Phosphaborenes: accessible reagents for C-C/P-B isosteres

Formal exchange of C=C units with isoelectronic B=N or B=P units can provide access to molecules with unique electronic or chemical properties. Here, we report the simple solution-phase generation of highly reactive phosphaborenes, RP=BR, and demonstrate their use for the introduction of P=B units into organic systems. A P-B containing cyclobutene isostere can be ring opened to access unique 1,4-bora-phospha-butadiene systems with conjugated main-group multiple bonds.