Substituierte 9‐Oxabicyclo[4.2.1]‐ und 9‐Oxabicyclo[3.3.1]nonane III. neue ergiebige synthese von 2, 7‐dioxatwistan und endo ‐2‐hydroxy‐9‐oxabicyclo[3.3.1]nonen‐(6)

Iodine cleavage of the [3.3.1]‐iodomercuri compound 4 , easily prepared from cis , cis ‐cyclooctadiene‐(1,5) by oxymercuration of the monoepoxide 1 (→ 3 ) followed by treatment with potassium iodide, leads to three isomeric iodides 6, 7 , and 8 , the [3.3.1]‐ exo ‐iodo isomer 8 being the predominant product. Intramolecular substitution in 8 opens an attractive new route to unsubstituted 2,7‐dioxatwistane ( 19 ) [2], whereas dehydrohalogenation of 7 and 8 yields the unsaturated alcohol 17 [2], a suitable starting material for the preparation of substituted 2,7‐dioxatwistanes [2], 2,7‐dioxaisotwistanes ( e ) [2], and 2,8‐dioxa‐homotwistbrendanes ( f ).