Synthetic and Mechanistic Investigation of an Oxime Ether Electrocyclization Approach to Heteroaromatic Boronic Acid Derivatives

Abstract

A range of functionalized heteroaromatic boronic acid derivatives are readily accessed by a diboration/6π-electrocyclization sequence. This study revealed the surprising observation that there is a direct relationship between oxime ether stereochemistry and reactivity towards electrocyclization. Specifically, E-oxime ethers are found to be significantly more reactive than their Z-counterparts (stereochemistry relative to azatriene scaffold). In contrast, the configuration at the azatriene alkene terminus has little impact on reaction rates. Computational analysis offers a rationale for this observation; a N →C=C π* orbital interaction lowers the energy of the transition state in the electrocyclization of E-oxime ethers. Finally, unreactive Z-oxime ethers can be converted to the corresponding heterocyclic products by a photolytically promoted E→Z isomerization and electrocyclization sequence.

Design and Synthesis of Fused Pyridine Building Blocks for Automated Library Generation

“…General . Characterization and synthetic procedures for compounds 1 , 2 , 5 , 7 , 8 are reported elsewhere [10b,c] …”

DABCO‐Promoted Selective Photochemical C−N Coupling: Access to Unsymmetrical Azahelicenes

“…[13] Acyl oximes with fivemembered heterocyclic compounds as the spacers have been studied very little, although it is well known that the nature and size of the heterocycle can strongly affect both the photochemical process and the stability of the iminyl radical. [14] Therefore, studies on the photochemical cyclization of acyl oximes with heterocyclic spacers and the development of efficient methods for the synthesis of heteroannulated quinolines (heterophenanthridines) are urgent issues of modern organic chemistry and would provide access to these very valuable compounds for medicine and materials chemistry.…”

Facile synthesis of isoquinolines and isoquinolineN-oxidesviaa copper-catalyzed intramolecular cyclization in water

“…In 2009, Zhang and co-workers reported an interesting work involving the product selectivity control reactions to afford isoquinolines and isoquinolin-1(2 H )-ones by simple subtle structure modification of ortho -alkynylaryl aldehyde oxime derivatives. 14 Subsequently, Li, 15 Harrity, 16 Shi 17 and others 18 disclosed a rhodium( iii ), platinum(0), silver( i ) and gold( i )-catalyzed intramolecular cyclization reaction using the same or analogous starting materials for the synthesis of isoquinolines and their derivatives, respectively. However, despite these significant advances made in accessibility of isoquinolines and their derivatives, some challenging issues still remain in terms of the use of toxic organic solvents, precious metal catalysts, harsh reaction conditions, which lead to poor atom economy and are inconsistent with the principles of green chemistry.…”