(S)-2-(dimethylamino)-2-oxo-1-((3aS,4R,7S,7aS)-2,2,2',2'-tetramethyl-6-methylenetetrahydro-5H-spiro[benzo[d][1,3]dioxole-4,4'-[1,3]dioxolan]-7-yl)ethyl pivalate

(S)-2-(dimethylamino)-2-oxo-1-((3aS,4R,7S,7aS)-2,2,2',2'-tetramethyl-6-oxotetrahydro-5H-spiro[benzo[d][1,3]dioxole-4,4'-[1,3]dioxolan]-7-yl)ethyl pivalate

(S)-2-(dimethylamino)-1-((3aS,4R,6S,7S,7aS)-6-hydroxy-2,2,2',2'-tetramethyltetrahydro-5H-spiro[benzo[d][1,3]dioxole-4,4'-[1,3]dioxolan]-7-yl)-2-oxoethyl pivalate

(6R,7S,7aS)-7-((tert-butyldimethylsilyl)oxy)-2',2'-dimethyl-2,4-dioxo-4,5,7,7a-tetrahydro-2H-spiro[benzofuran-6,4'-[1,3]dioxolan]-3-yl pivalate

2,2-Dimethyl-propionic acid (S)-5-[(S)-(tert-butyl-dimethyl-silanyloxy)-((R)-2,2-dimethyl-[1,3]dioxolan-4-yl)-methyl]-4-(2-diazo-acetyl)-2-oxo-2,5-dihydro-furan-3-yl ester