Cl4 Journal of Organometallic Chemistry, 474 (1994) C14-Cl5 Preliminary Communication A convenient stereoselective synthesis of disubstituted alk-1-enyl phosphonates Henri-Jean Cristau, Marie-BCnCdicte Gasc and Xavier Yangkou Mbianda Laboratoire de Chimie Organ&e ENSCM (Unite’ de Recherche AssocGe au CNRS URA 458), 8 rue de I’Ecole Normale, 34053 Montpellier C&dex 1 (France) (Received December 31, 1993) zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Abstract A stereoselective synthesis of disubstituted diethyl alk-l-en- ylphosphonates has been developed via syn addition of RMgX/CuCl to alk-1-inylphosphonates. Key wora’s: Phosphonate; Stereoselective synthesis; Cuprate addition; Phosphorus Vinyl phosphonates are useful intermediates in the synthesis of biologically active compounds; for exam- ple, in the preparation of phosphomycin zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA uiu stereospe- cific epoxidation of an unsaturated phosphonate [l]. Furthermore they may undergo useful transformations as reagents for organic synthesis [2]. Few methods are known for the preparation of vinyl phosphonates; they are not easily obtained using the classical Arbuzov-Michaelis reaction [3], and so their efficient synthesis is of interest. Alk-1-enyl phospho- nates are generally prepared by the Wittig reaction of Correspondence to: Professor H.-J. Cristau or M.-B. Gasc. The addition of lithium organocuprate to diethyl TABLE 1. Synthesis of diethyl alk-1-enyl phosphonates, 2 acylphosphonates with methylene bisphosphonate [2,4], dehydration of /I-hydroxyethyl phosphonate [2], oxida- tive elimination of organosulfenyl and organoselenyl moieties from cu-sulfenyl and a-selenylalkyl phospho- nates [2], via catalytic subsitution on alk-1-enylbromide [2,5], and finally by &elimination of nitrous acid from a-nitroalkyl phosphonate [6]. Here we report a new and easy synthesis of disubsti- tuted vinyl phosphonates starting from readily available alk-1-ynyl phosphonates, 1 [7] and an excess of alkyl- or a&magnesium iodide with cuprous salt at -30°C in ether. This affords the corresponding vinyl phospho- nates 2 in good yields (Table 1). Q (1”) RMgI/CuCl R’_-C-.C_;j~OEt~, EtzO; -30°C; 6-7 h (23 NH&I/H,0 (1) (75%! 85%) R = Ott”, Ph or 4-Tol, R’= Pr” or Ph This addition is a typically regioselective and syn- addition process like the addition of organo-copper species to disubstituted alkynes [8]. The syn-stereo- selective addition of organo-copper to cr$-alkynyl phosphonate 1 has been established unambiguously by ‘H and 13C NMR spectroscopy for compounds 2a-c; the 3J coupling constants between 13C and 31P is typical of a rruns value, between 21 and 24 Hz [9] (Table 2). Compound R R’ Reaction Yield a IR cm-’ 6 31P (CDCI,, ppm) b-u . -- 2a Ott” Ph 6 77 1615 1240 17.1 2b Ott" Pr” 7 85 1620 1250 19.2 2c Ph Pr” 6 88 1610 1250 18.5 2d 4-Tol Ph I 75 1590 1250 17.6 a Isolated pure compounds. 0022-328X/94/$7.00 SSDI 0022-328X(94124598-D 0 1994 - Elsevier Science S.A. All rights reserved