Application of the diastereoselective photodeconjugation of α,β-unsaturated esters to the synthesis of gymnastatin H

The asymmetric synthesis of gymnastatin H has been achieved by using the photoisomerisation of a conjugated ester to its beta,gamma-unsaturated isomer through the protonation of a in situ generated dienol as key step. Thanks to diacetone D-glucose used as a chiral alkoxy group, the protonation occurred well onto one of the two diastereotopic faces with very high yields and selectivities. Moreover, by this way the configuration of the C-6 centre of the target molecule was controlled.