Abstract
A mild ruthenium(II)-catalyzed homocoupling of α-carbonyl sulfoxonium ylides was developed and the detailed mechanism was understood based on DFT calculations in the current report. The catalytic system utilizes the α-carbonyl sulfoxonium ylide as both the directing group for ortho-sp2 C-H activation and the acylmethylating reagent for C-C coupling. Various substituents are compatible in the transformation and a variety of isocoumarin derivatives were synthesized at room temperature without any protection. The theoretical results disclosed that the full catalytic cycle contains eight elementary steps, and in all the cationic Ru(II) monomer is involved as the catalytic active species. The acid additive is responsible for protonation of the ylide carbon prior to the intramolecular nucleophilic addition and C-C bond cleavage. Interestingly, the intermediacy of free acylmethylation intermediate or its enol isomer is not necessary for the transformation.
Highlights
Under transition metal catalysis, the sulfoxonium ylides have found wide applications in synthetic chemistry (Li et al, 1997)
As a continuation of our interest in synthetic and mechanistic study of transition metal-catalyzed C-H activations (Xu et al, SCHEME 1 | Applications of α-carbonyl sulfoxonium ylides under transition metal catalysis. 2012; Gao et al, 2015; Guo and Xia, 2015; Guo et al, 2015; Zhou et al, 2015; Chen et al, 2016; Wang et al, 2017, 2018; Pan et al, 2018; Xie et al, 2018a; Xie H. et al, 2018), in the current report we present a combined experimental and theoretical study of ruthenium(II)-catalyzed homocoupling of α-carbonyl sulfoxonium ylides, affording a variety of isocoumarin derivatives under mild conditions (Scheme 1C). (Liang et al, 2018; Xu et al, 2018; Huang et al, 2019; Zhou et al, 2019; Wen et al, 2020; Zhu et al, 2020)
We initiated the investigation by optimizing the reaction conditions for the homocoupling of α-carbonyl sulfoxonium ylide 1a to form isocoumarin 2a (Table 1) under Ru(II) catalysis
Summary
The sulfoxonium ylides have found wide applications in synthetic chemistry (Li et al, 1997). These species could be used as efficient carbene precursors by elimination of dimethyl sulfoxide (DMSO) by activation of the ylide C-S bond with metal (Bayer and Vaitla, 2018; Cheng et al, 2018) This strategy has recently found important applications in transition metal-catalyzed C-H activation reactions (Scheme 1) (Gulias and Mascarenas, 2016; Wang et al, 2016; Sambiagio et al, 2018), as sulfoxonium ylides possess the advantages of easy availability of starting materials and safe operation in reactions compared with the alternative approach with diazo precursors (Davies and Manning, 2008; Xia et al, 2017; Clare et al, 2019; Wen et al, 2019; Zhou et al, 2020). Tandem intramolecular annulations of the in-situ generated acylmethylation products
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
