[(2H-AZIRIN-2-YL)METHYL]PHOSPHONATES - SY NTHESIS FROM ALLYLIC ALPHA-HYDROXYPHOSPHONATE AND GAMMA-HYDROXYPHOSPHONATE AND APPLICATION TO DIASTEREOSELECTIVE FORMATION OF SUBSTITUTED [(AZIRIDIN-2-YL)METHYL]PHOSPHONATES

Various substituted (3-azido-1-alkenyl)phosphonates 3 (R(3) = alkyl) o r their equilibrium mixtures with the regioisomeric alpha-azidophospho nates 4 (R(3) = Ph) have been synthesized from allylic alpha- or gamma -hydroxyphosphonates 2 or 1 by Mitsunobu reaction with TPP/DEAD/HN3, a nd converted into the new [2H-azirin-2-yl)methyl]phosphonates 6 upon h eating in toluene with DBU catalysis. The transformation 3/4 --> 6 pro ceeds via base-catalyzed rearrangement to the (3-azido-2-alkenyl)phosp honates 5 and subsequent thermolysis. Reduction of the 2H-azirines 6 w ith NaBH4 in methanol at 5 degrees C results in the predominant format ion of the disubstituted aziridines cis-7. Addition of trimethylsilyl cyanide to compounds 6 yields stereoselectively the highly functionali zed aziridines trans-8, while NaOCH3-catalyzed addition of dimethyl ph osphite proceeds with even higher selectivity to yield the bisphosphon ates trans-9 with excellent yields.