Assembly of a Benzo‐Fused Bridged Ketone Scaffold from 1,5,10‐Enediynes through One‐Pot Ruthenium‐Catalyzed Cyclization/Iodine‐Mediated Oxidative Ring Expansion

Abstract

In the presence of a cationic Ru catalyst, 1,6-diynes bearing a terminal styryl moiety underwent [2+2+2] cyclization to produce dehydrobiphenylenes fused with a five-membered ring. Although the cycloadducts were unstable toward purification, their one-pot iodine-mediated ring expansion successfully afforded unprecedented bridged ketone products containing a benzo-fused bicyclo[3.2.1] framework.

Small rings in the bigger picture: ring expansion of three- and four-membered rings to access larger all-carbon cyclic systems

“…A similar electrocyclic ring opening leading to benzocyclooctatrienones has also been reported by Yamamoto, and featured a one-pot ruthenium-catalysed cyclisation-iodine-mediated oxidative ring expansion. 117 4.1.2. Other sigmatropic rearrangements.…”

Nonplanar Tub-Shaped Benzocyclooctatetraenes via Halogen-Radical Ring Opening of Dihydrobiphenylenes

“… 15 Moreover, a tandem Ru-catalyzed [2+2+2] cyclization/iodine-mediated ring expansion of enediynes led to a straightforward assembly of benzo-fused bridged ketones. 16 However, to the best our knowledge, the radical opening of benzo-fused cyclohexadienes has not been investigated even though such combined processes have synthetic potential for accessing interesting functionalized scaffolds. Herein, we report an efficient tandem process based on a Ru-catalyzed [2+2+2] cycloaddition of arylenynes 1 with alkynes 2 to 1,8b-dihydrobiphenylenes 3 ( 14 ) followed by halogen-radical ring opening to benzocyclooctatetraenes 4 ( Scheme 1 ).…”

“…Interestingly, the heteroannulated benzocyclooctatetraenes 6a and 6b could be assembled in moderate yields via a one-pot, two-step process from arylenynes 5a and 5b bearing an O and a NTs group as linkers ( Scheme 3 , eq 1). 16 Double tandem processes were also accessible. Thus, a simple and straightforward entry to the linear benzodiCOT 9 (benzo[1,2:4,5]di[8]annulene), 22 an appealing nonbenzenoid PAH structure with intriguing electronic and aromatic properties, 23 was achieved from 1,4-diethynyl-2,5-divinylbenzene 7 .…”

“…This type of cyclohexadiene has been utilized in efficient synthetic manipulations such as oxidations and Diels–Alder reactions . Moreover, a tandem Ru-catalyzed [2+2+2] cyclization/iodine-mediated ring expansion of enediynes led to a straightforward assembly of benzo-fused bridged ketones . However, to the best our knowledge, the radical opening of benzo-fused cyclohexadienes has not been investigated even though such combined processes have synthetic potential for accessing interesting functionalized scaffolds.…”

“…Interestingly, the heteroannulated benzocyclooctatetraenes 6a and 6b could be assembled in moderate yields via a one-pot, two-step process from arylenynes 5a and 5b bearing an O and a NTs group as linkers (Scheme , eq 1) . Double tandem processes were also accessible.…”