(4R,4aS,5R)-6-((1-(4,5-dihydrothiazol-2-yl)azetidin-3-yl)thio)-3,5-dimethyl-7-(((pivaloyloxy)methoxy)carbonyl)-3,4,4a,5-tetrahydro-1H-pyrrolo[1,2-c][1,3]oxazine-4-carboxylic acid