P4O10/TfOH mediated domino condensation-cyclization of amines with diacids: a route to indolizidine alkaloids under catalyst- and solvent-free conditions

A domino condensation–cyclization method is developed to synthesize indolizidine alkaloids using a P₄O₁₀/TfOH reagent system without the employment of either a catalyst or solvent. The use of a few aliphatic and aromatic dicarboxylic acids is shown along with various primary amines. This method is suitable for synthesizing pyrrolo[2,1-a]isoquinolines, pyrido[2,1-a]isoquinolines, and isoindolo[1,2-a]isoquinolinones in excellent yields. When phthalic acid is used, a workup with either NaBH₄ or a saturated NaHCO₃ solution provided 12b-H or 12b-OH isoindolo[1,2-a]isoquinolinones, respectively.

A highly efficient and direct methodology for the construction of pyrrolo[2,1-a]isoquinoline, pyrido[2,1-a]isoquinoline, and 12b-H and 12b-OH isoindolo[2,1-a]isoquinolinone alkaloids from commercially available synthons is devised.

Electrophilic Aminating Agents in Total Synthesis

Classical amination methods involve the reaction of a nitrogen nucleophile with an electrophilic carbon center; however, in recent years, umpoled strategies have gained traction where the nitrogen source acts as an electrophile. A wide range of electrophilic aminating agents are now available, and these underpin a range of powerful C-N bond-forming processes. In this Review, we highlight the strategic use of electrophilic aminating agents in total synthesis.

Combined Enzyme- and Transition Metal-Catalyzed Strategy for the Enantioselective Syntheses of Nitrogen Heterocycles: (-)-Coniine, DAB-1, and Nectrisine

The enantioselective syntheses of (-)-coniine, DAB-1, and nectrisine have been developed, utilizing a complementary strategy of enzyme- and transition metal-catalyzed reactions. The initial stereocenter was set with >99% enantioselectivity via an enzyme-catalyzed hydrocyanation reaction. Substrate incompatibilities with the natural enzyme were overcome by tactical utilization of ruthenium-catalyzed olefin metathesis to functionalize an enzyme-derived (R)-allylic fragment. The piperidine and pyrrolidine alkaloid natural products were obtained by a route that leveraged regio- and stereoselective palladium-catalyzed 1,3-substitutive reactions.

Pyrrolizidine alkaloids: occurrence, biology, and chemical synthesis

Covering: 2013 up to the end of 2015This review covers the isolation and structure of new pyrrolizidines; pyrrolizidine biosynthesis; biological activity, including the occurrence of pyrrolizidines as toxic components or contaminants in foods and beverages; and formal and total syntheses of naturally-occurring pyrrolizidine alkaloids and closely related non-natural analogues.

Total synthesis of (−)-(6R,11R,14S)-colletallol via proline catalyzed α-aminoxylation and Yamaguchi macrolactonization

A simple and efficient synthesis of 14-membered macrolide (−)-(6R,11R,14S)-colletallol was achieved in a highly diastereoselective manner using proline catalyzed alpha-aminoxylation and Yamaguchi protocol.

Novel stereocontrolled syntheses of tashiromine and epitashiromine

A novel stereocontrolled approach has been developed for the syntheses of tashiromine and epitashiromine alkaloids from cyclooctene β-amino acids. The synthetic concept is based on the azetidinone opening of a bicyclic β-lactam, followed by oxidative ring opening through ring C-C double bond and reductive ring-closure reactions of the cis- or trans-cyclooctene β-amino acids.

Divergent synthesis of various iminocyclitols from d-ribose

A very efficient route to the diastereoselective synthesis of polyhydroxy pyrrolidines, piperidines and azepanes from an aldehyde derivative of ribose is reported.

Enantioselective syntheses of (R)-pipecolic acid, (2R,3R)-3-hydroxypipecolic acid, β-(+)-conhydrine and (−)-swainsonine using an aziridine derived common chiral synthon

Concise total syntheses of (R)-pipecolic acid, (2R,3R)-3-hydroxypipecolic acid and formal syntheses of β-(+)-conhydrine, (−)-lentiginosine, (−)-swainsonine and -1,2-di-epi-swainsonine have been accomplished starting from a common chiral synthon.

A stereocontrolled synthesis of Hagen's gland lactones via iterative proline catalyzed α-aminoxylation and oxa-Michael addition reactions

A simple and efficient synthesis of Hagen's gland lactones was achieved using a sequential α-aminoxylation/oxa-Michael approach in a highly diastereoselective manner with assignment of relative configurations.