Abstract
The addition of racemic titanated alkynyl N,N -diisopropylcarbamates onto enantiopure α-dibenzylamino- or α-silyloxyalkanals affords
two (out of four possible) diastereomeric, enantiopure 5-hetero-substituted 4-hydroxy-1,2-alkadienyl
carbamates. As demonstrated for hydroxyallenes 23 and 24 , the reaction sequence for modified Nazarov cyclization according to Tius, yields
stereohomogeneous, highly substituted 5-alkylidene-2,3-dialkyl-4-phenyl-2-cyclopenten-1-ones
(Z,R )-25 and (E,R )-26 .
Key words
diastereoselectivity - allenes - Nazarov reactions - carbamates - cyclizations - cyclopentenones
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Yields of compound (Z,R )-25 and (Z,R )-26 are based on enone 20a .