Unstable compounds. Synthesis, structure, and experimental and computational carbocation chemistry of 2-cumyladamantan-2-ol and its chromium .eta.6-Cr(CO)3 complex

Reactivity of (η6-Arene)tricarbonylchromium Complexes toward Additions of Anions, Cations, and Radicals

“…In the cyclic cases, shifting the carbon to the metal center also involves release of ring strain, increasing the exothermicity of these rearrangements. Direct interaction of the chromium with distant cations, as in the formation of 34c , suggests that chromium complexation of arenes could influence solvolysis reactions beyond the presently known α- and β-positions, 1b,, to the γ-position and perhaps beyond. Indeed, the computational comparison between pseudo four-membered ring 39c and pseudo five-membered ring 40c indicates that the larger ring is actually favored (eq 7).…”

“…Computations strongly favored chromium−carbon interactions in the cationic intermediates rather than σ−π-type interactions . A recent solvolysis study on an adamantyl complex found no interaction of the chromium or the arene and a β-cation, though this system was sterically congested …”

Neighboring Group Participation by Chromium in Substitution Reactions of (η6-Arene)tricarbonylchromium Complexes

“…25 However, here we begin to address the question of whether participation by a metal center in a distal ligand-centered reaction can impart changes in the rate, regiochemistry, and stereochemistry of the reaction. We contend that just as benzylic positions exhibit cationic stabilization via direct coordination to chromium (I), so can cations at the β-and γ-positions (II and III), barring strong steric demands or cation stabilization, 26 and that this interaction can be utilized for formation of carbon-carbon bonds and control of stereochemistry. Further, this should extend to other metal systems.…”

Ionic and Organometallic‐Catalyzed Organosilane Reductions

“…126 These undesirable side reactions may be avoided or reduced by running the reaction at −78 • . 140 Sulfuric acid may cause undesirable oxidations to occur. 134 On balance, the most commonly chosen set of conditions for the reduction of alcohols is triethylsilane and trifluoroacetic acid (Et 3 SiH/TFA) in dichloromethane solution.…”

“…155 The high yield of a single very strained hydrocarbon product in each reaction is quite surprising in view of the very complex interconversions of carbocations known to take place from the alcohol precursors. 140,151,152,156 The remarkable chemoselectivity of this reductive technique is demonstrated by the conversion of the functionally rich compound 13 into 14 in 86% yield upon treatment with Et 3 SiH/TFA at room temperature for two hours (Eq. 17) This reagent combination reduces a tertiary alcohol in the presence of a quinone moiety (Eq.…”