propyl (S)-4-ethyl-3,4,7,8-tetrahydro-4-hydroxy-3,8-dioxo-1H-pyrano[3,4-c] pyridine-6-carboxylate

propyl (S)-4-ethyl-3,4-dihydro-4-hydroxy-8-methoxy-3-oxo-1H-pyrano[3,4-c]pyridine-6-carboxylate

4-ethyl-3-hydroxy-3,4,7,8-tetrahydro-1H,10H-spiro[pyrano[3,4-f]indolizine-6,2'-[1,3]dioxolan]-10-one

4-acetoxy-4-ethyl-6,6-(ethylenedioxy)-7,8-dihydro-1H-pyrano[3,4-f]indolizine-3,10(4H)-dione