- Regioselective Thermal [3+2]-Dipolar Cycloadditions of α-Diazoacetates with α-Sulfenyl/Sulfinyl/Sulfonyl-β-Chloroacrylamide Derivatives to Form Densely Functionalised Pyrazoles
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Highly regioselective synthetic methodology leading to densely functionalised C(3), C(4) and C(5) substituted pyrazoles 10a–q, 14a-i and 16a–g via thermal [3+2]-dipolar cycloaddition, of α-diazoacetates and α-thio-β-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 α-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.
- Flynn, Aaran J.,Ford, Alan,Khandavilli, U. B. Rao,Lawrence, Simon E.,Maguire, Anita R.
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supporting information
p. 5368 - 5384
(2019/06/24)
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- Trapping reactive metal-carbene complexes by a bis-pocket porphyrin: X-ray crystal structures of Ru=CHCO2et and trans-[Ru(CHR)(CO)] species and highly selective carbenoid transfer reaction
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What's in my pockets? By employing Suslick's bis-pocket porphyrin (ttppp), a reactive M=CHCO2Et complex and a trans-[M(CHR)(CO)] (M = Ru) complex have been structurally characterized by X-ray crystal analysis. The sterically encumbered ttppp ligand has a significant impact on both the diastereoselectivity and chemoselectivity in metalloporphyrin-catalyzed reactions of ethyl diazoacetate with conjugated aryl dienes.
- Deng, Qing-Hai,Chen, Jian,Huang, Jie-Sheng,Chui, Stephen Sin-Yin,Zhu, Nianyong,Li, Guang-Yu,Che, Chi-Ming
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supporting information; experimental part
p. 10707 - 10712
(2010/04/30)
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