Aspyrone (1) was elaborated in an optically pure form by a key reaction involving the highly diastereoselective addition of tetrahydropyranone enol ate to 2-tosyloxy-aldehyde and the subsequent in situ formation of an epoxide.
(R)-2-Tosyloxypropanal (4) was prepared from D-mannitol in a 7-step sequence (51% overall yield). Addition of dialkyl phosphonates to 4 in the presence of titanium isopropoxide and the subsequent treatment with DBU stereoselectively afforded, in one-pot, fosfomycin dimethyl (5a) and dibenzyl (5b) esters both in 58% isolated yield.
A convergent synthesis of optically active aspyrone.