The synthesis of veratramine

First Direct Synthesis of Optically Active 3‐Methylcyclopentene

“…'H-NMR-shift experiments with E~(tfc),~) confirmed the [a]-value given by Masamune et al [39] for optically pure material (see Table 2). This For chemical reasons we had to base our synthesis on the Rarnherg-Backlund reaction [41].…”

“…Since no correct [a]-values of (+)and (-)-13 were known, the exact rotations of optically pure 13 had first to be ascertained. 'H-NMR-shift experiments with E~(tfc),~) confirmed the [a]-value given by Masamune et al [39] for optically pure material (see Table 2). This value was furthermore corroborated chemically since (+)-5 and (-)-13 provided the optically active dibromide 8 with identical absolute rotations (cj: Exper.…”

The Chemistry and Biology of Nakiterpiosin – C-nor-D-Homosteroids

“…Masamune et al 7 and Johnson et al 8 reported in 1967 the first synthesis of 11-oxo- 3 and 4 , respectively. Masamune and co-workers had also shown previously that 3 could be obtained from 11-oxo- 3 using a Wolff reduction.…”

“…Masamune and co-workers first converted ketone 13 into a benzylic bromide and introduced the Ering of 3 using an enamine alkylation reaction. 7 Johnson and co-workers introduced the side chain of veratramine ( 4 ) to ketone 13 through a Johnson–Corey–Chaykovsky epoxidation, an epoxide–aldehyde rearrangement, and a Strecker reaction. 8a …”

Formation of Aromatic Rings through Enamine Annulation

“…Ketones, varying in structure, were used to generate the corresponding aromatic derivatives. For ketones in entries 1−6, the corresponding enamine was prepared by refluxing (3 h) an anhydrous benzene solution of the ketone (1−2 mmol), pyrrolidine (2 equiv), and catalytic amounts of p -toluenesulfonic acid (PTSA) with a modified Dean−Stark apparatus . For ketones in entries 7 and 8, enamine formation required a longer reaction time (30 h) and a larger excess of pyrrolidine (10 equiv) .…”