33885-01-7Relevant articles and documents
The Grignard reagent formation reaction of 2-chloro-1,1,1-triphenylethane revisited
Bickelhaupt, Friedrich,Newcomb, Martin,DeZutter, Christopher B.,De Boer, Henk J. R.
experimental part, p. 6225 - 6231 (2009/05/31)
The reaction of 2-chloro-1,1,1-triphenylethane (1) with magnesium in THF has been reinvestigated. The reaction produced a dark-red solution and after deuterolysis with D2O, 1,1,1-triphenylethane (2; 16%), 2-D-1,1,1-triphenylethane (3; 52%) and 1,1,2-triphenylethene (4; 26%) were isolated. Rate constants for phenyl migration in the 2,2,2-triphenylethyl radical were measured directly between 23°C and 55°C; the reaction is described by logk = 11.2 - 7.5/2.3 RT [kcal/mol] and the rate constant for rearrangement at 20°C is 4.0 × 105 s-1. The combined results support the intermediate formation of radicals in the reaction of chloride 1 with magnesium. The red colour of the reaction mixture, however, indicates the formation of a carbanionic species, which has not yet been identified. The diffusion model for Grignard formation reactions of Garst et al. is in line with the product distribution. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.
Carbon-Skeletal Anionic Rearrangements and the ?-Orbital Overlap Constraint: The Question of Nucleophilic Attack versus Electron Transfer
Eisch, John J.,Kovacs, Csaba A.,Chobe, Prabohd
, p. 1275 - 1284 (2007/10/02)
In order to evaluate the geometrical requirements and the actual electronic nature of apparent anionic rearrangements of metalated aromatic hydrocarbons, amines, and ethers, cyclic structural types of such anions were generated as lithium salts by proton abstraction from C-H bonds by RLi or by C-Cl bond cleavage by Li.The cyclic systems examined were anions of 9,9-dimethyl-, 9-methyl-9-benzyl-, and 9-benzyl-9-phenylfluorenes; 9-methyl-9-phenyl-, 9,9-diphenyl-, and 9,9-(2,2'-biphenylene)-9,10-dihydrophenanthrenes; 5-methyl- and 5-phenyl-5,6-dihydrophenathridines;and 9H-dibenzopyran.The anions generated from 9-methyl-9-benzylfluorene, 9-benzyl-9-phenylfluorene, 5-methyl-5,6-dihydrophenanthridine, and 9H-dibenzopyran, as well as 9-methyl-9-(lithiomethyl)fluorene, did not undergo skeletal rearrangement when heated between 40 and 120 deg C for protracted periods.However, the anions derived from the 9-methyl-9-phenyl-, 9,9-diphenyl-, and 9,9-(2,2'-biphenylene)-9,10-dihydrophenanthrenes did undergo rearrangement with a shift of the 9-aryl group.With the anion of 5-phenyl-5,6-dihydrophenanthridine, some shift of the 5-phenyl was observed, but the principal rearrangement was ring contraction with the formation of N-phenyl-9-fluorenylamine.By noting which anions underwent skeletal rearrangement and which competing migrating groups in a given anion underwent a shift preferentially, we have formulated an appropriate geometrical view of the transition states involved.Furthermore, by generating the 2,2,2-triphenylethyl anion (as its lithium salt) from (a) 2-chloro-1,1,1-triphenylethane and Li, (b) 2-bromo-1,1,1-triphenylethane and n-BuLi, and (c) bis(2,2,2-triphenylethyl)mercury and n-BuLi, we attempted to learn whether such shifts were truly nucleophilic or whether SET processes were involved.Evidence for SET processes was obtained for the generation of (2,2,2-triphenylethyl)lithium by method a, but no ESR or CIDNP evidence for radical intermediates was observable when (2,2,2-triphenylethyl)lithium was produced by method c.
