[3 + 2] Coupling of Quinone Monoacetals by Combined Acid–Hydrogen Bond Donor

Abstract

The expeditious and efficient [3+2] coupling approach of quinone monoacetals 1 with alkene nucleophiles 2 by the action of an activated Brønsted acid in the presence of a hydrogen bond donor perfluorinated alcohol has been achieved. With the optimized combined acid, the reaction could proceed under mild conditions by only mixing the two reactants to afford the cycloadducts 3 in a short time (within 10 min) with good to quantitative yields.

Efficient Synthesis of Oxygenated Terphenyls and Other Oligomers: Sequential Arylation Reactions Through Phenol Oxidation–Rearomatization

“…A series of oxygenated terphenyls 3 aab – aad were obtained in good to excellent yields (Table 1, entries 1–3). In addition, when using an allyl‐protected oxygenated aryl nucleophile, the terphenyl 3 aae was formed in preference to a potential side reaction involving the alkene moiety of the allyl groups (Table 1, entry 4) 5c. The oxygenated phenol, anilide, and naphthalene were all found to be suitable coupling partners, giving terphenyls 3 aaf – aah (Table 1, entries 5–7).…”

Nucleophilic Arylation of Halopurines Facilitated by Brønsted Acid in Fluoroalcohol

“…The success of the metal-free coupling reaction relies on the use of HFIP as the solvent. Although the precise role of HFIP [44,45,46] remains unclear, we presume that HFIP can increase the acidity of TfOH (Brønsted acid activation by H-bond donor) to enhance the reactivity of halopurine electrophiles through the purine nitrogen atoms [47,48,49,50]. Importantly, HFIP offers a means of improving the leaving group ability of the chloride atom in the purine substrates through hydrogen bonding as well as solvation [51].…”

Tin Tetrachloride‐Catalyzed Regiospecific Allylic Substitution of Quinone Monoketals: An Easy Entry to Benzofurans and Coumestans

“…Sartori realized an S N 2′ reaction of quinone monoacetals and phenols in the presence of a stoichiometric amount of EtAlCl 2 leading to the coupling products only in 25–60% yields 6. Significantly, an attractive strategy has been established recently for controlling the regioselectivity of the S N 2′ reactions of quinone monoketals with electron‐rich arenes7a,c or alkenes7b (Scheme , A ). In these reactions, the ketal moiety was required to be activated, depending on the nature of nucleophiles, by an unusaul sandwiched solid acid,7a a Brønsted acid activated by a hydrogen bond donor (perfluorinated alcohol)7b or by a Pt(IV)‐aqua complex 7c.…”

“…Significantly, an attractive strategy has been established recently for controlling the regioselectivity of the S N 2′ reactions of quinone monoketals with electron‐rich arenes7a,c or alkenes7b (Scheme , A ). In these reactions, the ketal moiety was required to be activated, depending on the nature of nucleophiles, by an unusaul sandwiched solid acid,7a a Brønsted acid activated by a hydrogen bond donor (perfluorinated alcohol)7b or by a Pt(IV)‐aqua complex 7c. The high selectivity of these reactions is believed to lie in the steric block of the β‐position arising from the activation, which leads to an attack of nucleophiles at the less hindered α‐carbon of quinone monoketals 7.…”