Download full text in PDF Opens in a new window. Article suggestions will be shown in a dialog on return to ScienceDirect. ... Please enable JavaScript to use all the features on this page. ... The dihydro compound 14 related to the bicyclic core structure of dynemicin and calicheamicin/esperamicin was obtained by a [2,3] Wittig ring contraction of the cyclic ether 13. Similar attempts with 4 gave the 12-membered carbocycle 6 resulting from a [1,2] shift.