(4S,4bS,9aR,10aR)-5-Isopropyl-4-[1-(toluene-4-sulfonyl)-1H-indol-3-yl]-1,9,9a,10a-tetrahydro-4H,4bH-10-oxa-4a-aza-indeno[1,2-a]indene-2-carboxylic acid ethyl ester