Ar oute to 4-fluoropyridazines by a[ 2 + +1]/[3+ +2] cycloaddition sequence betweena na cetylenic derivative, ad ifluorocarbenes ource,a nd ad iazo compound is reported. This approach is highly modulara nd compatiblew ith ab road range of functional groups. The protocol does not require the isolation of any reactive intermediates and,t hus, allows for access to aw ide range of 4-fluoropyridazines in as ingle synthetics tep from simple alkynes. Furthermore, these fluorinated compounds can be easily diversified by nucleophilic aromatic substitution (S N Ar) to displace the fluoro group to give aw ider range of 3,4,6-trisubstituted pyridazines. As ar esult of increasing interest in functionalized pyridazines as wella sf luorinated derivatives, this efficient and concise approacht o4 -fluoropyridazines should be of value to medicinal chemists. Scheme1.(1) Synthesis of 5-fluoropyridazinesb ya[ 2 + +1]/[3+ +2] cycloaddition sequencew ith alkyl diazoacetates;(2) Synthesis of 4-fluoropyridazines by a[ 2 + +1]/[3+ +2] cycloaddition sequence with other diazo compounds (TMS = trimethylsilyl, TFDA = trimethylsilyl fluorosulfonyldifluoroacetate, Nu = nucleophile).Scheme2.Mechanism of the [2+ +1]/[3+ +2] cycloaddition sequence with (trimethylsilyl)diazomethane (E).
A ring contraction of 3-hydroxy-3-(trifluoromethyl)piperidines was achieved via an aziridinium intermediate. This contraction facilitates the synthesis of a series of 2-substituted 2-(trifluoromethyl)pyrrolidines incorporating a quaternary center at the C2 position.
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