A Short Access to Chiral Non-Racemic Oxa- and Azaheterocycles by Cross-Metathesis and Pd-Catalyzed Cyclization Sequence

A concise synthesis of chiral non-racemic 2-(3-benzoyloxyprop-1enyl)tetrahydrofuran (5a), tetrahydropyran (5b), and piperidine (8) is described.Cross-metathesis of optically pure (S)-1-O-benzoyl-3-butene-1,2-diol (2) with protected 4-pentenol, 5-hexenol, and 5-hexenylamine gave the corresponding allyl alcohols (3a), (3b), and (7) in one step, respectively.PdCl 2 (MeCN) 2 catalyzed cyclization of 4a, 4b, and 7 afforded 5a, 5b, and 8 in excellent yields with high enantiomeric purity.Pd II -catalyzed reactions are valuable in stereoselective organic synthesis. 1We have recently reported that the Pd II -catalyzed reaction of chiral non-racemic , hydroxy, and -N-Boc-amino allyl alcohol occurs to give substituted tetrahydrofurans, tetrahydropyrans and piperidines with high stereoselectivity through the 1,3-chirality transfer process. 2 The syn oxy-and azapalladations occur predominantly in intra-and intermolecular reactions, 3,2d and we have achieved the stereocontrolled synthesis of natural products, such as (-)-aspergillide B, 4a (-)-diospongin B, 4b (-)-laulimalide, 4c and (+)-coniine, 2d using this reaction.cat.PdCl 2 (MeCN) 2 XH n R HO X H R n cat.PdCl 2 (MeCN) 2 XH n R HO X R n