Nonaflates from 8-oxabicyclo[3.2.1]oct-6-en-3-ones as building blocks for diversity-orientated synthesis:: Preparation, Heck-couplings and subsequent Diels-Alder reactions

A series of bicyclic alkenyl nonaflates was prepared in good yields by deprotonation of the corresponding 8-oxabicyclo[3.2.1]oct-6-en-3-ones and a sulfur relative with LDA followed by trapping with nonafluorobutanesulfonyl fluoride (NfF). The resulting compounds undergo Heck couplings to methyl acrylate under standard conditions, generally providing bicyclic dienes in satisfactory yields. For nonaflates 2 and 12 a novel base-promoted fragmentation reaction to substituted furan derivatives was observed. Several Diels-Alder reactions of the bicyclic dienes were conducted leading to polycyclic compounds. Whereas the diastereofacial selectivity with respect to the oxygen or sulfur bridge of the dienes is excellent, the exo/endo selectivity strongly depends on the substitution patterns of the bicyclic diene and the dienophile. The results presented demonstrate the potential of bicyclic nonaflates to serve as versatile building blocks in diversity-orientated synthesis.