Allylation-Isomerization-RCM Strategy for Benzo-Fused 1,4-Heteroatom Heterocycles

Significance

A new approach for the synthesis of 1,4-benzodioxins, -benzoxazines, -benzodi­thiin, and 1,4-benzoxathiin utilizing a Grubbs ring-closing metathesis (RCM) reaction as the key step is reported. Initially, bis(vinyloxy)benzenes as RCM precursors were successfully tested, but this route was plagued by irreproducible and low yields, not to mention the use of stannanes. Thus, the synthetic sequence of choice became allylation-isomerization-RCM which proceeded in modest to good yields over these three steps. An attempt to prepare1,4-benzothiazine failed at the isomerization step due to loss of allyl or protecting groups.