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
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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 Na2 S2 O3 (10% w/v, 10 mL) was added. The mixture was extracted with CH2 Cl2 (3 × 20 mL) and the organic extracts were combined, dried (Na2 SO4 ) 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).
