Acceptorless Dehydrogenation of Primary and Secondary Alcohols Catalysed by Phosphine-free C, C Chelated Ir (III) NHC Complexes

Herein, an efficient, atom-economic, environmentally benign catalytic protocol has been developed for synthesising ketones and aldehydes by acceptorless dehydrogenation of alcohols. The protocol employs C, C chelated Ir (III) NHC complexes to promote acceptorless dehydrogenation of both secondary and primary alcohols. Notably, oxidation of primary alcohol selectively yields the corresponding aldehyde where forming ester byproducts is possible. Using C, C chelated Ir (III) NHC complexes (0.1 mol%), and a catalytic amount of base tBuONa (5 mol%), several aliphatic and aromatic aldehydes and ketones including more challenging carbonyl compounds bearing heterocyclic rings were obtained in moderate to high yields. Moreover, the protocol is also efficient for synthesising industrially important molecules like heliotropin and 3,4,5-trimethoxy acetophenone in moderate yields. Remarkably, the catalytic system allows the straightforward synthesis of the potentially bio-active compound cholest-4-en-3-one through acceptorless dehydrogenation followed by double bond isomerisation under the reaction conditions. Low catalyst loading, mild reaction conditions, high selectivity, short reaction time, and broad-substrate scopes are a few interesting characteristics of the catalytic protocol described herein. The study describes an eco-friendly catalytic method for the synthesis of aldehydes and ketones through the acceptorless dehydrogenation of primary and secondary alcohols, employing phosphine-free C, C chelated Ir (III) NHC complexes as catalysts in the presence of tBuONa base in toluene at 80 degrees C. Notably, this method demonstrates high efficiency in producing industrially relevant molecules such as heliotropin, 3,4,5-tri methoxy acetophenone, and cholest-4-en-3-one. image