Peer-Reviewed Journal Details
Mandatory Fields
Flynn, Aaran J.,Ford, Alan,Khandavilli, U. B. Rao,Lawrence, Simon E.,Maguire, Anita R.
2019
Unknown
European Journal of Organic Chemistry
Regioselective Thermal [3+2]-Dipolar Cycloadditions of a-Diazoacetates with a-Sulfenyl/Sulfinyl/Sulfonyl--Chloroacrylamide Derivatives to Form Densely Functionalised Pyrazoles
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[3+2]‐Dipolar cycloaddition Sulfonyl migration Pyrazole Tautomers α‐Thio‐β‐chloroacrylamide
Highly regioselective synthetic methodology leading to densely functionalised C(3), C(4) and C(5) substituted pyrazoles 10aq, 14a-i and 16ag via thermal [3+2]-dipolar cycloaddition, of a-diazoacetates and a-thio--chloroacrylamides, at the sulfide, sulfoxide and sulfone levels of oxidation, is described. This method allows access to C(4)-sulfenyl or sulfonyl pyrazoles, through migration of the sulfur substituent at the sulfide and sulfone oxidation levels, while elimination of the sulfinyl group leading to 3,5-disubstituted pyrazoles, is observed. While the sulfide migration is readily rationalised, the carbon to carbon 1,2-sulfonyl migration is unprecedented and mechanistically intriguing. The synthetically versatile generation of densely functionalised pyrazoles containing substituents amenable to further modification offers advantages over alternative synthetic routes. Isolation of the N-alkylated pyrazoles 11a and 12a as by-products from the cycloaddition through further reaction of the pyrazoles 10 with excess a-diazoacetate, proved useful in rationalising the tautomeric behaviour evident in the NMR spectra of the pyrazoles, with the position of tautomeric equilibrium influenced by solvent and substituents.
1434-193X
https://onlinelibrary.wiley.com/doi/abs/10.1002/ejoc.201900494
10.1002/ejoc.201900494
Grant Details
Science Foundation Ireland
12/RC/2275; 15/RI/3221