SYNTHESIS OF SALINOMYCIN

Salinomycin, a commercially significant coccidiostat isolated from Str eptomyces albus, has been synthesised from three principal fragments. Key steps include (a) the use of eta(3)-allylmolybdenum cationic compl exes 21a,b for the stereoselective construction of two contiguous ster eogenic centres in fragment 5a; (b) the electrophilic cyclisation of 2 -(prop-2-ynyl)-2-hydroxyoxanes to give molybdenum and chromium carbene complexes which are precursors to the furan fragment 7; (c) the diast ereoselective oxidation of a 1,5-diene with potassium permanganate to generate four stereogenic centres in a single step leading to fragment 8; (d) the oxidative rearrangement of acylfuran 89 en route to the 1, 6,8-trioxadispiro[4.1.5.3]pentadec-13-ene dispiroacetal core; and fina lly (e) the use of an allenol ether as an acyl anion equivalent togeth er with the stereoselective hydrolysis of allenol ether intermediate 1 12 in an alternative synthesis of the dispiroacetal core.