Applications of Ring Closing Metathesis. Total Synthesis of (±)-Pseudotabersonine

Asymmetric Total Synthesis of (+)-Mannolide C

(+)-Mannolide C is a complex hexacyclic C₂₀ cephalotane-type diterpenoid featuring a highly strained 7/6/6/5 tetracyclic core containing eight consecutive stereocenters and two bridging lactones. The first asymmetric total synthesis of (+)-mannolide C has been accomplished by lipase-mediated resolution, Ru-complex-catalyzed double ring-closing metathesis (RCM) reactions, Ni^II -catalyzed diastereoselective Michael addition, and Mn^III -catalyzed allylic oxidation as the key transformations.

Copper(I)-Catalyzed Regioselective Asymmetric Addition of 1,4-Pentadiene to Ketones

By using commercially available 1,4-pentadiene as a pronucleophile, a copper(I)-catalyzed regioselective asymmetric allylation of ketones is achieved. A variety of chiral tertiary alcohols bearing a terminal (Z)-1,3-diene unit are generated in high (Z)/(E) ratio and high enantioselectivity. Both aromatic ketones and aliphatic ketones serve as suitable substrates. Furthermore, the reactions with (E)-C¹(alkyl)-1,4-dienes proceed in moderate yields with acceptable enantioselectivity but with low (Z,E)/others ratio, which demonstrates the partial isomerization of (E)-allylcopper(I) species to (Z)-allylcopper(I) species through 1,3-migration. Subsequent Heck reaction and olefin metathesis compensate for the low efficiency with C¹-1,4-dienes. The synthetic utility of the product is further demonstrated by a copper(I)-catalyzed regioselective borylation of the 1,3-diene group.

Bran-New Four-Molecule and Five-Molecule Cascade Reactions for One-Pot Synthesis of Pyrano[3,2-c]chromen-5-ones and Spiro[benzo[b][1,4]diazepine-2,2'-pyrano[3,2-c]chromen]-5'-ones under Catalyst- and Solvent-Free Conditions

Herein, two versatile bran-new methods have been developed for building three new kinds of complicated-framework compounds including 2,4,4-trimethyl-2-(phenylamino)-3,4-dihydro-2H,5H-pyrano[3,2-c]chromen-5-ones, 4,4,4',4'-tetramethyl-1,3,3',4,4',5-hexahydro-5'H-spiro-[benzo[b][1,4]diazepine-2,2'-pyrano[3,2-c]-chromen]-5'-ones, and 2,2,4',4'-tetramethyl-2,3,3',4'-tetrahydro-5H,5'H-spiro[benzo[b][1,4]-oxazepine-4,2'-pyrano[3,2-c]chromen]-5'-ones in a one-pot manner via four-molecule and five-molecule cascade reactions of commercially available 4-hydroxychromen-2-one, substituted anilines, and acetone. In consideration of these impressive features including no need of additional catalysts and solvents, moderate to good yields, excellent site-selectivity, and broad substrate/functional group tolerance, we believe that the two present protocols should have the potential for broad synthetic utility.

Natural Products and Their Mimics as Targets of Opportunity for Discovery

Diverse structural types of natural products and their mimics have served as targets of opportunity in our laboratory to inspire the discovery and development of new methods and strategies to assemble polyfunctional and polycyclic molecular architectures. Furthermore, our efforts toward identifying novel compounds having useful biological properties led to the creation of new targets, many of which posed synthetic challenges that required the invention of new methodology. In this Perspective, selected examples of how we have exploited a diverse range of natural products and their mimics to create, explore, and solve a variety of problems in chemistry and biology will be discussed. The journey was not without its twists and turns, but the unexpected often led to new revelations and insights. Indeed, in our recent excursion into applications of synthetic organic chemistry to neuroscience, avoiding the more-traveled paths was richly rewarding.

Stereodivergent Synthesis of Pseudotabersonine Alkaloids

An eight-step stereodivergent synthesis of enantiomerically pure (-)-14-epi-pseudotabersonine and (+)-pseudotabersonine has been developed from a common N-tert-butanesulfinyl ketimine key intermediate.

Palladium-catalyzed oxidative cyclization of aniline-tethered alkylidenecyclopropanes with O2: a facile protocol to selectively synthesize 2- and 3-vinylindoles

A facile and versatile palladium catalyzed oxidative cyclization of aniline-tethered alkylidenecyclopropanes with O₂ to selectively construct important synthetic intermediates 2- and 3-vinylindoles in moderate to good yields has been developed.

Total synthesis of (±)-20S-hydroxy-1,2-dehydro-pseudoaspidospermidine via a C–H activation/transannular cyclization strategy

A total synthesis to the pseudoaspidospermidine family via a C–H activation/transannular cyclization strategy has been accomplished.

Formal Synthesis of (+)-Kopsihainanine A and Synthetic Study toward (+)-Limaspermidine

The formal synthesis of (+)-kopsihainanine A has been achieved via stereoselective reduction of tetracyclic iminium ion intermediates (24). However, attempts to synthesize (+)-limaspermidine by reduction of the same tetracyclic iminium ion intermediates have failed. The synthesis features a Suzuki cross-coupling reaction, a cyclization reaction mediated by trifluoromethanesulfonic anhydride, and stereoselective reduction of an iminium ion.