Fig. 1

A Key synthetic strategies towards the target lactones. B Synthesis of key intermediate 7; a) 2,2-dimethoxypropane, DMF, MS 5 Å, 0 °C, 3 h, then rt overnight, 41%; b) Ph₃PCHCO₂Et, benzoic acid, toluene, reflux, 87%; c) H₂ (1 atm), Pd/C, EtOAc, rt, 93%; d) SO₃-Pyr, Et₃N/DMSO, DCM, rt, 87%. C Synthesis of key phosphonium salts 12 and 17; e) Heptanoyl chloride, AlCl₃, DCM, 0 °C, r.t, 30 min – 1 h, 73%; f) NBS, THF, H₂O, hv, r.t, 83%; g) PPh₃, acetone, reflux, 3 h, 82%. h) Heptyl bromide, K₂CO₃, CH₃CN, 24 h, reflux, 72%, or; KOH, EtOH, H₂O, 24 h, reflux, 76%; i) NBS, Bz₂O₂, DCM, reflux, 9 h, 48%. j) = g), 72%