Total Syntheses of (+)-Villocarine A, (-)-Apogeissoschizine, and (+)-Geissoschizine

Total syntheses of geissoschizine-type monoterpenoid indole alkaloids (MTIAs) are reported. An intramolecular Pictet-Spengler cyclization was developed for the selective construction of the 3R stereocenter. The first total synthesis of (+)-villocarine A was then achieved. Furthermore, the first total synthesis of the highly strained (-)-apogeissoschizine was also accomplished in an aza-Michael cyclization/E1cB elimination/stereoselective olefin isomerization sequence. Finally, (+)-geissoschizine, a common biosynthetic intermediate of MTIAs, was obtained from apogeissoschizine through ring-opening along with a release of ring strain.

Total Synthesis of Ophiorrhine A, G and Ophiorrhiside E Featuring a Bioinspired Intramolecular Diels–Alder Cycloaddition**

We report the first total synthesis of the monoterpene indole alkaloids ophiorrhine A via a late stage bioinspired intramolecular Diels–Alder cycloaddition to form the intricate bridged and spirannic polycyclic system. Several strategies were investigated to construct the indolopyridone moiety of ophiorrhiside E, the postulated biosynthetic precursor of ophiorrhine A. Eventually, the Friedel–Crafts‐type coupling of N‐methyl indolyl‐acetamide with a secologanin‐derived acid chloride delivered ophiorrhine G. Cyclodehydration of a protected form of the latter was followed by the desired spontaneous intramolecular Diels–Alder cycloaddition of protected ophiorrhiside E leading to ophiorrhine A.

Catalytic Asymmetric Alkynylation of 3,4-Dihydro-β-carbolinium Ions Enables Collective Total Syntheses of Indole Alkaloids

Chiral tetrahydro-β-carboline (THβC) is not only a prevailing structural feature of many natural alkaloids but also a versatile synthetic precursor for a vast array of monoterpenoid indole alkaloids. Asymmetric synthesis of C1-alkynyl THβCs remains rarely explored and challenging. Herein, we describe the development of two complementary approaches for the catalytic asymmetric alkynylation of 3,4-dihydro-β-carbolinium ions with up to 96 % yield and 99 % ee. The utility of chiral C1-alkynyl THβCs was demonstrated by the collective total syntheses of seven indole alkaloids: harmicine, eburnamonine, desethyleburnamonine, larutensine, geissoschizol, geissochizine, and akuammicine.