Steric Influence on Reactions of Benzyl Potassium Species with CO

Reactions of benzyl potassium species with CO are shown to proceed via transient carbene‐like intermediates that can undergo either dimerization or further CO propagation. In a sterically unhindered case, formal dimerization of the carbene is the dominant reaction pathway, as evidenced by the isolation of ((Ph(3)SiO)(PhCH(2))C)(2) 2 and PhCH(2)C(O)CH(OH)CH(2)Ph 3. Reactions with increasingly sterically encumbered reagents show competitive reaction pathways involving intermolecular dimerization leading to species analogous to 2 and 3 and those containing newly‐formed five‐membered rings tBu(2)C(6)H(2)(C(OSiR(3))C(OSiR(3))CH(2)) (R=Me 6, Ph 7). Even further encumbered reagents proceed to either dimerize or react with additional CO to give a ketene‐like intermediates, thus affording a 7‐membered tropolone derivative 14 or the dione (3,5‐tBu(2)C(6)H(3))(3)C(6)H(2)CH(2)C(O))(2) 15.