Sequential Metathesis in Oxa‐ and Azanorbornene Derivatives

Abstract

Ring‐opening metathesis (ROM), when applied to the synthesis of bicyclic alkenes, is the basis of ring‐opening‐metathesis polymerisation (ROMP). This polymerisation reaction can be suppressed in the presence of a second open‐chain olefin thus combining the ROM with an intermolecular cross metathesis (CM). In conveniently substituted bicyclic derivatives a third metathetical reaction — ring closing metathesis (RCM) — can be achieved, giving new substituted bicyclic systems. In this account the results of these tandem metathetical reactions performed on oxa‐ and azabicyclic norbornenic derivatives are highlighted. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

The domino way to heterocycles

“…Building on their earlier tandem ring-opening/cross-metathesis studies, 135 Arjona and Plumet have applied the ring-opening/ring-closing/cross-metathesis cascade 136 to the synthesis of various nitrogenous heterocycles. For example, bicyclic amides 470a,b reacted with ethene in the presence of Grubbs catalyst 428 to give 471a,b in 65 and 60% yields, respectively (Scheme 89).…”

Recent advances in the stereoselective synthesis of tetrahydrofurans

“…84 As shown below, treatment of 157a with a catalytic amount of Rh 2 (OAc) 4 affords tetrahydrofuran 160a in 92% yield and 3:1 dr (eq 47). 84b Taber suggests that the prominent reaction mechanistic pathway for these transformations involves insertion of the carbenoid into the C-H bond via a late, cyclic "chair-like" transition state (158) in which the substituents are placed in pseudoequatorial positions. In contrast, the minor diastereomers are believed to derive from a boat-like transition state that occurs earlier on the reaction coordinate (eq 48, 159).…”

Chemospecific Allylation and Domino Metathesis of 7‐Oxanorbornenes for Skeletal and Appendage Diversity

“…[3,4] In this regard, the norbornene skeleton is an interesting platform because it undergoes domino ROM/CM/RCM reactions to generate other complex skeletons. [5] Combinations of these domino metathesis reactions with other multicomponent coupling reactions (MCRs) are also being actively studied for the generation of artificial smallmolecule libraries with high degrees of molecular diversity. [6][7][8] In these researches, MCRs are generally used for generation of complex molecular architectures with appendage diversity, whereas metathesis is used for skeletal diversity.…”