Total synthesis of (+)-milbemycin β3

(+)-Milbemycin β3(1) was prepared by total synthesis from (6S,8R,9S)-methyl 8,9-dimethyl-4-oxo-1,7-dioxaspiro[5.5]undeco-2-ene-2-carboxylate (2), (4R,6R)-4-methyl-6-phenylsulphonyl-(E)-hept-2-en-1-ol (3a), and 2-ethyl-4-methoxy-5-methylbenzoic acid (4) using Julia–Lythgoe and benzylic anion chemistry to establish the carbon framework and a Mitsunobu reaction to close the lactone ring.