2,3,4,5-Tetrahydrobenzo[b]oxepins are present in a number of natural products (eg, heliannuols C and D 1 or plumbagic acid lactone). 2 3,4,5,6-Tetrahydro-2H-benzo[b]oxocines occur in heliannuols A and K, 1, 3, 3a, 3b and 3c helianane 4 and protosappanine B. 5, 5a and 5b 2,5-Dihydrobenzo[b]oxepins occur in heliannuol B 1 and in radulanins A, H and L. 6, 6a, 6b, 6c, 6d, 6e and 6f 5,6-Dihydro-2H-benzo[b]oxocines are present in heliannuols G and H, 4 ...