Cascade Iminium Ion Reactions for the Facile Synthesis of Quinolizidines. Concise Syntheses of (.+‐.)‐Epilupinine and (‐)‐Epimyrtine.

Abstract

EXPERIMENTAL PROCEDURESGeneral. Unless otherwise indicated, all starting materials and solvents were obtained from commercial suppliers and used without further purification. Tetrahydofuran (THF) and diethyl ether (Et 2 O) were dried by passage through two columns of activated neutral alumina, acetonitrile (CH 3 CN) was dried by passage through two columns of activated molecular sieves, and methylene chloride (CH 2 Cl 2 ) was distilled from calcium hydride. All solvents contained less than 50 ppm H 2 O by Karl Fisher coulometric moisture analysis. Reactions involving air-or moisture-sensitive reagents or intermediates were performed in flame-dried glassware under an atmosphere of dry nitrogen or argon. Flash chromatography was performed following the Still 1 protocol with ICN Biomedical ICN-SILITech 32-63d silica gel with the indicated solvents. Proton ( 1 H) and carbon ( 13 C) NMR spectra were obtained using a Varian Unity Plus (400 MHZ) or Varian Unity Plus (500MHz) spectrometer as solutions in CD 3 CN unless otherwise noted. Chemical shifts are reported as parts per million (ppm, δ) and referenced to the residual protic solvent unless otherwise noted. Coupling constants are reported in hertz (Hz).