(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

(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

(3a'S,4S,5'R,8'S,9'S,9a'S,10'R)-10'-allyl-2,2,2',2'-tetramethyl-7'-oxotetrahydro-5'H,7'H-spiro[[1,3]dioxolane-4,4'-[5,9]methano[1,3]dioxolo[4,5-d]oxocin]-8'-yl 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