Allylic phosphorates reduction

Synthesis of Phosphoric Acids and Their Derivatives. - A series of monoalkyl and dialkyl phosphorus acid chiral esters have been synthesised for use as carriers for the transport of aromatic amino acids through supported liquid membranes. The compounds acted as effective carriers but enantio-separation was at best moderate. A range of phosphono- and phosphoro-fluoridates have been prepared by treatment of the corresponding thio- or seleno- phosphorus acids with aqueous silver fluoride at room temperature (Scheme 1). In some cases oxidation rather than fluorination occurred. Stereospecifically deuterium-labelled allylic isoprenoid diphosphates, e.g. (1), have been synthesised from the corresponding deuterium-labelled aldehyde by asymmetric reduction, phosphorylation and Sn2 displacement with pyrophosphate (Scheme 2). ... 

Oxidation with lead dioxide in 5% phosphoric acid yielded acetaldehyde and formaldehyde. Catalytic reduction in the presence of platinum resulted in the absorption of 1.5 mole equivalents of hydrogen and the isolation, by its steam volatility, of nearly 0.6 mole of a-methylbutyric acid. The carbon skeleton of sarracinic acid was thus determined, and the accompanying hydrogenolysis (some nonvolatile acid was also obtained) established that the double bond and hydroxyl constituted an allylic alcohol moiety. Since further data (spectroscopic data would be especially valuable) were not available, Danilova and Kuzovkov (127) were limited to the conclusion that sarracinic acid could be represented by one of three possible structures (CLXIa-c) ... 

Another breakthrough came from Antilla et al., who employed a chiral phosphoric acid as an efficient catalyst for the reduction of prochiral ketones (83). As an extension of their success in the enantioselective allylation of aldehydes with allyl borate [84], they hypothesized that a chiral phosphoric could activate and direct the borane reduction of ketones. Initial studies showed that the asymmetric reduction truly works and, after screening various chiral phosphoric acids, found that 6 stands out as the most suitable catalyst. The enantioselectivity is further improved by using 4-(dimethylamino)pyridine (DMAP) as an additive (ee up to 95%) (Scheme 32.30). To gain mechanistic insight into this reduction, the authors performed several parallel B NMR experiments the results suggest that the complex formed between 6, catechol borate, and DMAP might be the real catalyst for the asymmetric reduction. 

---