(–)-Bipolarolide D
A rare example of a [6 + 2]-cycloaddition
I wrote the other month about my love of cycloadditions (cycloaddiction, if you will), and we’ll see one take centre stage again today. But before we get into that, I need to get something off my chest about the way we name these transformations. Take the most famous, textbook example – the Diels–Alder reaction. In its simplest form, a diene reacts with an alkene to form a cyclohexene ring. In the language of the Nobel-prize-winning system laid down by RB Woodward and Roald Hoffman, that’s a [4+2]-cycloaddition because of the number of electrons in the reacting partners – four in the diene and two in the alkene.