Synthesis Of Pyrrolizines Research Articles

2-Formylpyrroles as Building Blocks in a Divergent Synthesis of Pyrrolizines

The selective functionalization of 2-formylpyrrole to provide diverse 1,2- and 1,2,5-substituted pyrroles is described. These compounds were used as versatile building blocks in a divergent synthesis of biologically valuable aza-bycyclic skeletons, such as pyrrolizine and pyrrolizidine derivatives. These bicycles were prepared following metal-free cascade synthetic approaches via regioselective intramolecular 1,3-dipolar cycloadditions and stereoselective Knoevenagel/Michael/ cyclization­ with dimethyl malonate.

1-Pyrrolidin-1-ylbuta-1,3-dienes as potential 1,5-dipoles; synthesis of pyrrolizines

Teutomerization of 1-pyrrolidin-1-ylbuta-1,3-dienes and (hetero)aromatic compounds formally containing this moiety, to the corresponding 1,5-dipoles by a concerted [1,6] hydrogen shift is followed by a 1,5-electrocyclization to give pyrrolizine derivatives.

Synthesis of pyrrolizines by intramolecular capture of 1,4-dipolar intermediates in reactions of enamines with dimethyl acetylenedicarboxylate

Solvent polarity and reaction temperature strongly influence the reactions of dimethyl acetylenedicar-boxylate (DMAD) with 1-pyrrolidinyl enamines of acyclic and cyclic ketones. Whereas DMAD and 1-[1-phenyl-2-(phenylthio)ethenyl]pyrrolidine ( 3) give only a mixture of the isomeric 1,3-butadienes ( 5) in apolar solvents, in methanol the main product is the pyrrolizine 7, together with 5. Again in methanol, DMAD reacts at 0-5° with 8, 9 and 10 to give exclusively 1:1 adducts, the pyrrolizines 11, 12 and 13, respectively, whereas at −50° 8 and 9 give 1:2 (enamine : DMAD) adducts, the pyrrolizines 14 and 15, respectively; a single crystal X-ray analysis of 14 gave the structure of the 1:2 adducts. In the same solvent methyl propiolate and 8 give only the linear Michael adduct 17. The enamine-ketone 18 reacts with DMAD in propylene carbonate at 0–5° to give, via (2 + 2)-cycloaddition and ring expansion, 19, and the linear Michael adduct 20. The mechanism of (2 + 2)-cycloaddition and pyrrolizine formation is discussed in terms of a common tied-ion pair intermediate formed in the first, rate-determining step, followed by a second solvent-dependent step.