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Stereocontrolled asymmetric synthesis of syn-E-1,4-diol-2-enes using allyl boronates and its application in the total synthesis of solandelactone F†
Anna Robinson,Varinder K. Aggarwal
Organic & Biomolecular Chemistry Pub Date : 01/18/2012 00:00:00 , DOI:10.1039/C2OB06975J
Abstract

The solandelactones A–H comprise a novel class of oxygenated fatty acids bearing an eight-membered lactone, transcyclopropane, and a 2-ene-1,4-diol subunit. The relative stereochemistry of the 1,4-diol subunit is anti in solandelactones A, C, E & G, and syn in solandelactones B, D, F & H. Having prepared one member of the solandelactones bearing anti stereochemistry (solandelactone E), we have targeted the syn series and developed methodology for the synthesis of enantioenriched syn-2-ene-1,4-diols. The methodology comprises asymmetric deprotonation of an alkyl 2,4,6-triisopropylbenzoate using sBuLi/sparteine, followed by addition of the α-lithiobenzoate to β-silyl vinyl boronic acid ethylene glycol ester. The boron-ate complex generated undergoes a 1,2-metallate rearrangement furnishing an intermediate allyl boronic ester which is trapped by an aldehyde in the presence of MgBr2 to furnish anti-β-hydroxyE-allylsilanes in good yields, high diastereoselectivity and high enantioselectivity. These sensitive products were oxidized using mCPBA to the corresponding epoxides and subsequently treated with acid to furnish syn-E-2-ene-1,4-diols (∼4 : 1 d.r.). Application of the methodology to appropriately functionalized aldehyde and ω-alkenyl 2,4,6-triisopropylbenzoate coupling partners, led to a short, highly selective route to solandelactone F (bearing a syn-E-2-ene-1,4-diol).

Graphical abstract: Stereocontrolled asymmetric synthesis of syn-E-1,4-diol-2-enes using allyl boronates and its application in the total synthesis of solandelactone F
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