Science of Synthesis

Whitehead, A.; Sieck, S. R.; Mukherjee, S.; Hanson, P. R., Science of Synthesis, (2005) 21, 915.

Treatment of an acylphosphonate, e.g. diethyl acetylphosphonate (‌26‌), with the Vilsmeier–Haack reagent (DMF/POCl3) stereospecifically provides (Z)-1-chloro-3-oxoprop-1-enylphosphonate ‌27‌ (‌Scheme 9‌). Small amounts of tautomerization could be achieved upon refluxing in ethyl acetate to provide a 93:7 ratio of Z/E-isomers.[‌27‌] Subsequent condensation of ‌27‌ with hydrazines in the presence of either sodium hydride or potassium carbon­ate provides substituted pyrazolylphosphonates ‌28‌. Alternatively, treatment of acylphosphonates with hydroxylamines and guanidines provides isoxazolylphosphonates and pyrimidinylphosphonates, respectively. Condensation of acylphosphonates ‌29‌ with hydrazine prior to treatment with dimethylformamide/phosphoryl chloride also successfully affords pyrazole products ‌30‌ (‌Scheme 9‌).[‌28‌,‌29‌]

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Meeeeee 8M-Meeeeee-8-eeeeeeeeeeeeee ‌88‌; Meeeeee Meeeeeeee:[‌88‌]

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References

Meeeeee Meeeeeeeeee

• 8.Meeeee-Meee, (8888) M 8e, 888.