49623-71-4Relevant articles and documents
Visible-Light-Driven Carboxylation of Aryl Halides by the Combined Use of Palladium and Photoredox Catalysts
Shimomaki, Katsuya,Murata, Kei,Martin, Ruben,Iwasawa, Nobuharu
supporting information, p. 9467 - 9470 (2017/07/24)
A highly useful, visible-light-driven carboxylation of aryl bromides and chlorides with CO2 was realized using a combination of Pd(OAc)2 as a carboxylation catalyst and Ir(ppy)2(dtbpy)(PF6) as a photoredox catalyst. This carboxylation reaction proceeded in high yields under 1 atm of CO2 with a variety of functionalized aryl bromides and chlorides without the necessity of using stoichiometric metallic reductants.
Photocyclization of -(o-Tolyl)acetophenones: Triplet and 1,5-biradical reactivity
Wagner, Peter J.,Meador, Michael A.,Zhou, Boli,Park, Bong-Ser
, p. 9630 - 9639 (2007/10/02)
Several ring-substituted α-(o-tolyl)acetophenones undergo photocyclization to 2-indanol derivatives in high quantum efficiency in solution and in high chemical yield as solids. The mechanism for reaction involves triplet state δ-hydrogen atom abstraction that generates 1,5-biradicals. Quenching studies indicate that the n.π* excited triplets of these ketones react, with rate constants >108 s-1. Variations in triplet reactivity are ascribed to conformational equilibria that populate reactive and unreactive geometries to different extents. The α-aryl ring eclipses the carbonyl in the lowest energy geometry, from which the most favorable geometry for reaction can be reached by small bond rotations. α-(2,4,6-Triisopropylpheny)acetophenone forms the relatively long lived enol as well as indanol in solvent-dependent ratios; deuterium labeling indicates that the 1,5-biradical disproportionates to form enol. This does not happen with α-mesitylacetophenone, so its 54% cyclization quantum efficiency is ascribed to an internal triplet quenching that competes with hydrogen abstraction. This internal quenching is presumed to be of the charge-transfer type and does not appear to lead directly to 1,5-biradicals. 1-Methyl-2-phenyl-2-indanol is formed from α-(o-ethylpheny)acetophenone with a Z/E ratio of 20:1 in benzene and 2:1 in methanol. The 1,5-biradical intermediates were characterized by flash spectroscopy; they have lifetimes between 15 and 45 ns, with those derived from α-(o-isopropylphenyl) ketones being twice as long-lived as those derived from α-(o-methylphenyl) ketones, and show only a small solvent dependence. Biradical lifetimes and the diastereoselectivity of cyclization are interpreted in terms of biradical intersystem crossing occurring preferentially along the reaction coordinate for cyclization, such that the two processes effectively occur concurrently. The applicability of this concept to other biradicals is discussed.
Dipole-Stabilized Carbanions from Esters: α-Oxo Lithiations of 2,6-Substituted Benzoates of Primary Alcohols
Beak, Peter,Carter, Linda G.
, p. 2363 - 2373 (2007/10/02)
The synthetic utility of dipole-stabilized carbanions from esters is illustrated by the preparations, α-oxo lithiations, electrophilic substitutions, and cleavages of the 2,4,6-triisopropylbenzoates and the 2,6-bis(dimethylamino)-3,5-diisopropylbenzoates of primary alcohols, 2 and 3, respectively.Typical electrophiles used in this methodology include primary alkyl halides, aldehydes, ketones, trimethylsilyl chloride, and tri-n-butyltin chloride.Cleavages of the substituted esters of 2 are accomplished with lithium aluminum hydride while hydrolyses of derivatives of3 can be achieved under acidic conditions.The 2,6-substitutions of 2 and 3 are considered to enforce orthogonality of the carbonyl group and the phenyl ring and thereby to inhibit addition to the carbonyl by the organolithium base used for the metalation by placing the substituents in the trajectory for nucleophilic addition along the LUMO of the carbonyl.The acidic hydrolysis of 3 under conditions where 2 is stable is attributed to protonation of the dimethylamino group which provides subsequent assistance for nucleophilic addition.These metalations provide the key steps in the preparation of secondary α-lithio alcohol synthetic equivalents from primary alcohols.Lithiation of 1'-methylbenzyl 2,4,6-triisopropylbenzoate proceeds α to oxygen as expected, but attempts to prepare analogous unactivated tertiary α-lithio esters were unsuccessful.The lithiation of 2'-methoxyethyl 2,4,6-triisopropylbenzoate is followed by elimination of methoxide and α-oxo metalation of the resulting vinyl ester.Lithiation of allyl 2,4,6-triisopropylbenzoate provides 1-(2,4,6-triisopropylphenyl)-1,2-butanedione by rearrangement.
