Slayton A. Evans

Regioselective phosphoranylation and cyclodehydration of triols with diethoxytriphenylphosphorane

Diethoxytriphenylphosphorane (DTPP) selectively diphosphoranylates the vicinal diol functional group in 1,2,4-triols affording thermodynamically stable 2,2,2-triphenyl-1,3,2-dioxaphospholanes. When subjected to thermolysis conditions, these dioxaphospholanes dissociate to form transient betaines which subsequently collapse, via 3-exo-tet extrusion of triphenylphosphine oxide, to epoxides. The structures of the 2,2,2-triphenyl-1,3,2-dioxaphospholanes are readily assessed from /sup n/J/sub /sup 31/P-/sup 13/C/ (n = 2,3) coupling constants and /sup 31/P chemical shifts. Alkyl and aryl substituents attached to the dioxaphospholane ring also induce pronounced substituent shielding effects on the /sup 31/P resonance of the phospholanes. These effects are useful in corroborating the structural assignments of the dioxyphosphoranes.

Asymmetric Synthesis of α-Amino Phosphonic Acids Employing Versatile Sulfinimines and Sulfonimines

The addition of metallophosphites to activated imino substrates such as sulfonimine 1 and sulfinimines 4 was successfully achieved. High diastereoselectivities and good yields were obtained with sulfinimine acceptors. The nucleophilic addition was applied to the development of a new methodology for the synthesis of enantiomerically homogeneous α-amino phosphonic acids.

Studies on the Base-Promoted Enantioselective Aldol Reaction between an (S,S)-2-OXO-2-Propionyl-1,3,2- Oxazaphosphorinane and Benzaldehyde

Abstract The synthesis of an (S,S)-2-oxo-2-propionyl-1,3,2-oxazaphosphorinane, via the condensation of (S)- 1 -N-isopropylbutan-2-ol (3) with methyl dichloro phosphite (CH3OPCl2) followed by the Michaelis-Arbusov condensation reaction with propionyl chloride, will be described. We will also present the results of OUT investigations which describe the nature of the aldol reaction involving the enolate of oxazaphosphorinane 5 with benzaldehyde.

Stereoselective aldol reactions via enolates of α-acylphosphonate diesters

In the reaction between the lithium enolate (2) of diethyl propionylphosphonate (1) and benzaldehyde, the syn-product (3s) is formed with high diastereoselectivity, as a result of structural rigidity caused by Li+ interactions with the phosphoryl oxygen.

Reactivity and Synthetic Utility of 1,3,2λ5-Dioxaphospholanes

Abstract The kinetics of Lewis acid-mediated decomposition and definitions of the synthetic applicability of 1,3,2λ5-dioxaphospholanes for (i) the syntheses of highly-hindered epoxides, and (ii) the stereospecific functionalizations of stereocenters in 1,2-diol arrays are described.

Oxaphosphoranylation of methyl α-D-glucopyranoside with diethoxytriphenylphosphorane. A highly stereoselective route to anhydropyranosides

Diethoxytriphenylphosphorane (DTPP) efficiently oxaphosphoranylates methyl α-D-glucopyranoside (1) to afford two isomeric 1,3,2λ5-dioxaphospholanes (2 and 3); thermolysis of the mixture of intermediates (2) and (3) affords methyl 2,3-anhydro-α-D-allopyranoside (4) and methyl 3,4-anhydro-α-D-galactopyranoside (5); however, in the presence of lithium bromide (LiBr), thermolysis of (2) and (3) is regiospecific, affording exclusively allopyranoside (4).

Dioxyphosphoranes, an Emerging Class of Versatile Reagents for Organic Synthesis

Abstract Several [sgrave]-dioxyphosphoranes have been prepared and their structural characterizations using NMR techniques support the trigonal bipyramidal conformer as the most stable for the acyclic phosphoranes. Their utility in smooth conversions of hydroxylated substrates [HO(CHR)n XH, n=2–6; X=O,S,NH] to the corresponding X-heterocycles is documented.

Does diclofenac reduce the incidence of post-ERCP pancreatitis?

Pancreatitis is the most common complication of endoscopic retrograde cholangiopancreatography (ERCP), and it occurs in as many as 30% of high-risk