The structure of regilinine

Enantioselective Total Syntheses of Pentacyclic Homoproaporphine Alkaloids

“…Our retrosynthetic analysis is depicted in Scheme . Several members of the pentacyclic homoproaporphines such as (+)-regeline ( 1 ), (+)-jolantidine ( 5 ), and (+)-regelinine ( 6 ) could share the same intermediate, N -benzyloxycarbonyl (+)-jolantidine ( 9 ), in which the hydroxyl-lactol moiety of the D-ring could be realized through sequential Baeyer–Villiger oxidation of the C11–C12 bond of the ketone intermediate 10 and SmI 2 -mediated aldehyde–ester pinacol-type cyclization . With the use of a Suzuki coupling reaction to introduce a 2-aminoethyl moiety at the phenyl ring, followed by a Wittig reaction and a Pictet–Spengler cyclization, the fused C and B rings would be achieved from an enone intermediate 11 , delivering the ketone intermediate 10 .…”

“…= +93 ( c 1.0, CHCl 3 ))] in 86% yield. Swern oxidation of the hydroxyl group of (−)- 27 , followed by reduction with LiAlH 4 , afforded (+)-regelinine ( 6 ) ([α] 25 D = +110.4 ( c 1.0, CHCl 3 )) in 63% yield (two steps). Thus, we accomplished the enantioselective syntheses of six pentacyclic homoproaporphine alkaloids.…”