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