Selective synthesis of unsymmetrical 2,2′-dihydroxylated biaryls via electrophilic arylation of metal phenolates with p-benzoquinone monoketals

Polycyclic xanthone natural products: structure, biological activity and chemical synthesis

“…The Kelly synthesis was the first hexacyclic xanthone synthesis and utilized an efficient strategy for xanthone formation previously reported by Brassard and coworkers (Scheme 4). 25 …”

“…This was the first example of such a biaryl bond formation using sub-stoichiometric amounts of a metal. 14b, 25 The C ring was then assembled using 6π-photochemical electrocyclization to yield 57 after cleavage of the silyl protecting group. The group then envisioned the use of an oxa -Michael/retro-Michael Friedel-Crafts annulation sequence to merge the ABCD ( 57 ) and F ( 58 ) rings into the desired hexacyclic ring-system.…”

Synthesis and Biological Evaluation of ABCD Ring Fragments of the Kibdelones

“…A report by Sartori and co-workers described the use of stoichiometric amounts of Et 2 AlCl to afford biaryls from quinone monoketals and phenols. [13] Unfortunately, latter conditions did not effect conversion of 9 and 16 to biaryl product 17. Since the desired B-D ring connection was established through this unexpected coupling, we conducted an extensive screen of both Brønsted and Lewis acids to improve the yield of the transformation.…”

Coupling of Quinone Monoacetals Promoted by Sandwiched Brønsted Acids: Synthesis of Oxygenated Biaryls

“…In contrast to the established addition chemistry of quinone monoacetals regarding the reactivity of the a,b-unsaturated carbonyl group, methods for utilizing the allyl acetal functionality are quite limited for the reactions with nucleophiles. In fact, reactions regarding the introduction of nucleophiles to the allylic position of the acetal units (which also corresponds to the a position of the a,b-unsaturated carbonyl) have rarely been reported, [4,5] thus significant advances in substitution chemistry are possible. Herein, we describe a general protocol for the introduction of nucleophiles to quinone monoacetals by substitution utilizing the unusual protons in polyanions, namely, sandwiched Brønsted acids, as activators.…”

“…The latter case mainly gave some chlorinated products derived from 1 a. Also, classical Lewis acids (Ti(OiPr) 4 and SnCl 4 ) as well as Brønsted acids (AcOH, CF 3 CO 2 H, HCl, triflic acid, and ptoluenesulfonic acid at various pH values) were screened in solvents such as dichloromethane, acetonitrile, and hexafluoroisopropanol (HFIP), and in all cases the substituted product 3 aa was not produced in good yield. [7] Thus, the role of the activator required for the substitution of quinone monoacetals was reconsidered at this stage.…”