(5S)-3-[(1S,2R,4aR,6R,8aS)-2-(but-2-en-2-yl)-3,4a,6-trimethyl-1,2,4a,5,6,7,8,8a-octahydronaphthalene-1-carbonyl]-5-(2-methylpropyl)-2,5-dihydro-1H-pyrrol-2-one = 3-{[(1S,2R,4aR,6R,8aS)-2-(but-2-en-2-yl)-3,4a,6-trimethyl-1,2,4a,5,6,7,8,8a-octahydronaphthalen-1-yl](hydroxy)methylidene}-5-(2-methylpropyl)-2,3-dihydro-1H-pyrrol-2-one — reaction