David H. Brown Ripin
Pfizer
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Featured researches published by David H. Brown Ripin.
Organic and Biomolecular Chemistry | 2005
Timothy Norris; Roberto Colon-Cruz; David H. Brown Ripin
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.
Tetrahedron Letters | 2000
David H. Brown Ripin; Weiling Cai; Steven J. Brenek
Abstract A new procedure for the oxidation of carbon–boron bonds to the corresponding alcohol with Oxone ® is described.
Tetrahedron Letters | 2001
Joseph Dupont; Raymond J. Bemish; Keith E. McCarthy; Emily R. Payne; Ernest B. Pollard; David H. Brown Ripin; Brian C. Vanderplas; Richard M. Watrous
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.
Chemical Reviews | 2006
Stephane Caron; Robert W. Dugger; Sally Gut Ruggeri; John A. Ragan; David H. Brown Ripin
Organic Process Research & Development | 2005
Robert W. Dugger; and John A. Ragan; David H. Brown Ripin
Journal of Medicinal Chemistry | 2005
Kim F. McClure; Yuriy A. Abramov; Ellen R. Laird; John T. Barberia; Weiling Cai; Thomas J. Carty; Santo R. Cortina; Dennis E. Danley; Alan J. Dipesa; Kathleen M. Donahue; Mark A. Dombroski; Nancy C. Elliott; Christopher A. Gabel; Seungil Han; Thomas R. Hynes; Peter K. LeMotte; Mahmoud N. Mansour; Eric S. Marr; Michael A. Letavic; Jayvardhan Pandit; David H. Brown Ripin; Francis J. Sweeney; Douglas H. Tan; Yong Tao
Organic Process Research & Development | 2005
David H. Brown Ripin; Dennis E. Bourassa; Thomas A. Brandt; Michael J. Castaldi; Heather N. Frost; Joel M. Hawkins; Phillip J. Johnson; Stephen S. Massett; Karin Neumann; James Phillips; Jeffery W. Raggon; Peter Robert Rose; Jennifer L. Rutherford; Barbara J. Sitter; A. Morgan Stewart; Michael G. Vetelino; Lulin Wei
Organic Process Research & Development | 2003
David H. Brown Ripin; Stefan Abele; Weiling Cai; Todd Andrew Blumenkopf; Jeffrey M. Casavant; Jonathan L. Doty; Mark Edward Flanagan; Christian Koecher; Klaus Laue; Keith E. McCarthy; Cliff Meltz; Mike Munchhoff; Kees Pouwer; Bharat Shah; Jianmin Sun; John Teixeira; Ton Vries; David A. Whipple; Glenn E Wilcox
Synlett | 2003
David H. Brown Ripin; Michael G. Vetelino
Archive | 2003
David H. Brown Ripin