![Graphical abstract: Visible-light photoredox catalysis: direct synthesis of fused β-carbolines through an oxidation/[3 + 2] cycloaddition/oxidative aromatization reaction cascade in batch and flow microreactors](https://lh3.googleusercontent.com/blogger_img_proxy/AEn0k_sSmWS9Xbc8mdMZGXvHB3wDqK1JdlOYYLoXnsW-IHSR-kMmfvqP255FJdvQMKd14ipH8ktVY4zkA9iesXtdqiQWj6M7NiKVA3mRYvPMTegwMiHhPWysBQSis5xCzw9e-0X6AYx_RjGX5YHolkYNZrFFUmq9QfIysKH6niKKnkPhZqkdZlJGcovPp036MdpaQIHGGc0fJxTTjmZfEsDaMs2c6A=s0-d)
.Fused β-carbolines were synthesized via a visible light photoredox catalyzed oxidation/[3 + 2] cycloaddition/oxidative aromatization reaction cascade in batch and flow microreactors. Several structurally diverse heterocyclic scaffolds were obtained in good yields by coupling of tetrahydro-β-carbolines with a variety of dipolarophiles under photoredox multiple C–C bond forming events. The photoredox coupling of tetrahydro-β-carboline with 1,4-benzoquinone was significantly faster in continuous flow microreactors and the desired products were obtained in higher yields compared to batch reactors.
Visible-light photoredox catalysis: direct synthesis of fused β-carbolines through an oxidation/[3 + 2] cycloaddition/oxidative aromatization reaction cascade in batch and flow microreactors
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Corresponding authors
a
Division of Medicinal Chemistry and Pharmacology, CSIR-Indian Institute of Chemical Technology, Hyderabad-500007, India
E-mail: ramaurya@iict.res.in
E-mail: ramaurya@iict.res.in
b
National Institute of Pharmaceutical Education and Research, Balanagar, Hyderabad-500035, India
c
Academy of Scientific and Innovative Research, New Delhi 110025, India
Org. Chem. Front., 2015,2, 1308-1312
DOI: 10.1039/C5QO00207A
http://pubs.rsc.org/en/content/articlelanding/2015/qo/c5qo00207a#!divAbstract
Jeevak Kapure
http://pubs.rsc.org/en/content/articlelanding/2015/qo/c5qo00207a#!divAbstract
Ram Awatar Maurya
Fused β-carbolines were synthesized via a visible light
photoredox catalyzed oxidation/[3 + 2] cycloaddition/oxidative
aromatization reaction cascade in batch and flow microreactors.
Several structurally diverse heterocyclic scaffolds were obtained in
good yields by coupling of tetrahydro-β-carbolines with a variety of
dipolarophiles under photoredox multiple C–C bond forming events.
The photoredox coupling of tetrahydro-β-carboline with 1,4-benzoquinone
was significantly faster in continuous flow microreactors and the
desired products were obtained in higher yields compared to batch
reactors.
Synthetic procedures General experimental procedures for the synthesis
of N-alkylated of tetrahydro-β-carbolines 1a-f: In a 25 mL round bottom
flask, tryptoline (86 mg, 0.5 mmol), α-halo carbonyls (0.5 mmol), Et3N
(50 mg, 0.5 mmol) and CH2Cl2 (5 mL) was taken and the reaction mixture
was stirred at ambient temperature for 2 h. Next the reaction mixture
was diluted with CH2Cl2 (15 mL) and washed with water. The organic layer
was dried over anhydrous Na2SO4 and evaporated to yield a crude product
which was purified by silica-gel column chromatography using ethyl
acetate/hexane in increasing polarity to yield compounds 1a-f.
General experimental procedures for the visible light photoredox
catalyzed coupling of Nalkylated of tetrahydro-β-carbolines 1a-f with
dipolarophiles 2a-g under batch conditions: In a 25 mL round bottom
flask, tetrahydro-β-carbolines 1a-f (0.1 mmol), dipolarophiles 2a-g (0.1
mmol), [Ru(bpy)3Cl2]·6H2O (0.5 mol%) and MeCN (5 mL) was taken. The
reaction vessel was kept at a distance of 10 cm (approx.) from a visible
light source (11W white LED bulb) and the reaction mixture was stirred
in open air condition until the reaction was complete (TLC). Next the
reaction mixture was concentrated to give a crude product which was
purified Electronic Supplementary Material (ESI) for Organic Chemistry
Frontiers. This journal is © the Partner Organisations 2015 by
silica-gel column chromatography using ethyl acetate/hexane in
increasing polarity to yield compounds 3a-n
General experimental procedures for the visible light photoredox
catalyzed coupling of Nalkylated of tetrahydro-β-carbolines 1a with
dipolarophiles 2a in flow microreactors: A solution of
tetrahydro-β-carboline 1a (0.2 mmol) and dipolarophile 2a (0.2 mmol) in
MeCN (5 mL) was kept in one syringe and the solutions of photocatalyst
[Ru(bpy)3Cl2]·6H2O (0.001 mmol in 5 mL MeCN) and t-BuOOH (2 mmol in 2 mL
MeCN) were taken in two separate syringes. All the three solutions were
pumped via two syringe pumps and mixed on an Xjunction and flown
through the capillary microreactor wrapped over a visible light source
(11W white LED bulb). Under stable conditions, exactly 6 mL of the
reaction mixture was collected, concentrated to yield a crude product
which was purified by silica-gel column chromatography using ethyl
acetate/hexane in increasing polarity to yield compounds 3a
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