Cobalt(II)porphyrin-Mediated Selective Synthesis of 1,5-Diketones via an Interrupted-Borrowing Hydrogen Strategy Using Methanol as a C1 Source

Abstract

A novel cobalt­(II)­porphyrin-mediated acceptorless dehydrogenation of methanol is reported for the first time. This methodology has been applied for the coupling of a variety of ketones with methanol to produce 1,5-diketones along with H2 and H2O as the environment friendly byproducts. This paradigm was also demonstrated for a one-pot synthesis of substituted pyridines using a sequential addition protocol where the 1,5-diketones were generated in situ. From many experiments including those involving deuterium labeling, it is proposed that protonated cobalt­(II)­porphyrin methoxide complex acts as an intermediate to generate formaldehyde along with a metal hydride.

Palladium-Mediated Tandem Isomerization–Methylenation of Allyl Alcohols: One-Pot Synthesis of 1,5-Diketones

“…Based on the above findings and recent reports, 14,20 we propose the following mechanism (Scheme 4). Allylic alcohol A is deprotonated in the presence of a base to produce the species B, which undergoes β-hydride elimination leading to species C. Species C undergoes 1,4-hydride addition, resulting in the formation of enolic species D, which either results in the enol E or can further tautomerize to yield ketone F. Formaldehyde produced from methanol in the presence of palladium adds to the ketone product F resulting in αmethylenated species G through aldol condensation.…”

“…Based on the above findings and recent reports, , we propose the following mechanism (Scheme ). Allylic alcohol A is deprotonated in the presence of a base to produce the species B , which undergoes β-hydride elimination leading to species C .…”

“…Unless mentioned, all reactions were carried out under aerobic condition and at a 0.5 mmol scale. Diastereomeric ratios were determined from 1 H NMR and identified as per the recent report …”

Using Methanol as a Formaldehyde Surrogate for Sustainable Synthesis of N‐Heterocycles via Manganese‐Catalyzed Dehydrogenative Cyclization

“…[ 12e,13 ] In addition, the methylenation of aryl ketones and methyl acetate has been realized using methanol as a formaldehyde surrogate via catalytic dehydrogenation with the assistance of oxygen. [ 14 ]…”

Palladium‐Catalyzed Synthesis of α‐Methyl Ketones from Allylic Alcohols and Methanol

“…Recently, we have reported the synthesis of monomethylated amines, ketones and 1,5‐diketones using methanol as a reagent [11d,14] . As part of our continuing efforts to use methanol as a reagent, here, we report a one‐pot conversion of secondary allylic alcohols (both 1,3‐diaryl propenols and 1‐aryl propenols) to α‐methyl ketones via isomerisation‐methylation reactions using methanol as a C1 source and commercially available palladium acetate as a catalyst (Scheme 1d) to overcome the limitations of the above reports.…”