(The) synthetic utility of 1-fluoro-2,4,6-trinitrobenzene and the reduction of cyclic ketones with lithium-di-isobuthl-n-butylaluminium hydride

Abstract

Macrolactonizations were carried out using 1-fluoro-2,4,6-trinitrobenzene and 4-dimethylaminopyridine as condensing agents for 12-hydroxydodecanoic acid and 6-hydroxyhexanoic acid. The isolated yields were rather low in contrast with high yields in the esterification. Several 2,4,6-trinitrophenyl esters were prepared by the reaction of equimolar amounts of carboxylic acid and 1-fluoro-2,4,6-trinitrobenzene in the presence of 0.5 equiv. of triethylamine. From the reaction of 2,4,6-trinitrobenzoate with several nucleophiles, acyl-oxygen and/or aryl-oxygen fission was observed. A possible mechanism of the esterification is suggested. The stereoselective reductions of a series of cyclohexanone derivatives with lithium diisobutyl-n-butylaluminium hydride, prepared from the reaction of diisobutylaluminium hydride and n-butyllithium, were performed in both toluene-n-hexane and tetrahydrofuran-n-hexane at $-78^\circ C$. Also, a comparison study of lithium trisec-butylboro-hydride and diisobutylaluminium hydride was carried out. For 3-methyl-, 4-methyl-, and 4-tert-butyl-cyclohexanones with little steric hindrance, no remarkable stereoselectivity was obtained. However, for sterically hindered compounds such as 2-methyl-, 2-tertbutyl-, and 3,3,5-trimethyl-cyclohexanone, lithium diisobutyl-n-butylaluminium hydride showed much higher stereoselectivity than that of diisobutylaluminium hydride. Furthermore, for highly sterically hindered 3,3,5-trimethylcyclohexanone and bicyclic ketones such as norcamphor and camphor, the stereoselectivity obtained with this reagent is comparable to that reported with L-selectride.