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Isomeric Five-Membered Ring Phosphites and Phosphates* Dorothy Z. Denney, Gwendyline Y. Chen, and Donald B. Denney Contribution f r o m the School of Chemistry, Rutgers Unibersity, New Brunswick, New Jersey 08903. Received April 2I, 1969 Abstract: A variety of ring- and phosphorus-substituted five-membered ring phosphites have been prepared. These materials exist as mixtures of cis and trans isomers which can be separated by glpc. The phosphites can be oxidized stereospecificallywith nitrogen tetroxide to give mixtures of cis and trans phosphates which are also separable by glpc. The lH and 31Pnmr spectra of these materials are reported. The 'H nmr spectra shows that the isomer present in the smallest amount in the phosphite mixtures has its ring alkyl group absorptions at lower fields than the most abundant isomer. The corresponding phosphates show much smaller differences in chemical shifts between the alkyl groups. It is suggested that the greater downfield shift of the alkyl group in the least stable phosphites is due to deshielding by the OR group on phosphorus which is cis to the alkyl group. Oxidation to the phosphates put oxygens cis to alkyl groups in both isomeric phosphates and thus deshielding occurs in either isomer. The thermodynamic equilibrium mixture of the two phosphites, 4, is 87: 13. Oxidation yields the same mixture of phosphates, 12. Partial hydrolysis changes the ratio of phosphates to 61:39. This ratio does not change on further hydrolysis. These results favor a trans relationship of the ring alkyl groups and the OCHI attached to phosphorus. Oxidation places an oxygen cis to the ring alkyl groups and thus in the phosphates steric interactions are more nearly equal than they are in the phosphites. Molecular models also support the configurational assignments. Isomeric six-membered ring phosphates are hydrolyzed without conversion into each other. Table I. 1H and 31P "r Spectral Data he chemistry of five-membered ring phosphates has received intensive study because of their biological Compd 'H Isointerest.? One of the most fascinating aspects of their no. Compound 31P0 CCH3* JHH mer,% chemistry is the very high rate of hydrolysis which they 1 Methylethylene methyl -139 1.26 6 62 exhibit relative to open chain phosphates and phosphosphite -142 1 40 6 38 phates with larger rings. It has been suggested that 2 Methylethylene -139 1.24 6 67 isopropyl phosphite -142 1.36 6 33 five-membered ring containing cyclic phosphates hy3 t-Butylethylene methyl -134 0.8P 77 drolyze by formation of a pentasubstituted intermediphosphite -142 0.94 23 ate. The major piece of evidence for this postulation 4 meso-l,2-Dimethyl-135 1.10 87 has been the finding that oxygen-1 8 is incorporated ethylene methyl -150 1.22 13 phosphite into recovered phosphate during the course of hydrol5 dl-1,2-Dimethylethylene - 140 1.22 6 ysis. Such incorporation has not been observed in methyl phosphite 1.29 6 acyclic phosphates and phosphates containing six6 Tetramethylethylene -147 1.18 membered rings. methyl phosphite 1.30 Recently Goldwhite3t4has shown that five-membered 7 1,l-Dimethylethylene -145 1.27 methyl phosphite 1.46 ring phosphites are configurationally stable as are a 8 Trimethylethylene 1.08 wide variety of other five-membered ring phosphorus methyl phosphite -137 1.37 88 compounds.5 Similar conclusions have also been -150 1.21 6 12 reached concerning six-membered ring p h ~ s p h i t e s . ~ J 9 Methylethylene methyl -16 1.40 7 61 phosphate 39 It was the purpose of this work to prepare a variety 10 Methylethylene -14 1.35 6 39 of five-membered ring phosphites, to examine the ratio isopropyl phosphate 1.38 6 61 of isomers obtained as a function of structural change, 11 t-Butylethylene methyl - 16 0 . 9 5 ~ 77 to convert them into the corresponding phosphates, phosphate 23 12 meso-1,2-Dimethylethyl- - 15 I . 30 86 and to study the course of the hydrolysis of selected ene methyl phosphate - 17 14 phosphates. The results of these studies have con13 dl-1,2-Dimethylethylene -14 1.37 6 firmed that five-membered ring phosphates hydrolyze methyl phosphate 1.39 6 by a unique mechanism and they have allowed tentative 14 Tetramethylethylene 1.34 assignment of configuration to the phosphites and phosmethyl phosphate 1.42 phates. achemica1 shifts relative to 85% HaPOa in parts per million. * Chemical shifts relative to TMS. Hydrogens of t-butyl group. Results
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Important spectral data for the series of phosphites and phosphates, 1-15, which were studied are collected (1) This research has been supported by the National Institutes of Health under GM-12625. ( 2 ) (a) F. H. Westheimer, Accounts Chem. Res., 1 , 70 (1968); (b) D. B. Boyd, J . A m . Chem. SOC.,91, 1200 (1969). ( 3 ) H. Goldwhite, Chem. Ind. (London), 494 (1964). (4) B. Fontal and H. Goldwhite, Tetrahedron, 22, 3275 (1966). (5) D. Gagnaire, J. B. Robert, J. Verrier, and R. Wolf, Bull. SOC. Chim. Frame, 3719 (1966). (6) D. Z. Denney and D. B. Denney, J . Am. Chem. Soc., 88, 1830 (1966). (7) G. Aksnes, R. Eriksen, and I
