Wesley G. Bentrude

Twist conformation for the cis N,N-dimethylphosphoramidate of thymidine 3′,5′-cyclic phosphate

Abstract PMR analysis assigns twist and chair predominant conformations to the Rp and Sp diastereomers, respectively ( 3 a and 3 b ), of thymidine 3′,5′-cyclic N,N-dimethylphosphoramidate, 3 . The twist conformer population of 3 a is about 64 (acetone) to 75% (toluene).

Preparation of diastereomeric thymidine 3′,5′-cyclic methylphosphonates. Assignment of RP and SP configurations by 13C NMR

Abstract The diastereomers of thymidine 3′,5′-cyclic methylphosphonate have been prepared and separated. A use of 13 C NMR for the assignment of their phosphorus configurations is demonstrated which should be generally applicable to P-derivatized cyclic nucleotides.

Photorearrangements of benzyl phosphites. Stereochemistry at phosphorus

Abstract The photo-Arbuzov rearrangement of a cyclic benzyl phosphite is shown to proceed with retention of configuration at phosphorus. The mechanistic and potential synthetic implications of this result are discussed.

Facile preparation of the individual diastereomers of thymidine 3′,5′-cyclic phosphorothioate (cTMPS)

A facile synthesis of the individual Sp and Rp 3,5-cyclic thymidine phosphorothioates is reported. The key intermediate is a methyl phosphite triester which is readily converted under free-radical conditions to the diastereomeric thiophosphates which are separated on SiO2 and then cleanly dealkylated by t-BuNH2, to the ami ne salts of title compounds.

Pentacovalent phosphorus-containing model of a P(V) cyclic nucleotide intermediate. Non-chair conformation of the phosphorus-containing ring

Abstract A cyclic nucleotide model system ( 3 ) for P(V) cAMP-substrate or cAMP-enzyme adducts is shown by 1 H NMR analysis to be totally in a twist conformation ( 3b ).

Nucleoside analog-based phosphonates via photochemical, single electron transfer (SET) induced rearrangements of allyl phosphites

Abstract The photochemical SET rearrangement of nucleoside analog-based phosphites 12 and 13 , initiated by the singlet excited state of DCN, affords the corresponding diethyl phosphonates 14 and 15 . Deprotection of 15 gives phosphonate 16 . Treatment of 14 – 16 with base yields the vinylphosphonates 17–19 as the ( E )- and ( Z )-diastereomers.

Effect of nitrogen substituents on the relative energies of twist and chair-form conformations of CIS 2-oxo-2-dimethylamino-5-t-butyl-1,3,2-oxazaphosphorinanes

Abstract Replacement of the phenyl substituent on nitrogen of the 1,3,2-oxaza ring of the title compounds changes the twist-chair equilibrium such that the chair conformation is populated rather than the twist form primarily occupied in the N-phenyl case. A possible rationale based on Me 2 N-phenyl interactions is proposed.

PHOTOCHEMICAL SET INDUCED 1,4-CONJUGATE ADDITIONS OF SILYL PHOSPHITES TO CYCLIC ENONES

Abstract Irradiation of cyclic enones 5–8 in the presence of Me3SiOP(OMe)2 or Me3SiOP(OEt)2 gives phosphonosilylation products of 1,4-conjugate addition which are hydrolyzed to the phosphonoketones 11–14 in 82–92% isolated yields. An SET process in which the triplet enone accepts an electron from the silyl phosphite is proposed to be the key initiation step in these reactions.

X-RAY CRYSTALLOGRAPHIC STUDY OF PHOSPHORANES. EFFECTS ON EQUATORIAL O–P–O BOND ANGLES OF INCLUSION OF PHOSPHORUS IN A 1,3,2-DIOXAPHOSPHORINANE RING

Abstract The crystal structures of phosphoranes 8 and 10 have been determined. Phosphorane 8 crystallizes in a monoclinic space group P21/c with a = 10.664 (1) A, b = 12.782 (2) A, c = 18.121 (1) A, β = 91.67 (1)°, and Z = 4. Phosphorane 10 crystallizes in a monoclinic space group P21/n with Z = 4, a = 7.014 (1) A, b = 34.019 (7) A, c = 9.022 (3) A, and β = 111.24 (2)°. Phosphoranes 8 and 10, with phosphorus included in a bicyclic ring system, feature a distorted trigonal-bipyramidal (TBP) local geometry about phosphorus. Determined were apical bond angles: O–P–O, 162.5 (1)° (8) and 163.3 (1)° (10) and equatorial bond angles: O–P–O. 107.7 (1)° (8) and 112.7 (1)° (10). These results suggest that compression of the equatorial O–P–O bond angle in the six-membered ring of 8 and related phosphoranes to allow pucker of the ring to assume a chair conformation may occur more easily than when phosphorus is not also part of the bicyclic ring system of 8 and 10.

CONFORMATIONS OF SATURATED SIX-MEMBERED-RING PHOSPHORUS HETEROCYCLES. SYNTHESES AND X-RAY CRYSTAL STRUCTURES OF THREE 2-ANILINO-2-OXO-5,5-DIMETHYL-1,3,2-OXAZAPHOSPHORINANES

Abstract Single-crystal X-ray structural determinations have been made on 2-anilino-2-oxo-5,5-dimethyl-1,3,2-oxazaphosphorinane. 1; 2-(4-fluoroanilino)-2-oxo-5,5-dimethyl-1,3,2-oxazaphosphorinane. 2; and 2-(4-dimethylaminoanilino)-2-oxo-5,5-dimethyl-1,3,2-oxazaphosphorinane, 3. Compounds 1 and 2 are iso-structural and crystallize in the monoclinic space group P21/c with four molecules per unit cell. The cell dimensions for 1 are: a=12.234(4) A, b=8.891(3) A, c=12.152(4) A, and B=110.77(4)°. The cell dimensions for 2 are: a=12.505(1) A, b=8.919(1) A, c=12.211(1) A, and B=109.14(1)°. Compound 3 crystallizes in the monoclinic space group P21/c with four molecules per unit cell of dimensions a=6.321(2) A, b=19.963(3) A, c=12.236(2) A, and B=104.89(4)°. Full-matrix least-squares refinement for each of the structures led to conventional R factors of 5.1% for 1, 4.9% for 2, and 9.5% for 3. The conformation adopted by 1 and 2 is the chair conformation with the anilino substituent axial. Compound 3 adopts the alte...