Bicyclic, Tricyclic and Tetracyclic Phosphoranes

The crystal structure of the ozonide (15) reveals a symmetric, almost planar PO3 ring with two crystallographically asymmetric molecules in the unit cell.  

The reaction of 1,2-0-isopropylidene-a-D-glucofuranose phosphite (20) with (17) or hexafluorobiacetyl (22) gave (21) and (23) respectively in almost quantitative yield and the products were characterized by elemental analysis and multi-nuclear ( C, F, P) NMR. i 

A detailed NMR study of the mechanism of ribozymomimetic phos-phonylation with phosphorus acid and two oxiranes revealed consecutive formation of p-hydroxy-if-phosphonate monoesters (38a,b), di-(P-hydroxyalkyl)-H-phosphonates (39a,b), alkylene-H-phosphonates (40a,b), p-hydroxyalkylalky-lene phosphites (41a,b) and the corresponding stereoelectronically-stabilized H-tetraoxaspirophosphoranes (42a,b). The equilbrium between (41 a,b) and (42a,b) shifts towards (41a,b) at higher temperature.  

On the basis of structural variations in the hydridophosphorane it was previously suggested that the final step in this sequence was consistent with reversible formation of a sulfuranyl radical intermediate (43) followed by rate-determining sulfur-sulfur cleavage or a concerted process with a T.S. having a relatively high degree of phosphorus-sulfur bond formation . 

In the present paper the UV-initiated reactions of a series of nine hydropho-sphoranes (44-52) with dimethyl disulfide were followed by NMR. Only (44), (45) and the previously investigated (47) gave high (virtually quantitative) yields of the corresponding methylthiophosphoranes (53, 54 and 55). The lack of 

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