Synthesis of mono- and difluoronaphthoic acids.
Aryl carboxamides are useful structural units found in several biologically active compounds. Unlike their benzoic acid counterparts, fluorinated versions of naphthoic acids are relatively unknown. In connection with a recent project, we needed viable syntheses of several mono- and difluorinated naphthoic acids. Herein we describe the synthesis of 5-, 6-, 7-, and 8-fluoro-1-naphthalenecarboxylic acids and 5,7-, 5,8-, 6,7-, and 4,5-difluoro-1-naphthalenecarboxylic acids. The 5-fluoro derivative 1was obtained from the corresponding 5-bromo compound via electrophilic fluorination of the lithio-intermediate. The rest of the monofluoro (2, 3, and 4) and the difluoro acids (5, 6, and 7) were prepared by a new, general route which entailed the elaboration of commercial fluorinated phenylacetic acids to 2-(fluoroaryl)glutaric acids with differential ester groups; selective hydrolysis to a mono acid, intramolecular Friedel-Crafts cyclization, and aromatization furnished the target structures. An alternative process to assemble a naphthalene skeleton is also presented for the difluoro acids 5 and 6. Finally, 4,5-difluoro-1-naphthalenecarboxylic acid (8) was prepared expeditiously from 1,8-diaminonaphthalene by adapting classical reactions.
Tagat
Jayaram R
JR
Chemical Research, Schering-Plough Research Institute, 2015, Galloping Hill Road, K-15-2B-2800, Kenilworth, New Jersey 07033-0539, USA. jarayam.tagat@spcorp.com
McCombie
Stuart W
SW
Nazareno
Dennis V
DV
Boyle
Craig D
CD
Kozlowski
Joseph A
JA
Chackalamannil
Samuel
S
Josien
Hubert
H
Wang
Yuguang
Y
Zhou
Guowei
G