The direct anti-Markovnikov addition of mineral acids to styrenes

The direct anti-Markovnikov addition of strong Brønsted acids to alkenes remains an unsolved problem in synthetic chemistry. Here, we report an efficient organic photoredox catalyst system for the addition of HCl, HF and also phosphoric and sulfonic acids to alkenes, with complete regioselectivity....

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Bibliographic Details
Published in:Nature chemistry 2014-08, Vol.6 (8), p.720-726
Main Authors: Wilger, Dale J., Grandjean, Jean-Marc M., Lammert, Taylor R., Nicewicz, David A.
Format: Article
Language:English
Subjects:
639/638/403/933
639/638/77/890
Acids
Alkenes
Alkenes - chemistry
Analytical Chemistry
Biochemistry
Catalysis
Chemistry
Chemistry/Food Science
Halogenation
Hydration
Hydrogen
Hydrogen - chemistry
Inorganic Chemistry
Organic Chemistry
Oxidation
Oxidation-Reduction
Physical Chemistry
Pyridines - chemistry
Salts
Styrenes - chemistry
Sulfonic Acids - chemistry
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Summary:The direct anti-Markovnikov addition of strong Brønsted acids to alkenes remains an unsolved problem in synthetic chemistry. Here, we report an efficient organic photoredox catalyst system for the addition of HCl, HF and also phosphoric and sulfonic acids to alkenes, with complete regioselectivity. These transformations were developed using a photoredox catalyst in conjunction with a redox-active hydrogen atom donor. The nucleophile counterion plays a critical role by ensuring high reactivity, with 2,6-lutidinium salts typically furnishing the best results. The nature of the redox-active hydrogen atom donor is also consequential, with 4-methoxythiophenol providing the best reactivity when 2,6-lutidinium salts are used. A novel acridinium sensitizer provides enhanced reactivity within several of the more challenging reaction manifolds. This Article demonstrates how nucleophilic addition reactions mediated by photoredox catalysis can change the way electrophilic and homofugal precursors are constructed. Strong mineral acids usually add to alkenes such that hydrogen is added to the least substituted carbon — a pattern known as Markovnikov addition. Now, using photoredox catalysis in conjunction with a redox-active hydrogen atom donor, it has been shown that this pattern can be reversed to produce otherwise difficult to access products.
ISSN:1755-4330
1755-4349
DOI:10.1038/nchem.2000