Previously attempted spirocyclizations to form the ABCD ring system of azaspiracid (1) have proven unsuccessful owing to the anomeric effects that favor the formation of the undesired 13S diastereomer. By the use of a hydrogen bond donor as an auxiliary group, such anomeric effects were successfully overcome. Thus, the first synthesis of the ABCD ring system of azaspiracid with the proper 13R configuration of the C13 stereocenter was achieved.
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Nicolaou et al. (2001) studied this question.
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