Synthesis of Functionalized Cyclic Boronates

Deprotonation of
a simple borylated allylic sulfone and subsequent
alkylation with certain unsaturated electrophiles provide substrates
that are easily converted into functionalized alkenyl boronates with
ring sizes from five- to seven-membered. A Chan–Lam reaction
on one such substrate afforded an alkoxyallylic sulfone that was readily
converted via a (4 + 3)-cycloaddition to a polycycle possessing the
ABC ring substructure of ingenol.