Chromium-catalysed 1,2-addition aldehydes

JACOBSEN S SALEN AS A CHIRAL LIGAND FOR THE CHROMIUM-CATALYSED ADDITION OF 3-CHLORO-PROPENYL PTVALATE TO ALDEHYDES A CATALYTIC ASYMMETRIC ENTRY TO SYN-ALK- 1-ENE-3.4-DIOLS... 

The catalytic asymmetric allylation of aldehydes is another reaction that has received a great deal of attention. Both allylstannes and the less reactive allylsilanes undergo addition to aldehydes with high ee in the presence of enantiomerically pure Lewis acids and Lewis bases and asymmetric versions of the chromium-catalysed Kishi-Nozaki-Hiyama reaction utilising allyl halides have recently been developed. 

Catalysed aerobic epoxidation of the styrene-cobalt complex, followed by the addition of trimethylsilyl isothiocyanate, yields 4-phenyloxazolidine-2-thione 123 <96TL7315>. The 4-substituted 2-oxazolidinone 124 undergoes a "chromium Reformatsky" reaction with aldehydes RCHO (R = i-Pr or Ph) in the presence of chromium(ll) chloride and lithium iodide to give mainly the unusual anti-aldol products 125 in excellent dia,stereomeric excess and yield <97TL4,387>. 

The base-catalysed hydrophosphonylation of aldehydes or imines (Pudovik reaction) [58] as a convenient method was widely used for the synthesis of 1-hydrox-yalkylphosphonates. Since the pioneering work of Shibuya [50] and Spilling [51] was reported, much attention has been devoted to developing enantioselective catalysts for the synthesis of chiral 1 -hydroxy alkylphosphonates. Chiral aluminium complexes were shown to be more effective chiral catalysts [59-62]. Based on the success of using A1 (salen) and A1 (salcyen) as asymmetric catalysts, Al-Schiff base complexes [63, 64] have been developed to catalyze the asymmetric addition reaction of dial-kylphosphonates and aldehydes. Tridentate Schiff base metal complexes, such as vanadium, chromium, and iron [65], have been successfully applied in many asymmetric synthetic reactions. We noticed that Al(III) complexes could catalyse the asymmetric Pudovik reaction and these ligands could be easily synthesized [66-70]. 

---