipitate. Both reactions appeared normal and the DABCO reaction (elimination) gave an HPLC ratio of product to starting material of 39.1/12.0 for a conversion of about 77%. 5 ml of 1N HCl was added and the mixture stirred for 30 min. at room temperature. The pH was at 3.55. The DABCO-HI precipitate dissolved and the desired carbacephem product (9a) appeared as a precipitate. The product was filtered and washed successively with 10 ml of ACN/H2O (2/1), 5 ml of H2O, and 5 ml of ACN. Vacuum drying at 50° C. yielded 0.275 g of a nearly white solid. Yield was about 63.5%. NMR was excellent in DMSO (d-6) with trifluoroacetic acid (TFA) to dissolve.