On the deprotonation of 3,5-dichloropyridine using lithium bases: in situ infrared spectroscopic studies

International audienceDeprotonation of 3,5-dichloropyridine using LTMP and BuLi was monitored in real time by infrared spectroscopy. It appeared that the substrate was rapidly deprotonated. Transient structures between the substrate and the lithio derivative were detected. The absorbances recorded for the lithio derivative showed that the structures obtained using LTMP and BuLi were similar. When BuLi was used to deprotonate, a complete deuteration of the lithio derivative was noted upon quenching with D 2 O. The latter did not allow the quantification of the lithio derivative when LTMP was used, since only partial deuteration was observed

Deprotonation of Benzoxazole and Oxazole Using Lithium Magnesates

International audienceThe first deprotonations of oxazole and benzoxazole using lithium magnesates are described. The reactions occurred in tetrahydrofuran at room temperature using 1/3 equiv of lithium tributylmagnesate. As 2-lithiooxazole and 2-lithiobenzoxazole, lithium tri(2-oxazolyl)magnesate and lithium tri(2-benzoxazolyl)magnesate very rapidly and completely isomerized to the more stable 2-(isocyano)enolate and 2-(isocyano)phenolate type structures, respectively, a result shown by NMR analysis. The isolation of 2-substituted oxazoles and benzoxazoles in medium to good yields after electrophilic trapping was interpreted in two ways:  (1) the equilibration between the open and closed structures is faster than the trapping of the open isomers, and the closed isomers are more reactive than the open ones, or (2) the open isomers react with electrophiles in a intramolecular Passerini type reaction. The nonreactivity of the 2-(isocyano)enolate type structure toward anisaldehyde in the absence of lithium bromide makes the intramolecular Passerini type reaction more plausible