Having studied the literature, we brought our attention to vinamidinium salts that are used to access substituted (hetero)aromatic compounds via a 1,3-disconnection logic. In 1961, Arnold obtained 2-chlorovinamidinium perchlorate by reaction of chloroacetic acid under Vilsmeier-Haack conditions. 14 Later, Gupton and others extended this approach to obtain various vinamidinium perchlorates. In 2000, Davies and colleagues developed safer vinamidinium hexafluorophosphate salts. Keeping this in mind, we decided to attempt the preparation of the previously unknown MeSO2-vinamidinium reagent 1 (Figure ). At the beginning, we were concerned that the activated methyl sulfone substituent would not be compatible with the harsh Vilsmeier-Haack conditions, but out of curiosity still decided to pursue that route. From the commercially available and inexpensive sodium methyl sulfinate, we first obtained ester 6 (Scheme 1). The subsequent saponification afforded the carboxylic acid 7. As we previously envisioned, the first experiments at the Vilsmeier-Haack reaction of acid 7 failed. At high temperatures (120-140 o C), the formation of the unidentified complex mixtures was observed, presumably due to the undesired reactions at the activated MeSO2-group. Varying the reaction conditions, however, revealed that performing the reaction at 90 °C allowed isolation of the desired compound 1 in 58% yield. Decreasing the reaction temperature further led to a reduction of the reaction yield. Compound 1 was a yellow crystalline solid stable at room temperature in air for at least one year. The structure of reagent 1 was confirmed by X-ray crystallographic analysis. 17 Scheme 1. MeSO2-pyrazole 2: patent approach vs this work. X-ray crystal structure of compound 1 (carbonwhite, oxygenred, nitrogenblue, sulphur -green). Hydrogen atoms and PF6  anion are omitted for clarity. Ellipsoids are shown at a 30% probability level.