STEREOSELECTIVE SYNTHESIS OF BETA-HYDROXYAMINO ACIDS BY ALDOL REACTION OF ALPHA-ISOCYANOCARBOXYLATE WITH ARENE-CHROMIUM-TRICARBONYL COMPLEXES

High diastereoselectivity is obtained during the addition of ethyl isocyanoacetate 1 to chiral complexes 2 and 3. The 2-oxazoline-4-carboxylic esters are intermediates for the synthesis of \u3b2-substituted serines in a stereoconservative process

Regio and stereoselective oxiranyl ring opening of 2,3-diaryl oxiranes by LiBr/Amberlyst 15: a new stereocontrolled access to 1,2 diaryl-2-bromoalcohols

Both symmetrical and nonsymmetrical trans-2,3-diaryloxiranes are regio- and stereoselectively opened by the LiBr/Amberlyst 15 system. In the case of symmetrical trans-stilbene oxide, the synversus anti-bromohydrins ratio ranged between 88/12 and 30/70, by varying the reaction temperature from 20 to -30 °C. In the case of nonsymmetrical para-substituted trans-2,3-diaryloxiranes, the regioselectivity is determined by electronic effects. If one phenyl bears a strong electronwithdrawing group (as NO2 or CF3), the nucleophilic attack is totally on the beta-carbon with respect to the substituted phenyl ring. With one phenyl bearing a strong electron-releasing group (OCH3), the regioselectivity is reversed. Ab initio calculation at the DFT/B3LYP/6-31G* level, run on protonated epoxide structures, supports the formation of a cationic acyclic intermediate. Application of the method on ortho-methoxy and ortho-nitro 2,3-diaryloxiranes afforded the syn-bromohydrins in excellent yield, via regio- and stereoselective opening at either alpha- or beta-carbon, respectively

ASYMMETRIC-SYNTHESIS OF EPHEDRINE ANALOGS

Addition of nitromethane to the chiral chromium tricarbonyl complex of o-tolualdehyde (1) gives, under conditions of kinetic control, the nitroalcohol 2 with 3c95% of asymmetric induction. Compound 2 then gives, in 3 steps, the corresponding aminoalcohol in about 40% yield. Use of nitroethane gives the nitroalcohol with a small diastereoselectivity at C(2)-C(3) (d.e. = 30 and 55%), but analogs of ephedrine and pseudoephedrine can be obtained optically pure by chromatography

A 3-STEP SYNTHESIS OF AN ENANTIOMERICALLY PURE HALOSTACHINE ANALOG STARTING FROM ETA-6-(ORTHO-TOLUALDEHYDE)-CHROMIUM-TRICARBONYL

An optically pure (+)-S-Halostachine analogue 5a was synthesized in 57% total yield and in three steps from optically pure(-)-aR-[o-tolualdehyde]-chromium-tricarbonyl complex 2a. Various optically pure Halostachine analogues having an ortho-substituted aromatic ring and of both configurations (R and S) are thus available by this route. An X-ray structure of the intermediate complexed oxazoline 3bI allowed to confirm the model we proposed for the approach of a nucleophile on these arene complexes

New aniline containing aminoalcohols from trans (R,R) 2-(2-nitrophenyl)-3-phenyloxirane as useful intermediates for the synthesis of chiral ligands, bases and benzoxazines

New enantiopure aniline-containing amino alcohols are directly derived from trans-(R,R)-2-(2-nitrophenyl)-3-phenyloxirane,by alternative regioselective double reductions. Subsequent selective alkylation procedures and derivatizations provide a rapid and high-yielding access to different chiral ligands, bases, and benzoxazines, without loss of optical purity