This personal account focuses on synthesis of polyhydroxylated piperidines, a subset of compounds within the iminosugar family. Cyclisations to form the piperidine ring include reductive amination, substitution via amines, iminium ions and cyclic nitrones, transamidification (N-acyl transfer), addition to alkenes, ring contraction and expansion, photoinduced electron transfer, multicomponent Ugi reaction and ring closing metathesis. Enantiomerically pure piperidines are obtained from chiral pool precursors (e. g. sugars, amino acids, Garner's aldehyde) or asymmetric reactions (e. g. epoxidation, dihydroxylation, aminohydroxylation, aldol, biotransformation). Our laboratory have contributed cascades based on reductive amination from glycosyl azide precursors as well as Huisgen azide-alkene cycloaddition. The latter's combination with allylic azide rearrangement has given substituted piperidines, including those with quaternary centres adjacent to nitrogen.

The i.r. spectra of a series of para-substituted acetanilides have been studied in order to correlate the C=O and N-H absorption with Hammett constants.A separation of the resonance and inductive effects has also been attempted. The results are compared with those obtained from the chemical shifts of Me and NH protons. EXPERIMENTAL 1.r. Spectra.-The spectra were recorded on a Perkin-Elmer 225 spectrometer under the following conditions : (a) solvent MeCN, KBr cell 54.5 mp, 0-lbr-solution; (b) solvent CHCl,, KBr cell 523 mp (since samples are less soluble in this solvent), ca. 0-Oh-solution; and (c) solvent Me,SO, KBr cell 25 mp, 0-2~-solution. The intensities were not measured in Me,SO since the solvent attacked the cell and thus altered the cell width during the experiment.

Pages 73-79. The reaction of cyclopropylphenylcarbinol with phosphorus tribromide at -15°g ives 4rbromo-l-phenyl-1-butene, identified by its nmr spectrum and by its conversion to trans-1phenyl-1,3-butadiene on treatment with sodium amide in liquid ammonia, rather than cyclopropylphenylcarbinyl bromide, in confirmation of the report of A. Maercker and J. D. Roberts, J.

(2S,3R,6R)-2-[(R)-1-Hydroxyallyl]-4,4-dimethoxy-6-methyltetrahydro-2H-pyran-3-ol was isolated in 18% after treating the glucose derived (5R,6S,7R)-5,6,7-tris[(triethylsilyl)oxy]nona-1,8-dien-4-one with (1S)-(+)-10-camphorsulfonic acid (CSA). The one-pot formation of the title compound involved triethylsilyl (TES) removal, alkene isomerization, intramolecular conjugate addition and ketal formation. The compound was characterized by 1H and 13C NMR spectroscopy, ESI mass spectrometry and IR spectroscopy. NMR spectroscopy was used to establish the product structure, including the conformation of its tetrahydropyran ring.

Methyl 2,3,6-tri-O-benzoyl-4-O-(tert-butyldimethylsilyl)-β-D-galactopyranoside was synthesized in 47% yield by the silylation of a partially benzoylated galactose derivative, prepared from methyl β-D-galactopyranoside. The product was characterized by 1 H-NMR, 13 C-NMR, IR and mass spectrometry.