Lewis Acid-Catalyzed Carbofunctionalization of Uncommon C,N-Diacyliminium Ions: Controlling Regio- and Enantioselectivity

Copper-Catalyzed Tunable Oxygenative Rearrangement of Tetrahydrocarbazoles

Herein, we report a general copper-catalyzed method for the tunable oxygenative rearrangement of tetrahydrocarbazoles to cyclopentyl-bearing spiroindolin-2-ones and spiroindolin-3-ones. The method demonstrates excellent chemoselectivity, regioselectivity, and product control simply by using the H2O and O2 as oxygen source, respectively. This open-flask method is safe and simple to operate, and no other chemical oxidants are required. Besides, inspired from the unique pathway of 1, 2-migration rearrangement, a highly controllable hydroxylation of indoles for the construction of C3a-hydroxyl iminium indolines was also developed. Mechanistic experiments suggest that a single-electron transfer-induced oxidation process is responsible for the tunable selectivity control.

Total Synthesis of Calanthoside, a Potential Hair Growth Stimulant: A Facile Synthetic Approach via One-Pot S- and O-Glucosidic Bond Formation

The first total synthesis of calanthoside (1), which exhibits potent proliferative activity against human hair follicle dermal papilla cells, has been achieved in seven steps with an overall yield of 43% on a gram scale starting from anthranilic acid (11). The synthetic strategy features a one-pot process involving thioglucoside bond formation via nucleophilic substitution reaction and enol-glucosylation for building the S-,O-bisdesmoside structure of 1. Moreover, the one-pot reaction showed broad substrate adaptability to several sugar donors other than d-glucose, thus affording S,O-bisglycoside intermediates in ∼84% yield.

Synthesis of azepane-fused pyrano[3,2-b]indoles by Lewis acid-catalysed oxa Diels-Alder reactions

The dihydroazepino[1,2-a]indole diones 3 are tricyclic oxindole-type enones which are readily accessible by catalytic photooxygenation of cyclohepta[b]indoles 1 followed by dehydration. Lewis acid-catalysed oxa Diels-Alder reactions of enones 3 with enol ethers 4 were developed that lead to novel tetracyclic azepane-fused pyrano[3,2-b]indoles 5, with high stereoselectivity and under mild reaction conditions.

AgNTf2 catalyzed cycloaddition of N-acyliminium ions with alkynes for the synthesis of the 3,4-dihydro-1,3-oxazin-2-one skeleton

A catalyzed process for the synthesis of the 4,6-substituted 3,4-dihydro-1,3-oxazin-2-one skeleton has been developed through cycloaddition of in situ generated acyliminium intermediates with alkynes. A range of chain N,O-acetals and terminal alkynes were amenable for this mild transformation. As a result, a series of desired cycloaddition products were obtained in moderate to good yields.

A short total synthesis of (±)-mersicarpine via visible light-induced cascade photooxygenation

A short total synthesis of the Kopsia alkaloid (±)-mersicarpine is presented. As the key step, a visible light-induced catalytic cascade photooxygenation was utilized, to convert a 3,3-disubstituted tetrahydrocarbazole intermediate, in one step, into a perhydropyrido[1,2-a]indole dione as the immediate precursor to the natural product. The synthesis of mersicarpine was achieved with an overall yield of 12% over 13 steps.