Stereoselectivity in the double reductive alkylation of pyrroles: synthesis of cis-3,4-disubstituted pyrrolidines

The preparation and Birch reduction of a 1,3,4-tri-substituted pyrrole is described: the heterocycle is loaded with electron-withdrawing groups and undergoes a double reductive alkylation reaction to yield cis-3,4-disubstituted pyrrolidines

The partial reduction of heterocycles: an alternative to the Birch reduction

The partial reduction of a series of heterocycles in THF is described. By adding amine 3 as a proton source and naphthalene as an electron carrier, we were able to produce reductively alkylated pyrrolines and dihydrofurans in moderate to good yields. This reaction does not require liquid ammonia as a solvent, which may have interesting ramifications for large-scale synthesis. Moreover, we were also able to quench the reduction reactions with an acid chloride so performing a reductive acylation reaction. (C) 2000 Elsevier Science Ltd

Rearrangement of pyrrolines derived from the Birch reduction of electron-deficient pyrroles: Radical ring-expansion to substituted tetrahydropyridines

Access to the synthetically important tetrahydropyridine motif has been achieved by radical rearrangement of pyrrolines obtained from the Birch reduction of electron-deficient pyrroles

Stereoselective reductive alkylation of 2,5-disubstituted pyrroles: a role for naphthalene in the partial reduction of heterocycles

Lithium in ammonia promotes the stereoselective reduction of 2,5- disubstituted pyrroles: such reactions proceed with good levels of stereoselectivity, producing the trans-isomer. The stereochemistry of one of the reduced compounds was proven by X-ray crystallography. A mechanism is proposed which explains the stereoselectivity and a modification made to the reducing system that includes catalytic naphthalene and obviates the need for liquid ammonia. (C) 2000 Elsevier Science Ltd

The birch reduction of 3-substituted pyrroles

The Birch reduction of electron-deficient 3-substituted pyrroles is described. Use of a reductive alkylation procedure involving sodium metal in liquid ammonia gave good yields of 4-alkyl-2-pyrrolines. The identity of these products was proven by an X-ray structure of a crystalline derivative. Moreover, the pyrroles used in this study could be readily prepared by reaction of TOSMIC with acrylic amides and esters and, once the reduction was complete, the ester activating group could be easily removed to yield the corresponding N-protected β-proline derivatives