Strong Conformational Preferences of Heteroaromatic Ethers and Electron Pair Repulsion

Abstract

Electron-pair repulsion in 2-methoxyheteroarenes is important for N, but not for O or S heteroatoms.

A General Approach to (Trifluoromethoxy)pyridines: First X‐ray Structure Determinations and Quantum Chemistry Studies

“…By DFT calculations, barriers of rotation of about 8 kcal mol -1 for 2-methoxypyridine and of about 3 kcal mol -1 for 3-methoxypyridine were calculated, which are in excellent agreement with our MP2 calculations. [28] After protonation of the ring nitrogen atom, the syn conformer becomes more stable.…”

Synthetic Studies on Pseudo‐Dimeric Lycopodium Alkaloids: Total Synthesis of Complanadine B

“…xv As an alternative to the carbamate and sulfamate derivatives, we turned to a methoxy derivative ( 19c ). Methoxy substitution on pyridines, as has been previously proposed by us xvi and by Corey and Chein, xvii is also inductively electron-withdrawing and, additionally, accomplishes steric shielding of the pyridine nitrogen (as a result of minimized dipoles of the lones pair on the pyridine nitrogen and oxygen substituent). We were also hopeful that we could directly remove the methoxy group utilizing the Ni-catalyzed strong bond activation methods introduced by Martin, xviii Garg, xix Hartwig xx and Agapie.…”

Synthetic Studies on Pseudo‐Dimeric Lycopodium Alkaloids: Total Synthesis of Complanadine B

“…However, the requisite substrates (i.e., 19 a and 19 b) failed to undergo Ir I -catalyzed borylation when the conditions of Hartwig, Miyaura, and coworkers were used, most likely because of the reduced capability of these substrates to bind in an h 2 fashion to the metal center before the C À H activation step. A methoxy substituent on pyridines, as has been previously proposed by us [16] and by Corey and Chein, [17] is inductively electron-withdrawing and, additionally, sterically shields the pyridine nitrogen atom (as a result of minimized dipoles of the lone pairs on the pyridine nitrogen and oxygen substituent). A methoxy substituent on pyridines, as has been previously proposed by us [16] and by Corey and Chein, [17] is inductively electron-withdrawing and, additionally, sterically shields the pyridine nitrogen atom (as a result of minimized dipoles of the lone pairs on the pyridine nitrogen and oxygen substituent).…”