N-Heterocyclic carbene-catalyzed switchable reaction of 9-(trimethylsilyl)fluorene and aldehydes: chemoselective synthesis of dibenzofulvenes and fluorenyl alcohols

N-heterocyclic carbene-catalyzed synthesis of dibenzofulvenes and fluorenyl alcohols were developed. In the presence of 10 mol% NHC 1, 3-bis(2, 6-diisopropylphenyl) imidazol-2-ylidene and 4A molecular sieves, 9-(trimethylsilyl)fluorene undergoes olefination reaction with aldehydes to produce dibenzofulvenes in 43-99% yield. However, reducing the NHC loading to 1 mol% and with the addition of water, 9-(trimethylsilyl)fluorene selectively undergoes nucleophilic addition with aldehydes to afford fluorenyl alcohols in 40-95% yield.