Scheme 2.
Syntheses of 4-Substituted Butyric Acid Pentyl Esters (9, 11, and 12)a
a Reagents: (a) pentanol, DMAP, DMF, rt; (b) BH3–THF complex, THF, −10 °C, N2; (c) 3-chlorophenyl isocyanate, triethylamine, DMF; (d) 3-chlorophenylacetic acid, isobutyl chloroformate, triethylamine, DMF, rt; (e) 4-nitrophenyl chloroformate, triethylamine, DMF, rt; (f) 3-chlorophenol, potassium carbonate, acetonitrile, rt.