David H. Brown Ripin

New hydroxy-pyrazoline intermediates, subtle regio-selectivity and relative reaction rate variations observed during acid catalyzed and neutral pyrazole cyclization.

Arylhydrazines 4 and 1,3-dicarbonyl compounds 5 react to form pyrazoles by loss of water via hydrazone isomer pairs 6 and 7 which give rise to two possible regio-isomers. Occasionally, 3-hydroxy-3,4-dihydropyrazoles or hydroxy-pyrazolines 9 and 9 are observed as stable isolatable intermediates that can be fully characterized prior to loss of the second molecule of water that gives rise to pyrazoles 10 and 11. Fully characterized examples of intermediates of type 8 and 9 are relatively rare. We studied the reaction series where R = CH3, CHF2 and CF3 and Ar = Ph and 5-methanesulfonylpyridin-2-yl, (Scheme 2), and observed differences in properties between kinetic behavior and regio-isomerism depending on the degree of electron-withdrawing capability of the R and Ar substituents. The reaction conditions that caused cyclization to pyrazoles varied from direct condensation of the hydrazine and 1,3-dicarbonyl compounds, to reactions requiring catalytic quantities of sulfuric acid to sulfuric acid in excess. Unexpected regio-selectivity was observed in the case of R = CF3 that depended upon the reaction conditions.

A safe, scaleable method for the oxidation of carbon–boron bonds with oxone®

Abstract A new procedure for the oxidation of carbon–boron bonds to the corresponding alcohol with Oxone ® is described.

Oxidation of carbamate-protected alkylhydrazines to the corresponding hydrazones under Swern conditions

Abstract Carbamate protected alkylhydrazines have been found to oxidize cleanly to the corresponding hydrazone under Swern conditions. The reaction works on hydrazines with primary, secondary, and branched alkyl groups.