SnCl 4 -mediated oxidative biaryl coupling reaction of 1-naphthol and subsequent ring closure of 2,2′-binaphthol to the dinaphthofuran framework

Reactions of 1-Naphthols with .PI.-Acceptor p-Benzoquinones: Oxidative Aryl Coupling vs. Non-Oxidative Electrophilic Arylation

“…Firstly, we investigated the oxidative biaryl coupling reaction of NPOHs 1a-f (including precursors for the synthesis of natural products) and the naphthol ether 1d 16) with Qs such as BQ, CA, and DDQ as p electron acceptors under various conditions. To determine the optimum conditions for the coupling reaction, detailed preliminary experiments on the oxidative dimerization were done with NPOH 1a as a substrate at room temperature (23°C), without light irradiation.…”

“…Similar reactions were explored using 1b or 1c, 16) which can be used as precursors for the synthesis of binaphthyl natural products (Table 1). 21) When using 1b as a substrate, a particular difference between the oxidations with BQ and CA was observed.…”

“…thols by means of chemical methods and electrolysis have been studied extensively, mixtures of dimeric, polymeric and quinoid compounds were usually generated. Next, we investigated the reactions of NPOHs 1e, f 16) using BQ or CA (Chart 1 and Table 1). When BQ was used as an acceptor, no reaction of 1e, f occurred at all in both cases (runs 14, 16), while in the case with CA, the non-oxidative electrophilic arylation of CA with 1e, f took place to give the corresponding napthol-quinone adducts (NPOH-Q; 7e, f) in poor yields (runs 15,17).…”

“…We have focused on the oxidative coupling (or dimerization) of 1-naphthols (NPOHs) in order to develop a method for constructing biaryl substructures, aiming at biomimetic synthesis of natural products such as 2,2Ј-binaphthols, 2,2Ј-binapthylquinones and their derivatives. 4) Oxidizing reagents used in the oxidative coupling reaction of hydroxyarenes include a variety of metal salts, 16) Lewis acids 17,18) and nitrosonium salts, 19) and hypervalent iodine-(III) reagents. 20) Recently, in particular, various oxidizing reagent systems for the coupling of 2-naphthols by using combinations of metal salts or metal complexes as a catalyst with aerial oxygen or dioxygen (O 2 ) have been developed: these catalysts include FeCl 3 -SiO 2 , CuSO 4 -Al 2 O 3 , CuSO 4 montmorillonite, CuCl-amine complexes, CuCl(OH)-TMEDA, and oxovanadium(IV) complexes.…”

“…We have reported an oxidative coupling reaction via electron donor-acceptor (EDA) complexes of 1-naphthols with a Lewis acid such as SnCl 4 or a semiconductor including ZrO 2 in the absence or presence of dioxygen (O 2 ). 16,22,24) This EDA chemistry could provide the basis for a simple method of constructing biaryl frameworks, leading to a biomimetic synthesis of natural products.…”