16308-92-2Relevant articles and documents
An Enzymatic Route to α-Tocopherol Synthons: Aromatic Hydroxylation of Pseudocumene and Mesitylene with P450 BM3
Dennig, Alexander,Weingartner, Alexandra Maria,Kardashliev, Tsvetan,Müller, Christina Andrea,Tassano, Erika,Schürmann, Martin,Ruff, Anna Jo?lle,Schwaneberg, Ulrich
, p. 17981 - 17991 (2017)
Aromatic hydroxylation of pseudocumene (1 a) and mesitylene (1 b) with P450 BM3 yields key phenolic building blocks for α-tocopherol synthesis. The P450 BM3 wild-type (WT) catalyzed selective aromatic hydroxylation of 1 b (94 %), whereas 1 a was hydroxylated to a large extent on benzylic positions (46–64 %). Site-saturation mutagenesis generated a new P450 BM3 mutant, herein named “variant M3” (R47S, Y51W, A330F, I401M), with significantly increased coupling efficiency (3- to 8-fold) and activity (75- to 230-fold) for the conversion of 1 a and 1 b. Additional π–π interactions introduced by mutation A330F improved not only productivity and coupling efficiency, but also selectivity toward aromatic hydroxylation of 1 a (61 to 75 %). Under continuous nicotinamide adenine dinucleotide phosphate recycling, the novel P450 BM3 variant M3 was able to produce the key tocopherol precursor trimethylhydroquinone (3 a; 35 % selectivity; 0.18 mg mL?1) directly from 1 a. In the case of 1 b, overoxidation leads to dearomatization and the formation of a valuable p-quinol synthon that can directly serve as an educt for the synthesis of 3 a. Detailed product pattern analysis, substrate docking, and mechanistic considerations support the hypothesis that 1 a binds in an inverted orientation in the active site of P450 BM3 WT, relative to P450 BM3 variant M3, to allow this change in chemoselectivity. This study provides an enzymatic route to key phenolic synthons for α-tocopherols and the first catalytic and mechanistic insights into direct aromatic hydroxylation and dearomatization of trimethylbenzenes with O2.
Visible Light Induced Reduction and Pinacol Coupling of Aldehydes and Ketones Catalyzed by Core/Shell Quantum Dots
Xi, Zi-Wei,Yang, Lei,Wang, Dan-Yan,Feng, Chuan-Wei,Qin, Yufeng,Shen, Yong-Miao,Pu, Chaodan,Peng, Xiaogang
, p. 2474 - 2488 (2021/02/05)
We present an efficient and versatile visible light-driven methodology to transform aryl aldehydes and ketones chemoselectively either to alcohols or to pinacol products with CdSe/CdS core/shell quantum dots as photocatalysts. Thiophenols were used as proton and hydrogen atom donors and as hole traps for the excited quantum dots (QDs) in these reactions. The two products can be switched from one to the other simply by changing the amount of thiophenol in the reaction system. The core/shell QD catalysts are highly efficient with a turn over number (TON) larger than 4 × 104 and 4 × 105 for the reduction to alcohol and pinacol formation, respectively, and are very stable so that they can be recycled for at least 10 times in the reactions without significant loss of catalytic activity. The additional advantages of this method include good functional group tolerance, mild reaction conditions, the allowance of selectively reducing aldehydes in the presence of ketones, and easiness for large scale reactions. Reaction mechanisms were studied by quenching experiments and a radical capture experiment, and the reasons for the switchover of the reaction pathways upon the change of reaction conditions are provided.
Selective lithiation of 4- and 5-halophthalans
Garcia, Daniel,Foubelo, Francisco,Yus, Miguel
experimental part, p. 991 - 1005 (2010/10/03)
The reaction of 4- and 5-halophthalans 5 with lithium and a catalytic amount of DTBB at -78 °C leads to the formation of the corresponding functionalized organolithium intermediates 6 and 11, which by reaction with carbonyl compounds give, after hydrolysis, the expected substituted phthalans 8 and 13, respectively. When after reaction with the carbonyl compound the system is allowed to react at 0 °C, a second lithiation occur: A reductive opening of the heterocycle takes place with some regioselectivity leading to new organolithium intermediates 9 and 14/15 that by reaction with electrophiles lead, after hydrolysis, to polyfunctionalized molecules 10 and 16/17, respectively.
