Synthesis of (+)- and (−)-dihydropinidine by diastereoselective dimethylzinc promoted allylation of 2-methyltetrahydropyridine-N-oxide with an allylboronic ester

The enantiomers of the naturally occurring alkaloid dihydropinidine 1, potential antifeedants against the pine weevil, Hylobius abietis, were prepared by diastereoselective, dimethylzinc mediated addition of pinacolyl 2-propenylboronate 14 to nitrones (R)- and (S)-2-methyl tetrahydropyridine-N-oxide 3, prepared from d- and l-alanine, respectively.

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(S)-N-(Benzoyloxy)-5-(1,3-dioxolan-2-yl)pentan-2-amineC15H21NO4[α]D20=-1.5 (c 0.4, CH2Cl2)Source of chirality: l-alanine

(S)-5-(1,3-Dioxolan-2-yl)-N-hydroxypentan-2-amineC8H17NO3[α]D20=-5.0 (c 0.12, CHCl3)Source of chirality: l-alanine

(2S,6S)-2-Allyl-6-methylpiperidin-1-olC9H17NO[α]D20=-7.8 (c 0.32, CHCl3)Source of chirality: l-alanine

(2S,6R)-2-Methyl-6-propylpiperidine hydrochlorideC9H20NClEe = 97%[α]D20=-12.6 (c 0.1, EtOH)Source of chirality: l-alanine