RESUMO
Reversing the polarity in molecules is a versatile tool for expanding the boundaries of structural space. Despite a manifold of different umpolung methods available today, overcoming the inherent reactivity still remains a constant challenge in organic chemistry. The oxidative α-functionalization of ketones by external nucleophiles constitute such an example. Herein, we present a hypervalent F-iodane mediated umpolung of pyridyl ketones triggered by Lewis base/Lewis acid noncovalent interactions. A wide variety of external nucleophiles are introduced with high regioselectivity applying this substrate-directing concept.
RESUMO
Our recent studies of the diastereo- and enantioselective formation of strained alkylidenecycloalkanes drove us to more-thoroughly investigate the formation of four-membered rings for which only few efficient methods are described. We first developed a strategy to diversify the saturated part of the four-membered ring and applied it to a highly diastereoselective synthesis of more-elaborate alkylidenecyclobutanes, which completed our precedent studies. In parallel, cyclobutene structures were built employing simple organometallic methods and further functionalized to give a diverse range of new substitution patterns, which consequently enriched the pool of cyclobutene-based building blocks.
RESUMO
Enantioenriched alkylidenecyclobutanes possessing a quaternary stereogenic center, usually difficult to access, have been synthesized by combining a double boron-homologation and an allylboration through a highly efficient and diastereoselective one-pot process. Starting from commercially available substrates, this protocol represents a simple way of accessing chiral unsaturated four-membered ring systems with excellent stereoisomeric ratios.