could be reused to afford the product in equal yield and
enantioselectivity (Table 2, entry 2). This makes the cost of
the chiral catalyst irrelevant.
Scheme 1. Application to the Steroid Side-Chain Synthesis
It is noteworthy that the chiral steroidal aldehyde 8 was
allylated to give 9 with high enantioselectivity (22S:22R )
96:4) (Scheme 1). Furthermore, the reaction was highly
chemoselective, reacting only with the aldehyde functionality.
No reaction was observed with the enone functionality in
the A ring. Interestingly, the use of (R)-i-PrPYBOX (6)
afforded the 22S-product as a single isomer (22S:22R )
100:0).
In conclusion, we have developed a highly catalytic
enantioselective allylation of aldehydes to give enantiomeri-
cally enriched homoallylic alcohols in good yields and
excellent enantiomeric excess in the presence of a catalytic
amount of In(OTf) -PYBOX complexes. Further work on
3
(
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Acknowledgment. We thank the National University of
Singapore and the National Natural Science Foundation of
China (no. 20472062) for providing the research funding.
We are also grateful to Medicinal Chemistry Program
(R-143-600-600-712) for financial support.
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Supporting Information Available: Experimental de-
tails, characterization data, and stereochemical proofs. This
material is available free of charge via the Internet at
http://pubs.acs.org.
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