Rhodium(I)-Catalysed Intramolecular [2+2+2] Cyclotrimerisations of 15-, 20- and 25-Membered Azamacrocycles: Experimental and Theoretical Mechanistic Studies

A new series of 20- and 25-membered polyacetylenic azamacrocycles have been satisfactorily prepared and completely characterised by spectroscopic methods. Various [2+2+2] cyclotrimerisation processes catalysed by the Wilkinson's catalyst, [RhCl-(PPh3)(3)], were tested in the above-mentioned macrocycles. The 25-membered azamacrocycle (like the previously synthesised 15-membered azamacrocyle) led to the expected cyclotrimerised compound in contrast to the 20-membered macrocycle, which is characterised by its lack of reactivity. The difference in reactivity of the 15-, 20- and 25-membered macrocycles has been rationalised through density functional theory calculations.