We report our synthetic studies towards the synthesis of the C3–C14 fragment of alchivemycin A. The synthesis featured an asymmetric alkylation with excellent diastereoselectivity and a one-pot Julia–Kocienski olefination with excellent E-selectivity. An intramolecular Diels–Alder reaction was employed to construct the highly functionalized cis-decalin framework. Interestingly, the stereochemical outcome was not expected to generate the two stereoisomers 20 and 21 instead of the desired cis-decalin 5. The detailed mechanism of this transformation was discussed. These synthetic endeavors have offered us a number of crucial insights for the synthesis of the complex natural product alchivemycin A.