Synthesis of anti‐Markovnikov Alcohols via Epoxidation and Hydrogenation of Styrenes using Photocatalytically Generated Redox Equivalents

Abstract

We report an efficient method for a formal anti-Markovnikov addition of water to styrenes through photocatalytic generation of redox equivalents, using a gold-doped titanium dioxide (Au/ TiO 2 ) semiconductor as photocatalyst. Under irradiation with UVÀ A light, the photocatalytic activity of Au/TiO 2 generates in situ under aerobic conditions hydrogen peroxide (H 2 O 2 ) and under anaerobic conditions dihydrogen (H 2 ). In the presence of oxygen and a Ru catalyst, the epoxidation of different styrene derivatives is achieved. Subsequently, regioselective reductive Pd-catalyzed epoxide opening in the absence of oxygen gives the corresponding 2-phenylethanol derivatives.

Catalytic Hydrogenation of Epoxides to Alcohols

“…[37] Recently, König and coworkers achieved epoxidation of styrene derivatives and subsequent reduction to primary alcohols by a photocatalyst (Scheme 18b). [38] Various styrene oxides were tested using Au/ TiO 2 photocatalyst, which afforded the corresponding 2-phenyl ethanol derivatives in moderate to good yields. Werner group disclosed cobalt pincer catalyzed anti-Markovnikov ring-opening of epoxides via transfer hydrogenation using ammonia borane (NH 3 BH 3 ) as the hydrogen source (Scheme 18c).…”

“…In 2003, Yu and coworkers described Pd nanoparticles microencapsulated in urea as an efficient and recyclable catalyst for the hydrogenolysis of epoxides using HCOOH/Et 3 N as hydrogen donor (Scheme 18a) [37] . Recently, König and coworkers achieved epoxidation of styrene derivatives and subsequent reduction to primary alcohols by a photocatalyst (Scheme 18b) [38] . Various styrene oxides were tested using Au/TiO 2 photocatalyst, which afforded the corresponding 2‐phenyl ethanol derivatives in moderate to good yields.…”

Gold photocatalysis in sustainable hydrogen peroxide generation

“…Although this review presents discussion exclusively about photocatalytic H 2 O 2 production, it is also insightful and beneficial for other photocatalytic reactions that utilize H 2 O 2 as an oxidant or intermediate, for example Fenton reaction [84,85], oxidation of alcohols, or amines [71,86], epoxidation [87], water oxidation [88], fuel cells [89], environmental remediation [90] and biological processes [3,4]. For example, photocatalytic water splitting that generate H 2 and O 2 gases requires a membrane separation to collect pure H 2 .…”

Catalytic Conversion of Styrene to Benzaldehyde over S-Scheme Photocatalysts by Singlet Oxygen

“…In addition, typical inorganic semiconductors such as TiO 2 were employed in photocatalytic styrene cleavage. 14 The authors proposed an anti-Markovnikov reaction mechanism based on the variation in products at different reaction atmospheres. Although excellent performance was acquired in these pioneering studies and plausible photocatalytic mechanisms were proposed, these mechanisms were not validated.…”