Transition Metal-Free α-Csp³-H Methylenation of Ketones to Form C═C Bond Using Dimethyl Sulfoxide as Carbon Source

Abstract

A direct α-Csp-H methylenation of arylketones to form C═C bond using dimethyl sulfoxide as one-carbon source is achieved under transition metal-free reaction condition. Various aryl ketone derivatives react readily with DMSO, producing the α,β-unsaturated carbonyl compounds in yields of 42 to 90%. This method features a transition metal-free reaction condition, wide substrate scope and using DMSO as novel one-carbon source to form C═C bond, thus providing an efficient and expeditious approach to an important class of α,β-unsaturated carbonyl compounds. Based on the preliminary experiments, a plausible mechanism of this transformation is disclosed.

Photocatalytic C(sp3)−H Activation towards α‐methylenation of Ketones using MeOH as 1 C Source Steering Reagent

“…When, a mixture of acetophenone 1 a (1.0 mmol), K 2 CO 3 (1 mmol), PPh 3 (0.1 mmol) and MeOH (5 mL) was stirred for 8 h in the presence of g-C 3 N 4 (20 mg), and we were happy to isolate the desired product 2 a albeit in very low yield ( Table 1, entry 1). However, in the absence of either catalyst or additive or base, we could not isolate the any product 2 a (Table 1, entries [16][17][18]. After screening different catalysts, Cu@g-C 3 N 4 (15 wt%, 20 mg) not only improved the yield up to 97% but it increased the conversion rate also and reaction got completed only in 4 h ( (Table 1, entries 5 and 15).…”

“…The amount of catalyst was found 20 mg optimum; decreasing the catalyst loading from 20 to 15 mg, yield of the product 2 a was also decreased (Table 1, entries 5 and 14), while there was no change in yield on increasing the catalytic amount ( Table 1, entries 5 and 15). However, in the absence of either catalyst or additive or base, we could not isolate the any product 2 a (Table 1, entries [16][17][18]. Also, we performed the reaction under inert atmosphere.…”

“…[12][13][14][15] The strategy involves amethylenation of carbonyl compounds with formaldehyde [12] (Scheme 1a) and paraformaldehyde [13a] (Scheme 1b) as one-carbon source through Eschenmoser's salt promoted Mannich-type reaction followed by elimination. Accordingly, literature reports DMA, [16] DMF, [17] and DMSO [18] as alternative one carbon donating substrates for oxidative a-CÀH-methylenation (Scheme 1c-e). Accordingly, literature reports DMA, [16] DMF, [17] and DMSO [18] as alternative one carbon donating substrates for oxidative a-CÀH-methylenation (Scheme 1c-e).…”

“…[14,15] Thus, in spite of being highly reactive, [12,13] toxicity of HCHO has been the main limitation and led to search for new substrate scope for a-methylenation of ketones. However, poor reactivity of these alternatives 1 C-source [15][16][17][18] towards a-methylenation essentially demand oxidising agents and forcing refluxing temperature with slow conversion rate. However, poor reactivity of these alternatives 1 C-source [15][16][17][18] towards a-methylenation essentially demand oxidising agents and forcing refluxing temperature with slow conversion rate.…”

“…Accordingly, literature reports DMA, [16] DMF, [17] and DMSO [18] as alternative one carbon donating substrates for oxidative a-CÀH-methylenation (Scheme 1c-e). However, poor reactivity of these alternatives 1 C-source [15][16][17][18] towards a-methylenation essentially demand oxidising agents and forcing refluxing temperature with slow conversion rate. [15][16][17][18] Thus, search for efficient and mild one-carbon source for improved a-methylenation of ketones is still crucial and highly demanding target in organic synthesis.…”