Paul Wyatt

Alane - a novel way to reduce phosphine oxides

Phosphine oxides may be reduced to phosphines in excellent yield using alane — AlH3. An aqueous workup is not required.

Alane — A chemoselective way to reduce phosphine oxides

Abstract Phosphine oxides may be chemoselectively reduced to phosphines in excellent yield in the presence of several other functional groups using alane. An aqueous workup is not required.

Synthesis of achiral and homochiral dibenzo[b.f]phosphepin 5-oxides using bromine/lithium exchange. X-ray structure of (10R, 11R)-10,11-dihydroxy-10,11-dihydro-5-phenyl-5H-dibenzo[b.f]phosphepin 5-oxide

An improved synthesis of 5-phenyldibenzo[b.f]phosphepin 5-oxide by a seven step one-pot procedure and the synthesis of enantiomerically pure 5-phenyl- and 5-propyldibenzo[b.f]phosphepin 5-oxides by use of McMurry coupling, Sharpless dihydroxylation and a bromine-lithium exchange strategy is described.

Synthesis, X-ray structures and chemistry of enantiomerically pure 10,11-dihydro-5-phenyl-5H-dibenzo[b,f]phosphepine 5-oxides

Several phosphepine oxides were synthesised in optically pure form. Sharpless asymmetric dihydroxylation was used to introduce the chiral centres in all cases. Ring closure was achieved using either PhPCl2 or PrPCl2 together with a double nucleophile generated by either a double ortho-lithiation or double bromine–lithium exchange. The X-ray crystal structures of three phosphepine oxides illustrate their different conformations. The NMR spectra of several phosphepine oxides are described as is the chemistry which is shown to differ from that of acyclic phosphine oxides.

Preparation of fluorinated galactosyl nucleoside diphosphates to study the mechanism of the enzyme galactopyranose mutase

A novel latent→active phosphorylation strategy has been employed for the preparation of two fluorinated nucleoside diphosphates (compounds I and II). The strategy is based on the isomerisation of substituted allyl to vinyl glycosides which were subsequently phosphorylated by treatment with dibenzyl hydrogen phosphate, N-iodosuccinimide and a catalytic amount of trimethylsilyl triflate. This methodology is very suitable for the preparation of nucleoside diphosphates that have a modification in the saccharide moiety since the allyl moiety serves first as an anomeric protecting group, allowing for protecting-group manipulation and functionalisation of the sugar ring, but after isomerisation to the corresponding vinyl glycoside it acts as an anomeric leaving group. The 2-F and 4-F Gal-UDP derivatives I and II do not inhibit the enzyme galactopyranose mutase in the direction pyranose → furanose but both compounds have been found to inhibit the reverse reaction.

Synthesis of homochiral dibenzo[b,f]phosphepin 5-oxides using a double ortho-lithiation strategy

Abstract Enantiomerically pure chiral seven membered phosphorus heterocycles — phosphepins — have been prepared by McMurry coupling, Sharpless dihydroxylation, ortho -lithiation and reaction with PhPCl 2 or PrPCl 2 . Studies of the ortho -lithiation and of hydrolysis of phosphepinium salts are included.

Solution structures of some ‘uridine dialdehyde’ derivatives

When uridine is oxidised with periodate, the product is ‘uridine dialdehyde.’ Contrary to a previous report we have shown by 1H n.m.r. spectroscopy that in solution, this compound is not polymeric but consists of a large number of isomers in dynamic equilibrium, although even at 400 MHz the spectrum is too complicated to analyse fully. However if the 5′-OH group is not present, such as in 5′-azido-5′-deoxyuridine dialdehyde or 5′-O-trityluridine dialdehyde, only three diastereoisomeric cyclic acetals are present. The 1H n.m.r. spectrum at 400 MHz of the latter compound has been completely analysed and the identity and amounts of each of the three diastereoisomers have been determined.

Synthesis of the novel amine ( R *, R *, R *)-tris(α-methylbenzyl)amine. X-Ray crystal structures of racemic and enantiomerically pure forms

Single diastereomers of tris(α-methylbenzyl)amine were efficiently synthesised in either racemic [(±)-1] or optically pure (1) form starting from α-methylbenzylamine. The X-ray crystal structures reveal virtually flat nitrogen centres.

An efficient protocol for Sharpless-style racemic dihydroxylation

Racemic dihydroxylation of alkenes is efficiently accomplished with catalytic osmium (added as OsCl3), stoichiometric K3Fe(CN)6 and quinuclidine under conditions similar to those of the Sharpless asymmetric hydroxylation.