Addition of Organolithium Reagents to Corannulene and Conformational Preferences in 1-Alkyl-1,2-dihydrocorannulenes

Addition of organolithium reagents to corannulene (1) produces 1-R-1,2-dihydrocorannulenes (2), which can be easily converted to 1-R-corannulenes (3). Molecular mechanics (MM) calculations predict a slight pseudoequatorial preference for the small substituents in both exo and endo arrangements of 2, whereas bulky substituents are expected to favor strongly the exo-pseudoaxial location. X-ray diffraction studies show the exo-pseudoaxial conformation in the solid state for both i-Pr and t-Bu-2. In solution, a gradual increase in the contribution of pseudoequatorial conformations with decreasing size of the substituent is demonstrated by analysis of the ³J H−H coupling constants within the reduced ring.