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Diastereoselective Conjugate Additions to π-Allylmolybdenum Complexes:  A Stereocontrolled Route to 3,4,5-Trisubstituted γ-Butyrolactones

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journal contribution
posted on 11.05.2002 by Anthony J. Pearson, Eugen F. Mesaros
π-Allylmolybdenum complex 6b is obtained as a single isomer by Knoevenagel condensation of aldehyde 1 with Meldrum's acid. Conjugate additions of Grignard reagents to Meldrum's acid alkylidene derivative 6b are shown to be completely diastereoselective. Further functional group transformation of the 1,4-adducts, followed by demetalation, leads to trisubstituted tetrahydrofurans and γ-butyrolactones. Whereas the synthesis of tetrahydrofurans (X = 2H) is not completely stereoselective, the γ-butyrolactones (X = O) are obtained with good to excellent diastereoselectivities.