Nitrogen-containing π-excessive aromatic heterocycles, in particular, carbazole, indolocarbazole, benzocarbazole, and carboline are considered to be the fundamental backbone of organic chemistry for many decades due to their omnipresence in natural...
Indoles are one of the most prominent aromatic heterocycles in the organic chemistry space. Due to their widespread presence in various natural products, alkaloids, drugs, approved medicines, etc. synthesis and...
Benzannulation of 2‐alkenylindoles with readily available aldehydes, under one‐pot sequential triple‐relay‐catalysis, provides an easy access to several structurally unique carbazoles including 2‐ and 3‐alkenylcarbazoles. This protecting group‐free method enabled one‐pot synthesis of alkaloids such as hyellazole and 6‐chlorohyellazole, and the formal syntheses of seven other alkaloids. Construction of the core structure, present in murastifoline A, murrafoline E, and related alkaloids was also demonstrated. Even conjugated 3,3′‐biscarbazoles can also be synthesized by one‐pot, two‐fold sequential triple‐relay catalysis.magnified image
A one-pot, protecting-group-free
benzannulation of 2-alkenylindoles
with readily available 1,3-dicarbonyls is demonstrated to construct
structurally diverse carbazoles. The use of a cheap Brønsted
acid catalyst and air as the sole oxidant exemplifies the economic
viability of this protocol. The execution of four different reactions
successively to generate the medicinally important indolocarbazole
core is also achieved. This one-pot protecting-group-free method paved
the way for the total synthesis of three medicinally important alkaloids,
namely staurosporinone, arcyriaflavin A, and 7-hydroxy-K252c.
The synthesis of sensitive β-alkyl 3-vinylindoles having diverse functional groups with good selectivity remains a challenging task. Keeping the synthetic utility of 3-alkenylindoles in mind, we explored a unique approach to synthesize them from unprotected indoles in a domino fashion. A transition-metal-free C3-alkenylation of indole is reported by using sequential Brønsted acid/base catalysis. Several β-substituted 3-alkenylindoles and conjugated 1,3-dienes are synthesized by direct coupling of indole and readily available aliphatic aldehydes. Excellent scalability and recycling of benzenesulfinic acid for successive alkenylation reactions up to five times make this method economically viable.
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