Spiro[4H-chromene-4,5′-isoxazolines] and related compounds: Synthesis and reactivities

Abstract

Reactions of chromones with methyl ketoximes in the presence of lithium diisopropylamide follow the nucleophilic 1,2 addition mechanism to give spiro[4H chromene 4,5´ isoxazolines] in good yields. The isoxazoline ring in spiro[4H chromene 4,5´ isoxazolines] undergoes open ing under the action of conc. H 2 SO 4 , yielding α,β unsaturated oximes. Their nitrosation and bromination lead to the corresponding spiroisoxazolines, while the Beckmann rearrangement, to α,β unsaturated amides. The latter are also formed directly from spiro[4H chromene 4,5´ isoxazolines] under the action of PCl 5 . N Substituted acetophenone hydrazones in the pres ence of lithium diisopropylamide react at the C(4) atom of 2 trifluoromethylchromone, while acetophenone anil under the same conditions, at the C(2) atom.

Selective Incorporation of Fluorine in Pyrazoles

“…[80] Bonacorso and fellow researchers devised a one-pot process in which the trifluoromethyl-substituted α,β-unsaturated ketone 117 underwent dual condensation with aminoguanidine hydrogen carbonate and was subsequently dehydrated to give [5-trifluoromethylpyrazol-1-yl]-3-(trifluoromethyl)pyr-imidines 118 in yields ranging from 28-65 %. [58] Mykailiuk's team used α,β-unsaturated ketone 121 to form the (trifluoromethyl)pyrazoles 123a and 123b in moderate to poor yields of 56 % and 15 % respectively. [58] Mykailiuk's team used α,β-unsaturated ketone 121 to form the (trifluoromethyl)pyrazoles 123a and 123b in moderate to poor yields of 56 % and 15 % respectively.…”