tert-butyl (1S,4R,5S,6R)-5-[(4-methylphenyl)sulfonyl]-6-({[(1S,4R)-4,7,7-trimethyl-3-oxo-2-oxabicyclo[2.2.1]hept-1-yl]carbonyl}oxy)-7-azabicyclo[2.2.1]hept-2-ene-7-carboxylate