An efficient synthesis of the enantiomerically pure cisannulated cyclopentenes 2 and ent-2 was established by the use of an enzymatic transesterification and hydrolysis, respectively, followed by an S N 2-type substitution with a benzyloxymethyl cuprate and a sigmatropic rearrangement. The advantage of this approach is the short sequence combined with an excellent overall yield and an enantiomeric excess of 99%.
The concept of modern crop protection demands for a continuous supply of new or modified established pesticides to avoid the development of serious resistances. Recent reports on the insecticidal spinosyns 1 and 2 show that also this class of pest managing agents is increasingly exposed to the formation of resistances. The synthesis of new derivatives is therefore highly desirable. We describe in this paper a convergent approach towards novel enantiopure spinosyn A analogues of type 3, which is based on investigations of structure-activity relationships and employs a twofold Heck reaction as key step for the preparation of the tricyclic backbone assembly.
Aromatic amides 4 (3-aroyl-2,2,4,4-tetramethyloxazolidines or TMO amides) derived by acylation of 2,2,4,4-tetramethyloxazolidine 6 undergo ortho-and lateral lithiation reactions. Given sufficient steric hindrance to bond rotation, they exhibit atropisomerism about the Ar-CO bond and the Ar-CO axis is able to control the atroposelective formation of new stereogenic centres. Unlike amides derived from hindered secondary amines such as diisopropylamine, the 3-aroyl-2,2,4,4-tetramethyloxazolidines are acid-sensitive, and treatment with methanesulfonic acid gives lactones or lactams by cyclisation onto the amide group.
New spinosyn analogues 3 with an arene group as ring A and containing a L‐rhamnose moiety have been prepared. The key step in the synthesis of 3 is a Pd‐catalyzed twofold Heck reaction of glycosylated bromoarene 4, containing an iodovinyl side chain and a tri‐O‐methyl‐L‐rhamnose moiety with the cyclopentene‐annulated macrolactone 5. Compounds 3 may be of interest as new insecticides.
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