Studies on new pathways to 1,3-Diyl and their application to triquinane synthesis

Abstract

Development of new pathways to 1,3-diyl for cycloaddition reaction to construct various polyquinane frameworks has been studied. The intramolecular [2+3] cycloaddition reaction of the 1,3-trimethylenemethane(TMM) diyl generated from the intramolecular cyclopropanation reaction of alkylidene carbene produced linearly, angularly fused triquinanes and tetaquinanes regio- and stereoselectively. This method provides a good synthetic strategy to construct polyquinane skeletons. However, it exhibits the several disadvantages such as 1,2-shift of alkylidene carbene and relatively low product yield. Therefore, alternative generation method of 1,3-diyl was needed to apply for the construction of polyquinane skeleton. A new efficient way to generate 1,3-trimethylenemethane(TMM) diyl was developed with allene and N-aziridinylimine or with allene and N-tosylhydrazone sodium salt. This synthetic strategy was successfully utilized in [2+3] cycloaddition reaction with olefin in high yield. The novel one pot sequential transformation of thermally labile pyrazole obtained through [2+3] cycloaddition reaction of diazoalkane with allene produced 1,3-trimethylenemethane(TMM) diyl and the generated diyl was trapped by olefin to form polyquinane framework. Total Synthesis of dl-pentalenene, angular triquinane natural product, was successful through 11 steps from (E)-2-methylhept-5-en-1-ol. Triquinane core structure was assembled by thermolysis of allenyl N-tosylhydrazone sodium salt.