Boron trifluoride etherate-assisted ring opening of ethylene oxide by a chiral organolithium: enantioselective synthesis of (R)-N-Boc-2-(2-hydroxyethyl)pyrrolidine

Total synthesis of hygrolines and pseudohygrolines

A concise two-step synthesis of all four diastereoisomeric hygrolines ((-)-hygroline (1), (+)-hygroline (2), (-)-pseudohygroline (3), (+)-pseudohygroline (4)) has been developed based on the (-)-sparteine (5)- or (+)-sparteine surrogate 11-mediated enantioselective lithiation of N-Boc pyrrolidine (6), followed by reaction of the chiral anion with (S)- or (R)-propylene oxide. Reduction of the resulting N-Boc amino alcohols furnished hygrolines and pseudohygrolines in 30% to 56% overall yields with dr's > 95:5.

Enantioselective organocatalytic intramolecular aza-Michael reaction: a concise synthesis of (+)-sedamine, (+)-allosedamine, and (+)-coniine

The intramolecular aza-Michael reaction of carbamates bearing remote alpha,beta-unsaturated aldehydes under organocatalytic conditions took place with good yields and excellent ee's when Jørgensen catalyst IV was used in the process, giving rise to the enantioselective formation of several five- and six-membered heterocycles. The developed methodology was applied to the synthesis of three piperidine alkaloids.

Ir-catalyzed allylic amination/ring-closing metathesis: a new route to enantioselective synthesis of cyclic beta-amino alcohol derivatives

Ir-catalyzed allylic aminations of (E)-4-benzyloxy-2-butenyl methyl carbonate with benzylamine using Feringa's (Sa,Sc,Sc)-phosphoramidite as a chiral ligand afforded linear-aminated achiral product N,O-dibenzyl-4-amino-2-buten-1-ol regioselectively (linear/branched = >99/1), whereas the (E)-5-benzyloxy-2-pentenyl methyl carbonate showed completely opposite regioselectivity (linear/branched = >1/99) and afforded the optically active (3R)-N,O-dibenzylated 3-amino-1-penten-5-ol with very high enantioselectivity (96% ee), which was used as a key intermediate for the effective synthesis of various cyclic beta-amino alcohol derivatives through ring-closing metathesis in high yields.

Total syntheses of the tylophora alkaloids cryptopleurine, (-)-antofine, (-)-tylophorine, and (-)-ficuseptine C

A concise, efficient and modular approach to the tylophora alkaloids is described, a family of potent cytotoxic agents that are equally effective against drug sensitive and multidrug resistant cancer cell lines. The advantages of the chosen route are illustrated by the total syntheses of the phenanthroquinolizidine cryptopleurine (1) and the phenanthroindolizidines (-)-antofine (2), (-)-tylophorine (3), and their only recently isolated congener (-)-ficuseptine C (4). The key steps consist in a Suzuki cross-coupling between a (commercial) boronic acid and a simple aryl-1,2-dihalide followed by elaboration of the resulting products into the corresponding 2-alkynyl-biphenyl derivatives 27, 33, 41 and 46. The latter undergo PtCl2-catalyzed cycloisomerizations with formation of the functionalized phenanthrenes 28, 34, 42 and 47, which were transformed into the targeted alkaloids by a deprotection/Pictet-Spengler annulation tandem. Due to the flexibility and robust character of this approach, it might enable a systematic exploration of the pharmacological profile of this promising class of bioactive natural products.

Direct sp3 C-H bond activation adjacent to nitrogen in heterocycles

Activation of sp(3) C-H bonds adjacent to nitrogen in heterocycles is an attractive transformation that is emerging as a practical method in organic synthesis. This tutorial review aims to summarize the key examples of direct functionalization of nitrogen-containing heterocycles via metal-mediated and metal-catalyzed processes, which is meant to serve as a foundation for future investigations into this rapidly developing area of research. The review covers functionalization of N-heterocycles via alpha-lithiation with alkyllithium/diamine complexes, alpha-amino radical formation, metal-catalyzed direct C-H activation, C-H oxidations and oxidative couplings, and metal-catalyzed carbene insertions.