Protonation of anion intermediates in metal-ammonia reduction: 1,2- vs. 1,4-dihydro aromatic products

Abstract

The competition between 1,3-cyclohexadienes and 1,4-cyclohexadienes during metal-ammonia reduction has been examined. The former is usually regarded as a thermodynamic product and the latter as a kinetic product although, in actuality, little thermodynamic difference exists between these two isomers. 1,4-Cyclohexadiene was found to undergo proton abstraction with potassium or sodium amide in ammonia at -50/sup 0/C but not with lithium amide. Similarly, 1,3-cyclohexadiene reacts only with potassium amide and not with sodium or lithium amide. Consequences relating to the formation of conjugated and nonconjugated products during metal-ammonia reduction are discussed. The reaction of dihydronaphthalenes with various amides is also presented and again there is considerable variation in behavior. This has led to improved synthetic schemes for the selective production of 1,2-dihydro- and 1,4-dihydronaphthalenes as well as tetralins. Finally, protonation sites in pentadienyl type anions are considered. 4 tables.