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キーワード:
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要旨:
The sense of 1,3-asymmetric induction in the TiCl4 mediated allylailane addition of O-(allyl)silyl protected aldehydes 14 is opposite (>62;90% syn selectivity) to that of the previously reported reaction of the 0-benzyl protected analogs 7 with allyltrimethylsilane (90% anti selectivity). Crossover experiments show that strict intramolecularity pertains, suggesting an intramolecular allylsilane addition as depicted in 15. Surprisingly, the switch from TiCl4 to SnCl4 results in the reversal of diastereofacial selectivity and in an intermolecular allyl transfer mechanism. α-Chiral β-silyloxy aldehydes of the type 35 are not very well suited for stereoselective allylations.
