Palladium‐Catalyzed Intermolecular [4+1] Spiroannulation by C(sp³)−H Activation and Naphthol Dearomatization

Abstract

A novel palladium‐catalyzed [4+1] spiroannulation was developed by using a C(sp3)−H activation/naphthol dearomatization approach. This bimolecular domino reaction of two aryl halides was realized through a sequence of cyclometallation‐facilitated C(sp3)−H activation, biaryl cross‐coupling, and naphthol dearomatization, thus rendering the rapid assembly of a new class of spirocyclic molecules in good yields with broad functional‐group tolerance. Preliminary mechanistic studies indicate that C−H cleavage is likely involved in the rate‐determining step, and a five‐membered palladacycle was identified as the key intermediate for the intermolecular coupling.

Photoredox‐Catalyzed Thiocyanative Cyclization of Biaryl Ynones to Thiocyanated Spiro[5.5]trienones: An External‐Oxidant‐ and Transition‐Metal‐Free Approach

“…However, when the reaction was carried out by taking H 2 O as only solvent, trace amount of 2 a was formed, which might be attributed to the lower solubility of organic compounds in aqueous solvent (entry 8). Further, we checked this transformation with bi-phasic solvent in a different ratio (entries [9][10][11]. Gratifyingly, the use of MeCN : H 2 O (25 : 1) delivered the expected dearomatized product 2 a in 92 % yield (entry 8).…”

“…[10] In light of this, numerous effective protocols have been devised for the synthesis of spirocycles. [11] Spirocyclic synthesis often largely relies on dearomatization, including electrophilic/nucleophilic, oxidative, and a variety of transition metal-mediated dearomatization. [12] In addition to the above-mentioned approaches, nowadays, cascade ipso cyclization reactions of alkyne through a radical process have emerged as one of the most effective synthetic ways for the formation of various spirocyclics (Scheme 1b).…”