An Improved Method for the Preparation of N-Unsubstituted 1,4,5,6-Tetrahydrocyclopenta[b]pyrroles: Synthesis of an Azaprostacyclin Analogue and Its 7-Cyano Derivative
“…On the basis of these results, pyrroles 29 and 31 were prepared from diketone 4. Whilst the Paal-Knorr condensation to form the N-benzylpyrrole 29 proceeded in reasonable yield under standard conditions, formation of the free pyrrole (30) precursor to 31 required much more forcing conditions, a modification of Gossauer's procedure 19 eventually providing the compound in good yield. N-Benzylpyrrole 29 behaved similarly to the model analogue (26) and an intractable mixture of products was obtained under all oxidation conditions attempted.…”
Section: Pyrrole Formation and -Oxidationmentioning
“…On the basis of these results, pyrroles 29 and 31 were prepared from diketone 4. Whilst the Paal-Knorr condensation to form the N-benzylpyrrole 29 proceeded in reasonable yield under standard conditions, formation of the free pyrrole (30) precursor to 31 required much more forcing conditions, a modification of Gossauer's procedure 19 eventually providing the compound in good yield. N-Benzylpyrrole 29 behaved similarly to the model analogue (26) and an intractable mixture of products was obtained under all oxidation conditions attempted.…”
Section: Pyrrole Formation and -Oxidationmentioning
“…ref. 14). Unfortunately we were unable to effect direct aoxidation of either 9a or the N-Boc analogue 9c even though studies on compounds lacking the macrocyclic linking chain gave promising results.…”
A thirteen step route to the tricyclic ketopyrrole core of roseophilin is presented in which the final step consists of a Paal-Knorr pyrrole synthesis that proceeds with in situ oxidation.
“…Modern applications emerge continuously, and allow for instance synthesis of 1-aminopyrrole derivatives by using monoprotected hydrazines [59] or N-aminophthalimide [60] as the amine components. A variant employing amine hydrobromides in refluxing pyridine is available [61], and an efficient synthesis of cyclopenta [b]pyrroles from suitable diketones with hexamethyldisilazane (HMDS) as the ammonia equivalent in the presence of Al 2 O 3 has also been described [62]. Other useful extensions involve montmorillonite KSF clay [63], titanium isopropoxide [64] or iodine [65] as the catalysts.…”
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