An approach to the total synthesis of lankacidins: synthesis of the requisite building blocks

A strategy for a total synthesis of lankacidin C 1 is outlined and the requisite building blocks synthesised. The azetidinone 4 was prepared from methyl but-2-ynoate 6 via a route which features the stereoselective addition of a tributyltin cuprate to the alkyne, an asymmetric aldol condensation and formation of the azetidinone by an intramolecular Mitsunobu reaction. The aldehyde 3 was prepared from dimethyl malate 18 and the sulfone 3 from prop-2-ynol 27 again using asymmetric aldol reactions as key steps.