Synthesis of 3‐Spiro Cycloalkenes Fused 7‐Aza‐2‐indalones from 3,3′‐di‐ or N,3,3′‐tri‐ allyl/homoallyl/pentenyl 7‐Aza‐2‐indalones via Ring Closing Metathesis using Grubbs‐II Catalyst

A facile and efficient synthesis of 3‐spiro cycloalkene fused 7‐aza‐2‐indalones from 3,3′‐di‐ or N,3,3′‐tri‐ allyl/homoallyl/pentenyl 7‐aza‐2‐indalones via ring‐closing metathesis (RCM) using Grubbs‐II catalyst has been achieved. The scope of the reaction has been demonstrated by synthesizing spiro products of various ring sizes (n=5, 7, and 18), utilizing 2‐indalone/7‐azaindalone and various alkenylation agents such as allyl/homoallyl/pentenyl bromides as substrates. In addition to usual RCM products, a cross metathesis (CM) product was observed when the substrate was N,3,3′‐triallylated derivative from 2‐indalone. Notably, a macrocyclic, 18‐membered bis‐spirodiene of N‐methyl‐7‐azaindalone was observed by means of intermolecular ring‐closing metathesis (RCM‐RCM). Also, Structures of a few representative spiro‐annulated products were evidenced with single crystal XRD analysis. Furthermore, a plausible mechanism for the products is discussed. [ABSTRACT FROM AUTHOR]