Catalytic Arylboration of Spirocyclic Cyclobutenes: Rapid Access to Highly Substituted Spiro[3.n]alkanes

A method
to achieve the synthesis of highly substituted spirocyclic
cyclobutanes is disclosed. The reaction involves the catalytic arylboration
of cyclobutenes. Depending on the substitution pattern of the cyclobutene,
either a Cu/Pd- or a Ni-catalyzed reaction was utilized. In the case
of the Cu/Pd-catalyzed reactions, the identification of a Cu-complex
for arylboration was crucial to observe high selectivity. The synthetic
utility of the products is demonstrated, and the mechanistic details
are discussed.