Synthetic studies towards the mannolides: Construction of the bowl-shaped B/C/D ring system

The bowl-shaped tricyclo[6.3.1.0(4)(,1)(2)]dodecane moiety is the core feature of cephalotane-type diterpenoids. As part of our efforts directed towards a total synthesis of mannolide B, the bowl-shaped tricyclo [6.3.1.0(4)(,1)(2)]dodecane skeleton, a common intermediate of cephalotane-type diterpenoids bearing up to five contiguous stereocenters including two quaternary carbon centers had been constructed. The synthetic strategy was enabled by an efficient application of oxidative dearomatization/intramolecular DielsAlder reaction to access highly functionalized building block with the tricyclo[5.2.2.0(2,6)]undecane unit from commercially available materials. The key feature was firstly used the cyclic olefins with secondary alcohol as dienophile for the intramolecular inverse electron demand Diels-Alder reaction. Further synthetic studies led to construct ring D by a regioselective Aldol reaction. (C) 2020 Elsevier Ltd. All rights reserved.