methyl (E)-2-[(3R,6'S,7'S,8'aS)-6'-ethyl-2-oxospiro[1H-indole-3,1'-3,5,6,7,8,8a-hexahydro-2H-indolizine]-7'-yl]-3-methoxyprop-2-enoate
methyl (E)-2-[(1R,6S,7S,8aS)-6-ethyl-2'-oxo-spiro[3,5,6,7,8,8a-hexahydro-2H-indolizine-1,3'-indoline]-7-yl]-3-methoxy-prop-2-enoate
(E)-2-[(1R,6S,7S,8aS)-6-ethyl-2'-oxo-7-spiro[3,5,6,7,8,8a-hexahydro-2H-indolizine-1,3'-indoline]yl]-3-methoxyprop-2-enoic acid methyl ester
(E)-2-[(3R,6'S,7'S,8'aS)-6'-ethyl-2-keto-spiro[indoline-3,1'-indolizidine]-7'-yl]-3-methoxy-acrylic acid methyl ester
methyl (E)-2-[(3R,6'S,7'S,8'aS)-6'-ethyl-2-oxo-spiro[1H-indole-3,1'-3,5,6,7,8,8a-hexahydro-2H-indolizine]-7'-yl]-3-methoxy-prop-2-enoate