Naturally occurring carbazole alkaloids including 2‐hydroxy‐3‐methylcarbazole, pyrano[3,2‐a]carbazole alkaloids (girinimbine and murrayacine) and prenylcarbazole alkaloids (mukoenine‐A and heptaphylline) have been synthesized on gram scale. The key compound in these syntheses is 9‐benzyl‐2‐methoxy‐3‐methylcarbazole, which was prepared by an efficient Au‐catalyzed cyclization reaction of readily available methoxypropadiene and indole‐2‐carbaldehyde. Girinimbine and murrayacine were synthesized by a concise PhB(OH)2‐mediated intermolecular cyclization with 3‐methylbut‐2‐enal. Palladium‐catalyzed allylation/Claisen rearrangement proved to be the best route to mukoenine‐A and heptaphylline.

Olefins, compounds with a carbon-carbon double bond, are of fundamental importance, and stereodefined construction of tetrasubstituted carbon-carbon double bond is a significant challenge. Here we show a unique and practical method for the preparation of stereodefined, fully substituted olefins via conjugate addition of organozinc reagents to readily available 2,3-allenals. Through mechanistic studies, it is confirmed that the geometry of the newly formed double bond is controlled by unique regiospecific oxygen-protonation of the enolate intermediates, generating 1,3-alkadienols. Such alkadienols would undergo a concerted 1,5-H-transfer reaction via a six-membered transition state to ensure the configuration of the carbon-carbon double bond in the final products. Using the readily available organozinc reagents and 2,3-allenals provides a very rapid access to a wide range of tetrasubstituted olefins with defined stereochemistry, bearing an extremely versatile aldehyde functionality.

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Chiral molecules, which may contain one or more different type(s) of stereocentres, such as central, axial, planar, and helical chiralities, etc., are indispensable in chemistry, pharmaceutical industry, and life science. Despite many advances for the preparation of chiral molecules usually with a single type of chirality have been realized, simultaneous construction of different types of chiralities is still a significant challenge. Here, we wish to report a protocol for preparation of chiral allenes with both central and axial chiralities via a catalytic asymmetric allenylation of different biologically or synthetically useful fluorinated or non-fluorinated nucleophiles with readily available racemic allenes by using a single chiral ligand. An echoing between the central chirality and axial chirality for the enantioselectivity was observed. This strategy provides a general and practical approach to functionalized optically active allenes bearing both central and axial chiralities with an excellent enantioselectivity under mild conditions.

A general N-heterocyclic carbene (NHC)-promoted annulation reaction of allenals with chalcones affording polysubstituted pyranyl aldehydes has been developed. Three mechanistic possible pathways have been proposed. The NHC attacks the center carbon of allenals or acts as a base for deprotonation and then undergoes a 1,4-addition with chalcones, followed by sequential reactions giving the final products.