Iodine-Catalysed Bohlmann-Rahtz Cyclodehydration Reactions

Abstract

The cyclodehydration of Bohlmann-Rahtz aminodienones is catalysed by iodine in ethanol at room temperature to give 2,3,6-trisubstituted pyridines in excellent yield, with total regio­control and without the need for chromatographic purification.

Key words

pyridines - enamines - heterocycles - Bohlmann-Rahtz

References

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17

General Procedure for the Catalytic Cyclodehydration of Aminodienones 3 Using I ₂ . A solution of aminodienone 3 (0.2 mmol, 1 equiv) and iodine (0.04 mmol, 20 mol%) in EtOH (4 mL) was stirred at r.t. for 30 min and an aq solution of Na₂S₂O₃ (10% w/v, 10 mL) was added. The mixture was extracted with CH₂Cl₂ (3 × 20 mL) and the organic extracts were combined, dried (Na₂SO₄) and evaporated in vacuo to give pyridine 4.

18

Pyridines 4a-h exhibited physical and spectroscopic properties that were in agreement with literature data (see refs. 1, 8, 11a, and 15b for detailed information).