Oxidative C–H functionalization: a novel strategy for the acetoxylation/alkoxylation of arenes tethered to 3,4-dihydroisoquinolines

Dehydrogenative (Hetero)arene Alkoxylations Triggered by PdII‐Catalyzed C(sp2)–H Activation and Coordinating Substituent: PdII,III or PdIV Complex as Key Intermediate?

“…In 2010, Wang and Yuan noted, however, that the alkoxylation of N ‐methoxybenzamides (Entry 10) through Pd II /Pd 0 and Pd II /Pd III pathways cannot be completely excluded, whereas in 2015 Cui, Wu, and co‐workers suspected the possibility of a Pd III intermediate in the alkoxylation of 1,2‐diaryldiazene oxides (Entry 24) . In 2011/2012, Reddy's team proposed a Pd II /Pd 0 catalytic cycle from N ‐(2‐benzoylphenyl)benzamides (Entry 11) and 2‐arylquinazolin‐4(3 H )‐ones (Entry 21), but – nevertheless – a Pd IV intermediate for the DAA of 1‐aryl‐3,4‐dihydroisoquinolines (Entry 20) . According to Table , coordination of nitrogen to palladium occurs through a dative or a covalent bond, depending on its substitution.…”

Transition‐Metal‐Catalyzed Acyloxylation: Activation of C(sp2)–H and C(sp3)–H Bonds

“…After screening of different oxidants, PhI(OAc) 2 was identified as the most effective, at 80 °C in a 1,2‐dichloroethane/Ac 2 O mixture, in terms of the highest levels of conversion (Scheme ). For alkoxylation, heating at reflux in ethanol or methanol rather than acetic anhydride resulted in products in good yields . Pd 0 /Pd II or Pd II /Pd IV redox cycles are assumed in palladium‐catalyzed C–H functionalization reactions.…”

“…For alkoxylation, heating at reflux in ethanol or methanol rather than acetic anhydride resulted in products in good yields. [24] Pd 0 /Pd II or Pd II /Pd IV redox cycles [25] are assumed in palladiumcatalyzed C-H functionalization reactions. The presence of Pd IV complexes in C-H oxidation reactions was first suggested in 1971 [26] and was later confirmed by X-ray diffraction.…”

Pd(OAc)2-catalysed regioselective alkoxylation of aryl (β-carbolin-1-yl)methanones via β-carboline directed ortho-C(sp2)–H activation of an aryl ring

“…Essentially to improve the yield of 4aa, an optimization study involving the use of Pd(OAc) 2 as the catalyst in the presence of different oxidants and additives was carried out and the results are summarized in Table 1. Enhancing the amount of K 2 S 2 O 8 from 1 to 3 equiv improve the yield from 20% to 30% but further increase in amount of oxidant had no significant effect (compare entries [10][11][12]. Enhancing the amount of K 2 S 2 O 8 from 1 to 3 equiv improve the yield from 20% to 30% but further increase in amount of oxidant had no significant effect (compare entries [10][11][12].…”

“…In this context, the transition-metal catalyzed functionalization of ubiquitous but inert C-H bonds into C-C or C-X (X = halogen, O, N, S) bonds are of significant importance. 3 18 Ka mal (2014 ) 17 Kuang (201 4) 16 Wang (2010) 8 S ong ( 2014) 15 S un (2 014) 13 Urr iolabeitia (2015) 19 S un (2 013) 12 Wan g (2012) 9 S un (2012 ) seminal contributions of Sanford,[6][7] who demonstrated that the dehydrogenative coupling of aryl ring with alcohol under oxidative conditions, promoted by palladium in high oxidation states, affords alkoxylated aryl derivatives, there has been notable progress in the area [8][9][10][11][12][13][14][15][16][17][18][19][20] which is summarized in Fig. Among them, the directing group C-H activation is considered to be one of the most versatile strategies to achieve C-C and C-X couplings with good yields and selectivity, especially for C(sp2)-H bonds.…”