Cu(0)/Selectfluor system-catalyzed intramolecular Csp2-H/Csp2-H cross-dehydrogenative coupling (CDC)

Copper‐Catalyzed Cross‐Dehydrogenative Coupling Reactions

“…An intramolecular catalytic C(sp 2 )À H/C(sp 2 )À H dehydrogenative cross-coupling of 2-arylbenzaldehyde (77) using Cu(0)/Selectfluor was developed by Bao et al [39] The strategy could synthesize xanthone derivatives (78) using mol% Cu(0), equiv. Selectfluor as oxidant, MeCN as solvent at 100°C for 24 h (Scheme 24).…”

Recent advances in the synthesis of xanthones and azaxanthones

“…158 4.1.2.1 Cyclization of diaryl ethers to xanthones by a crossdehydrogenative coupling. After the pioneering work of Wang et al 159 in 2012 on the synthesis of xanthones via a rhodiumcatalysed cross-dehydrogenative coupling (CDC) starting from 2-aryloxybenzaldehydes, alternative transition-metal catalysed strategies to construct the xanthone scaffold have been developed (Scheme 11) [160][161][162][163] For example, Wertz et al 160 reported an elegant and straightforward procedure for the synthesis of the xanthone core through a FeCp 2 -catalysed CDC reaction via a base-promoted homolytic aromatic substitution. Under the optimized conditions, several 2-aryloxybenzaldehydes bearing both electron-donating and electron-withdrawing substituents were coupled efficiently to give the corresponding xanthones with yields ranging from 30 to 78% (Scheme 11).…”

“…The authors extended the scope of this reaction not only to xanthones, but also to thioxanthones and fluorenones in moderate to good yields. 161 Recently, Bao et al 162 described a Cu(0)/Selectfluor system-catalysed intramolecular Csp 2 -H/Csp 2 -H bond CDC of 2-aryloxybenzaldehydes (Scheme 11). Interestingly, when in the presence of a substituent in the ortho position to the formyl group on the 2-aryloxybenzaldehyde, regioisomers were obtained.…”

“…Besides the clear advantages related to the use of an inexpensive and low-toxic copper catalyst and relatively mild reaction conditions, this procedure also accepts a wide variety of substituent groups such as F, Cl, Br, OCF 3 , CF 3 , Ph, OPh, iPr, and iBu, which provides opportunities for further molecular modifications. The authors were able to expand the use of this methodology for the synthesis of 9H-thioxanthen-9-one and 10,10-dioxide and phenanthridin-6 (5H)-one derivatives 162 and, interestingly, this process could be conducted successfully on a gram scale for a simple oxygenated xanthone (80% yield). A plausible mechanism for the [RuCl 2 ( p-cymene) 2 ] 2 -catalysed cyclization reaction was proposed and involves the formation of a cyclic seven membered transition state by addition of TBHP followed by reductive elimination to afford the desired compounds 61.…”

Selectfluor as “Fluorine-Free” Functional Reagent Applied to Organic Synthesis under Transition Metal-Free Conditions

“…这些方法相较于 Selectfluor 与过渡金属协同催化的 反应而言 [102][103] , 避免了使用昂贵的过渡金属, 反应体 系简单, 且反应条件更加温和, 表现广泛的底物适用性 及高效的区域选择性, 尤其是在复杂的环化反应中, 体 现出优异的官能团耐受性. 相对可见光诱导的有机反应 而言 [104][105] , Selectfluor 作为自由基引发剂, 替代了催化 效果不佳的光敏剂及传统的过渡金属光催化剂, 具有绿 色环保、经济高效等优点.…”