The efficient and concise synthesis of cytotoxic 5, 6-dihydro-α-pyrone (+)-brevipolide H has been accomplished in 12 long linear steps with 8.65% overall yield from readily available chiral synthons, D-galactal and L-ethyl lactate. The features of this synthesis are highly diastereoselective Simmons-Smith cyclopropanation and carbohydrate-based chiron approach to rapid access to key 5, 6-dihydro-α-pyrone skeleton.