Ring-Closing Metathesis Reactions on Azinium Salts: Straightforward Access to Quinolizinium Cations and Their Dihydro Derivatives

Abstract

The ring-closing metathesis reaction of 1-butenyl-2-vinylpyridinium salts and 2-butenyl-1-vinylpyridinium salts using Grubbs second generation and Hoveyda-Grubbs catalysts proved to be an efficient approach to 3,4-dihydro- and 1,2-dihydroquinolizinium salts and the corresponding quinolizinium derivatives by an improved thermal oxidation in the presence of Pd/C without solvent. A comparative study showed that the quinolizinium system was obtained in better yields through the 3,4-dihydroquinolizinium route, thus allowing the synthesis of quinolizinium derivatives or improvements in the yields of some examples reported previously.

Radical Hydroarylation of Functionalized Olefins and Mechanistic Investigation of Photocatalytic Pyridyl Radical Reactions

“…Exposure of the crude mixture to silica gel resulted in rapid quantitative conversion to the corresponding vinylpyridine, a product typically accessed through Stille cross-coupling with vinylstannane. 21 2-Chloropropene was similarly effective, providing secondary alkyl chloride 7 in 70% yield, again without undesired reduction of the resulting chloroalkane, and elimination during purification was not observed in this case. The reaction conditions were also tolerant of alkenyl fluorides, producing alkyl fluoride 8 in good yield.…”

“…Vinyl bromide was an effective coupling partner under the reaction conditions, affording alkyl bromide 6 in 78% yield with no further reduction to the corresponding ethylpyridine. Exposure of the crude mixture to silica gel resulted in rapid quantitative conversion to the corresponding vinylpyridine, a product typically accessed through Stille cross-coupling with vinylstannane . 2-Chloropropene was similarly effective, providing secondary alkyl chloride 7 in 70% yield, again without undesired reduction of the resulting chloroalkane, and elimination during purification was not observed in this case.…”

Beyond catalyst deactivation: cross-metathesis involving olefins containing N-heteroaromatics

“…The formation of seven- and eight-membered rings required high dilution. Few years later, the same authors showed that it was possible to oxidize 3,4-dihydroquinolizinium salts into their quinolizinium counterparts using Pd/C at high temperature ( Scheme 11 ) [ 48 ].…”

Intramolecular Direct C−H Arylation Approach to Fused Purines. Synthesis of Purino[8,9-f]phenanthridines and 5,6-Dihydropurino[8,9-a]isoquinolines§Dedicated to the memory of Keith Fagnou.

“…The higher yields of this intramolecular C−H arylation compared to the synthesis of purino[8,9- f ]phenanthridines are probably due to the flexible saturated linker in intermediates 10 that makes the C−H arylation more efficient even for ethylene-tethered chlorobenzene compared to o -phenylene-tethered bromobenzene. Attempts to oxidize 5,6-dihydropurino[8,9- a ]isoquinolines 11 to fully aromatic purino[8,9- a ]isoquinolines with use of diverse oxidants (MnO 2 , Pd/C, DDQ) failed. Crystal structures of both 5,6-dihydropurino[8,9- a ]isoquinolines 11a , b (Scheme and the SI) revealed a small distortion of the planarity caused by the saturated ethylene bridge (torsion angles of purine and benzene rings were ca.…”