Abstract
An introduction to hops is presented which includes an account of the morphology of the hop plant (Humulus lupulus L.), and a brief history of the use of hops in the brewing of beer. The chemistry of the humulinic acids is outlined from the isolation of humulinic acid A to that of humulinic acids C md D. To achieve a rational synthesis of humulinic acid C, which was the main object of the study, it appeared that it would first be necessary to synthesise the tetrahydrofuran, ethyl 2,2-dimethyl-5-ethoxycarbonyl-5-tetrahydro-furylacetate. Two approaches were made to the synthesis of this vital intermediate. One involved incorporation of the 5,5-diester group into a reaction scheme before the tetrahydrofuran ring was formed, whilst the other, was to prepare a tetrahydrofuran with the 5-position suitably disubstituted so that a further reaction would then afford the required intermediate. The former approach was unsuccessful while the latter was partially successful in that a number of 5,5-disubstituted 2,2-dimethyltetrahydrofurans were prepared. Attempts to convert 2,2-dimethyl-5-ethoxymethyl-5-ethoxy-ethyltetrahydrofuran to the required diester tetrahydrofuran were unsuccessful. Humulinic acid C was prepared by degradation of humulinic acid A which had been obtained from hop-oil humulone. Degradation of humulinic acid C' afforded ethyl 2,2-dimethyl-5-ethoxycarbonyltetrahydrofurylacetate which was then degraded two steps further to yield 2,2-dimethyl-5-ethoxyethyl-5-ethoxymethyltetrahydrofuran (which had also been prepared by a synthetic route). The p.m.r. spectra of the two compounds were the same confirming that they were identical in structure. Further suggestions for the synthesis of the diester tetrahydrofuran are also made.