Synthesis and structure of novel dibenzo[b,i]-1-oxa-6-heteroecines containing group 15 heavier elements

A series of novel dibenzo[b, i]-1-oxa-6-heteroecines (4a-d) containing Grou p 15 heavier elements (P, As, Sb, and Bi) have been prepared via common 1,9 -dilithium intermediate (3). Single crystal X-Ray analysis of oxastibecine (4c) reveals that the two olefinic bonds in the ring system are both cis co nfiguration and the distance between the antimony and oxygen atoms is short er than the sum of the van der Waals radiis of each element, indicating the presence of a transannular interaction between the oxygen and hetero atoms .