The labile tert-butyldimethylsilyl esters of the azetidinones 6-8b served as the crucial synthons in the preparation of the potentially useful ylide pyridyl thio esters 18-20. These intermediates were utilized to synthesize a host of title carbapenems 25-30d, 32, and 49-53. The antimicrobial properties and DHP-I susceptibility of these carbapenems were studied with reference to thienamycin.

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4A molecular sieves 331 887 1720 a Static drying modes unless specified otherwise. E x p e r i m e n t a l SectionDesiccants. Details of the source, activation, and handling of most of the desiccants have already been described.' Reagent grade cupric sulfate was activated by heating at 320 "C for 15 h before use. Barium and calcium oxides were of reagent grade, and a fresh batch was used directly without activation.Solvents, DMF, MeZSO, and HMPT were commercial synthetic grades of 99% purity (Merck). Acetone was of analytical grade (M&B). All solvents were rigorously purified by standard methods.* HMPT and Me2SO were treated by standing over barium oxide overnight, followed by filtration, distillation from calcium hydride, and subsequent storage over 20% w/v 4A molecular sieves. MezSO had bp 74.5-75.0 O C at 12 mmHg, and HMPT had bp 89.0-89.5 "C at -3 mmHg.Commercial DMF was allowed to stand over 4A molecular sieves overnight and was filtered, distilled from phosphorus pentoxide (bp 55.8-56.0 "C at 20 mmHg), allowed to stand over anhydrous potassium carbonate, and subsequently stored over 4A molecular sieves.Analytical grade acetone was allowed to stand over anhydrous potassium carbonate for one day and then over 4A molecular sieves overnight. Fractionation gave material, bp 56.2 OC, which was not stored but used immediately. Gas chromatographic analysis of this material showed it to be free of impurities.Techniques. The procedure used for HMPT serves as an example. A stock solution of HMPT containing 2620 ppm of labeled water was prepared by the addition of 0.50 g of tritiated water, specific activity 0.5 mCi/mL, to the appropriate mass of purified rigorously dried HMPT. Aliquots of the stock solution (15.0 i 0.1 mL) were syringed directly onto the appropriate desiccant contained in a 25 mL clear-fit round-bottom flask, which was immediately stoppered. Experiments were conducted at ambient temperatures (26-30 "C). Where specified, samples were stirred magnetically. Aliquots (1.00 f 0.02 mL) were taken at time intervals as specified in Table I and assayed directly by liquid scintillation counting, as previously Where necessary, viz., in the case of colored solutions or suspected contamination by soluble desiccant residues, samples were distilled before assay. Sequential drying2 was accomplished by decanting monosiccated solvent onto a fresh charge of 5% w/v desiccant. Sampling was then effected at the time intervals given in the table footnotes. Registry No.-HMPT,During the course of pondering synthetic strategies directed toward t h e synthesis of the sesquiterpene eriolangin (1),l i t occurred t o us that t h e synthon 2 possessed a number of functional and stereochemical features potentially amenable to an expeditious resolution of this interesting problem. Mo-