Study for diastereoselective aldol reaction in flow: synthesis of (E)-(S)-3-hydroxy-7-tritylthio-4-heptenoic acid, a key component of cyclodepsipeptide HDAC inhibitors

Abstract Flow synthesis of (E)-(S)-3-hydroxy-7-tritylthio-4-heptenoic acid (5), a key component of cyclodepsipeptide histone deacetylase inhibitors was achieved. An efficient flow system for the synthesis of α, β-unsaturated ester 8 was established using a flow reactor column packed with polymer-supported 1,4-diazabicyclo[2.2.2]octane and a fast mixing accessible flow reactor (Comet X-01). Enal 9 was efficiently prepared by a partial reduction of the α, β-unsaturated ester 8 using diisobutylaluminium hydride in the flow system, and the continuous-flow diastereoselective aldol reaction was performed at low temperature, giving a good yield and diastereoselectivity of the desired aldol 10.