Studies on Thermal Reactivity of β‐(1,2‐Allenyl)butenolides and 2‐Allyl‐3‐allenylcyclohex‐2‐enones

Abstract

A series of thermal pericyclic reactions of beta-allenylfuranones have been studied. It was observed that beta-allenylfuranones would undergo 1,5-hydrogen shift to afford a new type of trienes upon heating. Due to their high reactivity, these trienes would undergo subsequent pericyclic reactions based on the nature of the substituent group R: When R is an alkyl group, the intermediate 4a or 4b would undergo a further 1,7-hydrogen shift to afford a more stable conjugated triene 3; with R being phenyl or cyclopropyl group, the 1,7-hydrogen shift was inhibited and the 4-type conjugated triene would form a six-membered ring 5 via 6 pi-electrocyclization. Interestingly, introducing another C=C double bond into the triene intermediate (R = CH=CH2, the 18-type intermediate would undergo 8 pi-electrocyclization reaction to form an eight-membered ring. Such a transformation was also observed with 2-allyl-3-allenylcyclohex-2-enones. The deuterium-labeling mechanistic studies show that the alkyl groups at the allenyl moiety of 1 participated in the isomerization process via 1,7-hydrogen shifts between 18 A, 20 A, and 29 A.

Mn‐Catalyzed Dehydrocyanative Transannulation of Heteroarenes and Propargyl Carbonates through C−H Activation: Beyond the Permanent Directing Effects of Pyridines/Pyrimidines

“…Although only asingle example has been reported for using allenes as dienophiles in DA/retro-DAp rocesses, [8a] allenes are reactive unsaturated molecules and may well suffice. [9] Despite the possible duality of pyridines/pyimidines, these two areas evolved separately.W er easoned that such "permanent" DGs can be fully exploited by integration of C À Hactivation chemistry and DA/retro-DAreactions.T olower the energy barrier of the DA/retro-DAprocess,our strategy is to implement intramolecular reactions using electronically activated pyridines/pyrimidines.T ot his end, we designed heteroarenes bearing ad onating-group-activated pyridine/ pyrimidine ring as C À Hs ubstrates for coupling with allene precursors. [10,11] Although CÀHa ctivation with subsequent IMDAh as been reported in our previous work, [12] transformation of the DG was irrelevant.…”

Manganese(I)-Catalyzed Synthesis of Fused Eight- and Four-Membered Carbocycles via C–H Activation and Pericyclic Reactions

“…Consequently, different routes for efficient preparation of fused four- and eight-membered carbocycles have been developed in the past decades . For instance, Ma reported an efficient protocol for synthesis of eight-membered bicyclic compounds via [1,5]-hydrogen migration and 8π-electrocyclization . Meanwhile, metal-catalyzed ene–allene formal [2 + 2] cycloadditions have been reported for synthesis of [3,2,0]-fused cyclobutanes .…”

“…Moreover, 3bo was selectively reduced to 10 in 70% yield. Heating a mixture of 3bo and N -methylmaleimide afforded a bridged polycycle 9 (Scheme b), which may occur via 6π-electrocyclization followed by a Diels–Alder reaction . Rh­(III)-catalyzed coupling of 6ao with a diazo reagent afforded a C(7)-alkylation product 11 in excellent yield (Scheme c) …”

“…Subsequent regioselective migratory insertion of the Mn–C bond into the alkyne is followed by β-oxygen elimination of A and E to give the allenylation intermediate. For 3-alkenylindole, the allene B may undergo 1,7-H migration, furnishing a tetraene C , which undergoes 8π-electrocyclization to deliver product 3 . , Alternatively, the allene may follow an ene-reaction pathway to give a four-membered ring D . Subsequent Cope rearrangement furnishes the same product 3 .…”

Mn‐Catalyzed Dehydrocyanative Transannulation of Heteroarenes and Propargyl Carbonates through C−H Activation: Beyond the Permanent Directing Effects of Pyridines/Pyrimidines

“…[7,8] However,h arsh condi-tions are required, and the dienophiles have been limited to arynes or highly polarized alkynes (yanamines and ynamides). [9] Despite the possible duality of pyridines/pyimidines, these two areas evolved separately.W er easoned that such "permanent" DGs can be fully exploited by integration of C À Hactivation chemistry and DA/retro-DAreactions.T olower the energy barrier of the DA/retro-DAprocess,our strategy is to implement intramolecular reactions using electronically activated pyridines/pyrimidines.T ot his end, we designed heteroarenes bearing ad onating-group-activated pyridine/ pyrimidine ring as C À Hs ubstrates for coupling with allene precursors. [9] Despite the possible duality of pyridines/pyimidines, these two areas evolved separately.W er easoned that such "permanent" DGs can be fully exploited by integration of C À Hactivation chemistry and DA/retro-DAreactions.T olower the energy barrier of the DA/retro-DAprocess,our strategy is to implement intramolecular reactions using electronically activated pyridines/pyrimidines.T ot his end, we designed heteroarenes bearing ad onating-group-activated pyridine/ pyrimidine ring as C À Hs ubstrates for coupling with allene precursors.…”