Abstract
The Baeyer-Villiger reaction is used extensively in organic chemistry. Sila- and bora-variants have also been documented widely, with these processes underpinning, for example, the Fleming-Tamao oxidation and hydroborative alkene hydration, respectively. By contrast, the development of thia-Baeyer-Villiger reactions involving sulfoxides has long been considered unlikely because competitive oxidation to the sulfone occurs exclusively. Here, we disclose a photoinduced thia-Baeyer-Villiger-type oxidations; specifically, we find that exposure of dibenzothiophene (DBT) derivatives to an iron porphyrin catalyst under Ultraviolet irradiation in the presence of t-BuOOH generates sulfinic esters in up to 87% yield. The produced sulfinic esters are transformed to a variety of biphenyl substrates including biphenyl sulfoxides, sulfones and sulfonamides in 1-2 steps. These results provide a mild process for the selective functionalization of sulfur compounds, and offer a biomimetic approach to convert DBT into 2-hydroxybiphenyl under controllable stepwise pathway. Based upon experimental evidences and DFT calculation, a mechanism is proposed.
Highlights
The Baeyer-Villiger reaction is used extensively in organic chemistry
During studies on the biomimetic oxidation of DBT 10a catalyzed by the iron porphyrin complex [TCPPFe]Cl (5,10,15,20-Tetrakis (2-chlorophenyl)porphyrinato) iron (III) chloride)[20,21,22,23,24,25,26,27,28,29,30,31,32], we observed that the initial oxidation product, sulfoxide DBTO 11a, underwent facile conversion to the corresponding sulfone DBTO2 12a20
Spectroscopic analysis indicated that this product was nonsymmetrical and it was assigned as sulfinic ester (BPS, 13a) by comparison to data reported by Crich[33], who prepared this compound via a different synthetic route
Summary
The Baeyer-Villiger reaction is used extensively in organic chemistry. Sila- and bora-variants have been documented widely, with these processes underpinning, for example, the Fleming-Tamao oxidation and hydroborative alkene hydration, respectively. The produced sulfinic esters are transformed to a variety of biphenyl substrates including biphenyl sulfoxides, sulfones and sulfonamides in 1-2 steps These results provide a mild process for the selective functionalization of sulfur compounds, and offer a biomimetic approach to convert DBT into 2-hydroxybiphenyl under controllable stepwise pathway. 3 with basic hydrogen peroxide affords the corresponding borate esters 4 via a bora-analog of the Baeyer–Villiger rearrangement; subsequent hydrolysis generates the corresponding alcohols This process is the final step of the alkenes hydroboration reaction, which effects the net anti-Markovnikov hydration of alkenes (Fig. 1b)[5,6,7]. In stark contrast, related oxygen atom insertion processes involving carbon sulfoxide bonds, to generate the corresponding sulfinic esters 8, have not been reported, and, have long been considered a hopeless endeavor. Even if such a thia-Baeyer–Villliger reaction could be achieved, it has been shown in certain cases that sulfinic esters 8 will rearrange to sulfones 9, which highlights a further challenge that must be overcome[12]
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