Viismeier-Haack reagent

Tasneem. Viismeier-Haack reagent (haiomethyleneiminium salt). Syn/etf 2003,138-139. 

Lellouche, J.-P., Kotlyar, V. Viismeier-Haack reagents. Novel electrophiles for the one-step formylation of O-silylated ethers to O-formates. 

Martin, G. J., Poignant, S. Nuclear magnetic resonance investigations of carbonium ion intermediates. I. Kinetic and mechanism of formation of the Viismeier-Haack reagent. J. Chem. Soc., Perkin Trans. 2 1972,1964-1966. 

Since the Viismeier-Haack formyiation is feasible on electron-rich alkenes such as end ethers, it was a method of choice to prepare an a, 3-unsaturated aldehyde during the total synthesis of (+)-illudin C by R.L. Funk et al." The TES enol ether was treated with several reagent combinations (e.g., PBra/DMF/DCM), but unfortunately only regioisomeric product mixtures were obtained. However, the use of POBrs/DMF/DCM allowed the clean preparation of the desired aldehyde regioisomer in good yield. 

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