Microwave‐Enhanced Rhodium‐Catalyzed [2+2+2] Cycloaddition Reactions To Afford Highly Functionalized Pyridines and Bipyridines

Abstract

Rhodium(I)-catalyzed [2+2+2] cycloaddition reactions of N-tosyl-, carbon-, and oxygen-tethered cyanodiynes in a completely intramolecular fashion have been optimized to afford highly functionalized pyridines by conventional and/or microwave heating. Microwaves have been shown to enhance the process by allowing the reaction to be conducted effectively in short reaction times. The methodology has been ex-

Recent Advances in Transition-Metal-Catalyzed [2+2+2]-Cyclo(co)trimerization Reactions

“…Another example of a fully intramolecular transitionmetal-catalyzed [2+2+2]-cyclocotrimerization reaction was recently reported by Parella and co-workers for the synthesis of fused tricyclic pyridines and bipyridines. 57 This study is an excellent example of the sensitivity of the reaction of focus and shows the importance of fine-tuning the reaction conditions. In particular, the solvent and method of heating were shown to have a dramatic effect on the reaction outcome.…”

Transition Metal-Mediated Synthesis of Monocyclic Aromatic Heterocycles

“…752 Thus, Tanaka developed the Rh(I)-catalyzed intermolecular [2+2+2] cycloaddition of electron-rich aryl ethynyl ethers with nitriles, providing single regioisomer of pyridine 6-179 under mild conditions. In addition, employment of isocyanates in this transformation furnishes pyridones 6-180 efficiently (Scheme 462).…”

Asymmetric Synthesis of Diastereo‐ and Enantiopure Bioxahelicene 2,2′‐Bipyridines

“…As our endeavor has resulted in the development a general methodology for the synthesis of (hetero)helicenes, we have decided to explore its potential also in the synthesis of bioxahelicene 2,2′‐bipyridines. Interestingly, the usefulness of the [2+2+2] cycloisomerization reaction in the racemic or asymmetric synthesis of axially chiral 2,2′‐bipyridines and their derivatives using various π‐electron systems (alkynes, nitriles, isocyanates) was elegantly demonstrated by Bönnemann et al, Saá et al, Itoh et al, Tanaka et al, Kotora et al and Pla‐Quintana, Roglans et al However, the [2+2+2] cycloisomerization strategy has never been used in the synthesis of bihelicene 2,2′‐bipyridines as, to the best of our knowledge, no C 2 symmetric racemic/enantiopure azahelicenes directly connected in the 2,2′ positions with respect to the nitrogen atom have been described in the literature as yet.…”