Intramolecular Diels-Alder cycloadditions of cis-cyclohexadienediols derived enzymatically from (2-azidoethyl)benzene. Construction of highly functionalized bridged isoquinoline synthons

(3aR,7aS)-4-(2-Azidoethyl)-2,2-dimethyl-3a,7a-dihydrobenzo[1,3]dioxole (22) was converted in two steps to trienes 23 and 24, which upon heating underw ent intramolecular Diels-Alder reactions to give mixtures of isomeric 11,11 -dimethyl-5-oxo-10,12-dioxa-4-azatetracyclo[6.5.2.0(1.6).0(9,13)]pentadec-1 4-ene-7-carboxylates 25, 26 and 27, 28, respectively. These products were s eparated and identified. For comparison, intermolecular Diels-Alder cycload dition of diene 22 with maleic anhydride was carried out. Products of this reaction, 1-(2-azidoethyl)-4,4-dimethyl-3,5,10-trioxatetracyclo[5.5.2.0(2,6 ).0(8,12)]tetradec-13-ene-9,11-diones (29 and 30) were converted to methyl ester analogues of 31 and 32 in a two-step sequence. The stereochemical out come of these cycloadditions is discussed as well as their possible utiliza tion in organic synthesis, especially in total synthesis of some alkaloids.