| 摘要 |
The present invention relates to a method for the preparation of a compound of formula (I),
wherein R 1 is different to R 2 ; R 3 is different to R 4 ; and R 1 , R 2 , R 3 and R 4 are each a moiety other than hydrogen, which method comprises,
i) photoirradiating at an intensity above ambient intensity a solution comprising a compound of formula (II),
wherein R 1 , R 2 , R 3 and R 4 are as defined above, to form a solution of a mixture of compounds of formula (IIa) and (IIb),
wherein R 1 , R 2 , R 3 and R 4 are as defined above; and
ii) contacting the mixture of compounds (IIa) and (IIb) with a hydrogen donating agent in the presence of an asymmetric hydrogenation catalyst, after initiation of i) and before termination of i).
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