A Convenient Stereoselective Synthesis of (1R,2S,3R,4S)-3-(Neopentyloxy)isoborneol

A convenient preparation of (1R,2S,3R,4S)-3-(neopentyloxy)isoborneol (= (1R,2S,3R,4S)-3-(2,2-dimethyl-propoxy)-1,7,7-trimethylbicyclo[2.2.1]heptan-2-ol; 1a ), a valuable chiral auxiliary, is described. The synthesis involves six steps starting from the readily available camphorquinone ( 5 ) and gives 1a in 48% overall yield. The key step is the chemoselective hydrolysis of the less hindered 1,3-dioxolane moiety in the camphorquinone di-acetal 4 .     

Synthesis of heavily substituted 1,2-amino alcohols in enantiomerically pure form

[reaction: see text] A simple and convenient methodology for the preparation of optically pure 2-amino-2-aryl-1,1-diphenylethanols is presented. Allylamine was found to produce the ring-opening of triaryloxiranes in a regioselective and a stereospecific fashion. Removal of the allyl protecting group provided the free 1,2-amino alcohols in enantiomerically pure form.     

Tetramethylnorbornadiene, a versatile alkene for cyclopentenone synthesis through intermolecular Pauson-Khand reactions

1,2,3,4-Tetramethyl-bicyclo[2.2.1]hepta-2,5-diene (TMNBD, for tetramethylnorbornadiene) has been prepared and used successfully as an acetylene equivalent in the synthesis of substituted cyclopentenones. TMNBD is easily accessible on a multigram scale and displays excellent reactivity toward the intermolecular Pauson-Khand reaction. Conjugate additions on the resulting tricyclic compounds proceed with exquisite diastereoselectivity. The retro-Diels-Alder reaction of these TMNBD derivatives occurs under much smoother conditions than those required for its norbornadiene homologues.     

Absolute configuration of strictosidinic acid

The absolute configuration of strictosidinic acid, (2S,3R,4S)‐3‐ethenyl‐2‐(β‐d ‐glucopyranosyloxy)‐4‐{[(1S)‐2,3,4,9‐tetrahydro‐1H‐pyrido[3,4‐b]indol‐1‐yl]methyl}‐3,4‐dihydro‐2H‐pyran‐5‐carboxylate, was determined from its sodium chloride trihydrate, poly[[diaqua((2S,3R,4S)‐3‐ethenyl‐2‐(β‐d ‐glucopyranosyloxy)‐4‐{[(1S)‐2,3,4,9‐tetrahydro‐1H‐pyrido[3,4‐b]indol‐2‐ium‐1‐yl]methyl}‐3,4‐dihydro‐2H‐pyran‐5‐carboxylate)sodium] chloride monohydrate], {[Na(C₂₆H₃₂N₂O₉)(H₂O)₂]Cl·H₂O}_n. The strictosidinic acid molecule participates in intermolecular hydrogen bonds of the O—H...O and O—H...Cl types. The solid‐state conformation was observed as a zwitterion, based on a charged pyridine N atom and a carboxylate group, the latter mediating the packing through coordination with the sodium cation.     

A New Invariant of Quadratic Lie Algebras

We define a new invariant of quadratic Lie algebras and give a complete study and classification of singular quadratic Lie algebras, i.e. those for which the invariant does not vanish. The classification is related to O(n)-adjoint orbits in $\mathfrak{o}(n)$ .     

LO-phonon confinement effects on the polaron properties in semiconductor quantum-well heterostructures

Polaronic corrections are calculated for a semiconductor quantum-well heterostructure at T = 0 K. Electron coupling with confined LO-phonons is assumed on the basis of an electron-LO-phonon model Hamiltonian deduced in a previous work. Screening is ignored during the calculations, a parabolic band structure is supposed and the case of completely confined electrons with infinite potential barriers at the interfaces is considered. Finite values for the electron self-energies are obtained. Dependence of polaronic corrections on the quantum-well parameters is discussed in detail and comparison with other works on the subject is made. Good agreement with experimental data is found for the case of a GaAs-Al_xGa_1−xAs quantum well.