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2005
Furan derivatives
R 0060
Stereoselective Synthesis of Highly Substituted Bicyclic γ-Lactones Using HomoAddition of 1-(1-Cycloalkenyl)methyl Carbamates. — Key step of the stereo07- 091 aldol
selective synthesis of bicyclic lactones is the stereoselective addition of aldehydes (II)
towards metalated cycloalkenylmethyl carbamates (I), (VI) or (IX) to give the corresponding adducts in excellent diastereoselectivity (>95% ds.). Use of (-)-sparteine in
the lithiation step provides an asymmetric variant of this reaction. In this case, moderate
to good enantioselectivities but lower yields [cf. (III)] are achieved. Mercury-catalyzed
methanolysis followed by Grieco oxidation of the adducts then affords the poly-substituted bicyclic lactones (IV), (VIII) and (XI), respectively. The stereoselectivities
achieved for substrates with cycloalkenyl rings with more than 6 members [cf. (XIV)]
are only moderate. — (OEZLUEGEDIK, M.; KRISTENSEN, J.; REUBER, J.;
FROEHLICH, R.; HOPPE*, D.; Synthesis 2004, 14, 2303-2316; Org.-Chem. Inst.,
Westfael. Wilhelms Univ., D-48149 Muenster, Germany; Eng.) — Mischke
2005
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