Conformational bias in macrocyclic ethers and observation of high solvolytic reactivity at a masked furfuryl (=2-furylmethyl) C-atom

New polyhalogenated, twelve-membered. O-bridged cyclic C-15-ethers. having in common oxygenation at C(6) and a bromoallene side chain at C(4) (where C (1) is the bromoallene-chain terminus). were isolated from the red seaweed Laurencia obtusa from the Turkish Mediterranean Sea. i.e. the: 9.12-O-bridg ed obtusallene VII (5). the 6.9 :9.12-bis-O-bridged obtusallene V (3) and o btusallene VI (4), as well as the 6,9-O-bridged obtusallene VIII (8) and ob tusallene IX (9). The behaviour of portions of the macrocycle involved in f ast motion and their equilibrium position depend on the particular compound , revealing a sub;lc. conformational behavior of these macrocycles, while 8 and 9 show an unprecedented solvolytic reactivity at the masked furfuryl ( -2- furyimethyl) C-atom.