Piotr P. Graczyk

Synthesis and conformation of 2-dimethoxyphosphoryl-1,3-diselenanes. The first evidence for SeCP anomeric interactions.

Abstract Analysis of the 1 H and 13 C NMR spectra of conformationally labile 2-dimethoxyphosphoryl-5,5-dimethyl-1,3-diselenane and equilibration of the diastereoisomeric cis - 2 and trans - 2 revealed that the anomeric effect of magnitude about ΔG° A E =10 kJmol −1 is operating in SeC- system. Crystallographic data are in accord with the interplay of the n S e -σ* C − P negative hyperconjugation and repulsive interactions between lone electron pairs on phosphoryl oxygen and lone pairs on the endocyclic selenium atoms in trans - 2 .

Conformation of 2-phosphoryl and 2-thiophosphoryl 1,3-dithianes and related compounds. Comments on the origin of S-C-P anomeric interactions.

A relationship was found between the γ-effect values in 13C NMR spectra and the solution conformation of the title compounds. Base-catalyzed equilibration of anancomeric 2-phosphoryl and 2-thiophosphoryl substituted 5-t-butyl-1,3-dithianes showed that axial preference increases in the order: Ph2P(S)<Ph2P(O)<(MeO)2P(O). Explanation of this phenomenon is proposed, based also on the results of molecular mechanics calculations.

A solution and solid state conformation of 2-diphenylphosphinoyl-1,3-dioxanes. The nature of O-C-P anomeric interactions.

Abstract Diastereoisomeric 2-diphenylphosphinoyl-1,3-dioxanes 1–4 were synthesized either via the Arbuzov reaction of isopropyl diphenylphosphinite with (1,3-dioxan-2-yl) trimethylammonium iodides or via the transacetalization reaction between 1,3-diols and diphenyl (diethoxymethyl) phosphine oxide. The latter reaction afforded less thermodynamically stable isomers of 3 and 4 in a good yield (44 and 56%, respectively). The magnitude of the anomeric effect in this system determined according to the Francks equation was found to be 19.7 kJ/mol. Both the NMR and X-ray structural data concerning cis -4,6-dimethyl-1,3-dioxane derivatives 4 suggest that the anomeric effect could stem from several interaction, including the n o -δ * C-P negative hyper-conjugation and intramolecular hydrogen bond formation.

Synthesis of 1-diethoxyphosphoryl-1-methylthio-thioacetamides and 1-methylthioethenethioamides. An unusual intramolecular α-desulfenylation of thioacetamides

Abstract Addition of the lithiated α-phosphoryl sulfide 1-Li to alkyl or aryl isothiocyanates 4(a–f) and phenyl isocyanate 4g was found to afford 1-diethoxyphosphoryl-1methylthio-thioacetamides 5(a–f) and -acetamide 5g , respectively. In the case of the reaction with the p-chlorophenyl isothiocyanate 4e , the α-desulfenylated product 6 was isolated and on the basis of 31 P-NMR experiments a mechanism of its formation was proposed. The phosphonates 5(a–f) , which exist in the thione form, were found to undergo the Horner-Wittig reaction with aromatic aldehydes affording 1-methylthioethenethioamides 14(a–f) .

CONFORMATIONAL PREFERENCE IN 1,3-DITHIANES CONTAINING PHOSPHONIUM AND PHOSPHINO SUBSTITUENTS AT THE ANOMERIC CARBON ATOM

Abstract The synthesis and conformational analysis of 1, 3-dithiane, 5,5-dimethyl-1,3-dithiane, 5-tert-butyl-1,3-dithiane and 4,6-dimethyl-1,3-dithiane containing different phosphonium and phosphino groups at the anomeric carbon atom are described.

A solution and solid state conformation of 2-phosphoryl substituted 1,3-oxathianes

Abstract Analysis of 1 H, 13 C and 31 P NMR spectra of 2-dimethoxyphosphoryl and 2-diphenylphosphinoyl-substituted 1,3-oxathianes revealed that they exist in solution almost exclusively in a chair conformation with the phosphoryl group being equatorial. The equatorial orientation of the Ph 2 P(O)-group in 2-(diphenylphosphinoyl)-5,5-dimethyl-1, 3-oxathiane was also found in the crystal state.

SOLID STATE CONFORMATION OF THE ANOMERIC EFFECT IN 2-PHOSPHORYL-, 2-THIOPHOSPHORYL- AND 2-SELENOPHOSPHORYL-SUBSTITUTED 1,3-DITHIOLANES

Abstract The crystal structure of the title compounds 1–3 have been determined by X-ray diffraction studies. The 1,3-dithiolane ring in all three compounds adopts a twist conformation with the Ph2P=X group being pseudoaxial. The structural data suggest that the ns → σC-P* negative hyperconjugation is responsible for the anomeric effect in 1,3-dithiolanes.

OPERATION OF THE GENERALIZED ANOMERIC EFFECT IN SOME 2-PHOSPHONIO-1,3-DITHIANES. STRIKING DIFFERENCE BETWEEN S-C-P+ AND O-C-N+ SYSTEMS

Abstract Both equilibration of diastereoisomeric 2-phosphonio-1,3-dithianes and NMR studies on conformationally labile models reveal the operation of the generalized anomeric effect in S-C-P+ system. This finding is in a sharp contrast with O-C-N+ systems, for which the reverse anomeric effect has been postulated.

Lack of manifestation of the exo-anomeric effect in SCP(:) System

The absence of the shielding effect of the phenyl ring in 2-phosphino-1,3-dithianes containing axial Ph(R)P(:) group (R= Me, Ph), as well an a large (7–8 Hz) coupling constant between axial phosphorus and carbons C(4,6) suggest the endo position of the phosphorus lone electron pair. The exo-anomeric effect, which could be governed by np-σ* c-s negative hyperconjugation is not manifested in this system. The observed rotational behavior can be sufficiently explained on steric grounds.

Unexpected mechanism of epimerization of 2-methylthiophosphonio-1,3-dithianes involving a reversible CP bond cleavage.

Abstract Diastereoisomeric 2-methylthiophosphonio-1,3-dithianes undergo spontaneous epimerization at the anomeric carbon C(2). A very low kinetic H/D isotope effect at C(2) and cross - experiments with two pairs of variously substituted 2-methylthiophosphonio - 1, 3-dithianes strongly support a dissociative mechanism of epimerization involving the C  P bond breaking.