A highly convergent synthesis of the proposed mandelalide A aglycone is reported. The cornerstones of the synthetic strategy include the following: E-selective intramolecular Heck cyclization, Masamune-Roush olefination, Stork-Zhao-Wittig olefination, modified Prins cyclization; Sharpless asymmetric dihydroxylation followed by Williamson-type etherification, Julia-Kocienski olefination, Brown crotylation, and Brown allylation reactions.
In this article the formal total synthesis of mandelalide A has been described in details. The highly convergent and flexible strategy developed for mandelalide A involved the construction of key building blocks ent-9 and 7, and their assembly to the target compound. For the synthesis and coupling of these building blocks, the Brown's crotylation, Sharpless asymmetric dihydroxylation followed by in situ Williamson type etherification, modified Prins cyclization, Masamune-Roush olefination and Heck cyclization were employed, the latter being crucial for the highly stereoselective formation of the macrocycle of mandelalide A. Initially, Julia Kocienski olefination, ring-closing metathesis reaction were investigated for the synthesis of the aglycone of the proposed structure of the mandelalide A, and found to be unsuccessful.
A highly convergent synthetic approach towards the macrolactone polyketide tianchimycin A is described. Notable features of our synthetic approach include highly stereoselective Myers alkylation, substrate controlled anti aldol reaction, and Masamune-Roush olefination.
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