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Vilsmeier without POCl3

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Looks like POCl3 is not the only reagent capable of creating a good enough electrophile from DMF for the Vilsmeier formylations!

(CF3SO2)2O or aka Tf2O

cited from:
Sandipan Sarkar. Trifluoromethanesulfonic (triflic) Anhydride. SYNLETT 2004, pp 000A–000B (Spotlight 82).

"Tf2O has been utilised as a mild activation reagent in Vilsmeyer–Haack formylation. Less nucleophilic aromatics can be formylated with DMF/Tf2O."

Me2N-CHO + Tf2O --[ 0°C ]--> Me2N+=CH-OTf + TfO- --[ i)+ArH; ii) aq. NaOH ]--> Ar-CHO
yield: 25-90%

Martínez, A. G.; Álvarez, R. M.; Barcina, J. O.; Cereo, S. M.; Vilar, E. T.; Fraile, A. G.; Hanack, M.; Subramanian, L. R. J. Chem. Soc., Chem. Commun. 1990, 1571.

Pyrophosphoryl chloride (P2O3Cl4)

cited from:
Pansare and Ravi. Steric and electronic effects in arene formylations involving pyrophosphoryl chloride. SYNLETT 1994, 823-824.

"A significant development has been the recent demonstrations that the use of pyrophosphoryl chloride (P2O3Cl4) in the Vilsmeier formylations offer significant advantages in both reactivity and regioselectivity over over the conventional phosphoryl chloride (POCl3) derived reagent."

Cheung et al. SYNLETT 1992, 77.
Downie et al. Tetrahedron 49, 1993, 4015.

OK, I know Tf2O and P2O3Cl4 are not cheap and easy to get but it is nice to see there are even better alternativatives to POCl3. If only tionyl chloride or P2O5 would work >:( .
Anybody else knows of other reagents for the Vilsmeier?

Post 17068 (missing) (Rhodium: "Pyrophosphoryl Chloride Vilsmeyer", Chemistry Discourse)
Post 409706 (demorol: "Preparation of pyrophosphoryl chloride", Methods Discourse)

Anybody else knows of other reagents for the Vilsmeier?

A quick TFSE search revealed the following alternatives:
Post 62910 (missing) (cesium: "Modification of Vilsmeier-Haack reaction", Chemistry Discourse)
Post 207345 (missing) (Antoncho: "Vilsmeier mechanism: the alternatives to POCl3", Chemistry Discourse)
Post 335428 (hypo: "formylation using triformamide", Novel Discourse)

Btw., POCl3 can be prepared by cautious heating of the mixture of PCl5 and P2O5 (molar ratio 3:1) until complete dissolution. Pure product can be obtained by fractional distillation of the resulting liquid.

SOCl2 will also work, as will PCl3, PBr3, MsCl, Etc. In fact, anything that can dehydrate the amide to form the haloimidate will work.

That would be very interesting!  :)
Can you provide any references which use this?


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