Enantiomerically enriched bicyclo[m.1.0]alk-3-en-2-ones possessing 8-, 12-, and 15-membered rings were prepared and subjected to additions of nucleophiles. 1,2-Additions of n-butyllithium were highly diastereoselective for all cyclopropyl enones examined. Reactions of (Z)-bicyclo[6.1.0]non-3-en-2-one and (E)-bicyclo[13.1.0]hexadec-3-en-2-one with dimethyloxosulfonium methylide were highly diastereoselective, while reaction of (E)-bicyclo[10.1.0]tridec-3-en-2-one with this reagent was not diastereoselective. In contrast, 1,4-additions of lithium diorganocuprates were highly diastereoselective for the 8- and 12-membered enones but were not diastereoselective for the 15-membered enone. All reactions were chemically efficient. The diastereoselectivities observed for 1,2-additions, which are thought to involve early transition states, can be rationalized by consideration of the low-energy conformations of each cyclopropyl enone. The diastereoselectivities observed for 1,4-additions, which may involve late transition states, do not correlate simply with the lowest energy conformations of these enones.
ASJC Scopus subject areas
- Organic Chemistry