The transformation of 4 into the desired compounds of type 6 proceeded under acidic conditions via an oxazolinium-5-one 5 (muenchnone) which was opened by a nucleophile, as illustrated in Scheme 3 [4].

The muenchnones were also applied to 1,3-dipolar cycloadditions, e.g., with acetylene dipolarophiles of which the products are pyrrole derivatives.

Procedure [3]

The cyclohexenamide product of the Ugi reaction carried out as described in the previous section (0.05 mmol) was azeotropically dried several times (toluene) and then dissolved in 1 mL of dry toluene. The acetylene component as dipolarophile (0.25 mmol) was added aNC + R4COOH

Scheme 2

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