Alkenylphosphonate

Dialkyl arylphosphonates and alkenylphosphonates are prepared by the coupling of halides or triflates with the dialkyl phosphonate 783[64l-643]. 

Isoxazolmes are good preciusors of a,fi-unsatiuated ketones.This transformadon ii nsefid for synthesis of polyenes. For example, nitnle oxide cycloaddidon chemistry is used tc prepare4-oxo-2-alkenylphosphonates, which are useful to synthesize a long polyethylenic unii via Woodworth-Errunons olefinadon fEq. 8.66. ... 

Han and Tanaka reported that Pd(0) complexes catalyze the addition of dialkyl phosphites to terminal alkynes to give alkenylphosphonates (Scheme 5-17, hydrophosphorylation) [15]. 

After formation of Pd(0) from the Pd(II) precursor, oxidative addition of the P-H bond could give a hydride complex. Insertion of the alkyne into either the Pd-P or Pd-H bond, followed by reductive eUmination, gives the product Consistent with this proposal, treatment of Pt(PEt3)3 with PH(0)(0Et)2 gave the P-H oxidative addition product 14, which reacted with phenylacetylene to give primarily (>99 1) the Markovnikov alkenylphosphonate (Scheme 5-18, Eq. 2). 

P-H oxidative addition followed by alkyne insertion into a Pd-P bond gives the re-gio-isomeric alkenyl hydrides 15 and 16. Protonolysis with diaUcyl phosphite regenerates hydride 17 and gives alkenylphosphonate products 18 and 19. Insertion of alkene 18 into the Pd-H bond of 17 followed by reductive eUmination gives the bis-products, but alkene 19 does not react, presumably for steric reasons. P-Hydride elimination from 16 was invoked to explain formation of trace product 20. 

The carbonyl group of l-oxo-2-alkenylphosphonates (57) undergoes stereoselective Wittig reaction with acylidenephosphoranes... 

Hydrophosphorylation has recently been extended to rhodium catalysts as a route to anti-Markovnikoff products.198 Thus, 3mol.% Rh(PPh3)3Cl affords the ( )-alkenylphosphonates (R = H, Ph, -Cr,I I ]3, CH2CH2CN, SiMe3, or cyclohexenyl) in high yields (>80%) at room temperature when 4,4,5,5-tetramethyl-l,3,2-dioxaphospholane-2-oxide (74) is used as the PH source (Equation (19)).199 The rate of reaction is highly solvent dependent... 

Zirconocene dichloride has been reported to serve as catalyst for the addition of dialkyl phosphorochloridates across the triple bond of terminal alkynes.159 DIBAL is used with the terminal alkyne system to generate the dialkyl 1-alkenylphosphonate products. 

Other interesting electron-deficient olefin substrates for the asymmetric conjugate addition include cr-acet-amidoacrylic ester SI,101 dimethyl itaconate S2,114 ct,/3-unsaturated sulfones S3,115 and alkenylphosphonate S4116 (Figure 8). 

Organoboron reagents are particularly well suited for 1,4-additions of aryl and vinyl groups to enones. Hayashi et al. developed a highly enantioselective Rh(I)/ BINAP-catalyzed 1,4-addition of phenylboronic acid to cyclic and acyclic enones [24] (Scheme 7.5) and 1-alkenylphosphonates [25]. 

In the asymmetric addition to alkenylphosphonate 33 (Eq. 2) [25], the yield is dependent on the amount of water present. The combination of boroxine and water (1 equiv. relative to boron) gave a high yield of the desired product 34, with 96% enantiomeric excess. The alkylphosphonate 34 can be used as a chiral building block for the synthesis of optically active alkenes, using a Horner-Emmons type of reaction. 

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