Synthesis oxiranyllithiums

Capriati, V. Florio, S. Luisi, R. Russo, V. Sal-omone, A. Oxiranyllithium based synthesis of... 

Just as cyclopropyllithiums and aziridinyllithiums are highly configurationally stable, it is to be expected that lithiated oxiranes (those that are chemically stable44) also maintain their configuration.45 47 Townsend made use of oxiranyllithium 93 (which can be assumed to have configurational stability) in the synthesis of (+)-cerulenin 94 48... 

Reaction of the oxiranyllithium with aldehydes is also carried out by an in situ trapping method at very low temperatures in order to avoid decomposition of the reagent. Its applicability to a complex situation has been demonstrated in a synthesis of hemi-... 

An overview of oxiranyllithiums as chiral synthons for asymmetric synthesis discussed the generation of a-lithiated oxirane derivatives by various synthetic methods." The mechanism and stereochemical features in asymmetric deprotonafion... 

Reiterative application of this protocol has allowed the stere-ocontrolled construction of polytetrahydropyrans and polycyclic ethers containing six- and seven-membered rings (eq 5). Reaction of the oxiranyllithium with aldehydes is also carried out by an in situ trapping method at very low temperatures in order to avoid decomposition of the reagent. Its applicability to a complex situation has been demonstrated in a synthesis of hemibrevetoxin B (eq 6). It is noteworthy that deprotonation of 1 by n-BuLi is much faster than butyl addition to the aldehyde. 

In this manner, a flow reaction can have a short residence time, allowing the oxiranyllithium species 2, which is an unstable reactive species with a short lifetime, to react with methyl iodide before the species decomposes. In contrast, a batch reaction cannot be completed in a short reaction time due to the time for its conduction needed for the reaction. A batch reaction on an extremely small scale may be completed within a reaction time of 1 min or less, but a batch reaction on a large scale cannot be completed in a short time because the dropping of s-BuLi to a solution of 1 requires an additional time. Fast dropping in a batch reactor may cause rapid increase in the temperature which accelerates the decomposition of 2. Thus, flow microreactor synthesis can offer crucial advantages. 

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