Total synthesis of hemibrevetoxin B and (7a.alpha.)-epi-hemibrevetoxin B

摘要: The total synthesis of hemibrevetoxin B (1) and (7aα)-epi-hemibrevetoxin (2) is described. the epimer was achieved through a convergent approach involving coupling carboxylic acid 17 carrying bicyclic pyran system with hydroxy compound 31 containing monocyclic system, thionation resulting diester 32 to dithionoester 33, photolytic closure oxepane enol ether 34, ketone cyclization dioxepane 40. Z-diene established using selenyl-Wittig reaction followed by syn elimination selenoxide diene. α-vinyl functionality installed Eschenmoser's salt methodology. linear sequential formation rings (65 → 67 73) method thionolactone nucleophilic addition regio/stereoselective hydroboration (67 68, 75 76). Elaboration side chains carried out in similar fashion as described for epimer. streochemistry ring junctures 1 2 intermediates leading them X-ray cristallographic analysis on compounds 45 54