Large-scale oxidations in the pharmaceutical industry.

In developing a process the chemist may encounter water in the roles of impurity, beneficial additive, or solvent. This chapter discusses some examples of water as solvent and cosolvent. Water may also be necessary in the crystallization of a desired hydrate. Quantitation can be straightforward if standard data points have been generated that use known amounts of water in the presence of the primary compound to be assayed. The presence of water may be inferred by thermogravimetric assay; however, any weight loss may not be specific for water. This chapter also examines some of the more subtle effects of water on processing. Some reagents react with water very quickly and exothermically. Water can enter a reaction as part of the air, solvents, reagents, or by-products of a reaction, or it can enter as a contaminant in equipment. Many reactions are essentially dehydrations, and the water generated can inhibit the desired reaction. Solvents may be selected to remove water azeotropically during the reaction.

Effects of Water

The preparation, analysis, and reactions of novel, highly stereoselective cyclopentadienyldialkoxyallyltitanium reagents, available in both enantiomeric forms, are described. Chiral monochlorotitanates are readily prepared from CpTiCl 3 or Cp.TiCl 3 and chiral 1,4-diols, which in turn are obtained from tartrate ester acetals by Grignard addition. The resulting stable seven-membered titanacycles have been analyzed by 1 H, 13 C, and 49 Ti NMR spectroscopy. The structures of two representatives, the complexes 15 and 20, are confirmed by X-ray diffraction

Enantioselective syntheses with titanium carbohydrate complexes. Part 7. Enantioselective allyltitanation of aldehydes with cyclopentadienyldialkoxyallyltitanium complexes

Chiral diphosphites have been synthesised starting from 1,2:5,6-diisopropylidene- D -mannitol, L -α,α,α,α,-tetramethyl-1,3-dioxolan-4,5-dimethanol and L -diethyltartrate. The diols react in moderate to good yields with 2,2′-bisphenoxyphosphorus chloride and 4,4′,6,6′,-tetra- t -butyl-2,2′-bisphenoxyphosphorus chloride (32–92%) to the corresponding chiral diphosphites. These compounds all exhibit C 2 symmetry and have been used as ligands in the rhodium catalysed asymmetric hydroformylation of styrene. The catalytic activity of the diphosphites strongly depends on the bulkyness of the ligand. With a bulky ligand enantiomeric excesses up till 20% have been obtained under mild reaction conditions (25–40°C, 40 bar syngas). It was found that both enantiomeric excess and regioselectivity to the branched aldehyde strongly depend on the hydroformylation reaction conditions.

Nancy L. Sear

Papers

Synthesis of 2,3-o-isopropylidene-d-glyceraldehyde in high chemical and optical purity : observations on the development of a practical bulk process

Synthesis of 2,3-O-Isopropylidene-D-glyceraldehyde in High Chemical and Optical Purity: Observations on the Development of a Practical Bulk Process.