2 + 21 Cycloaddition of (menthy1oxy)methylketene (2) to cis-ethyl propenyl ether showed a ca. 3:l diastereoselectivity. A two-step transformation of the thermodynamically more stable adduct 4 furnished the (2R*,3R*)compound 5 with ca. 50% e.e. (Scheme I). The analogous reaction sequence with cis-benzyl 1-hexenyl ether (9) and 2 showed a ca. 5.1 diastereoselectivity in 10 and 11 (Scheme 2). Absolute configuration of C(3) and C(4) in 11 has been proved by converting it to (-)-hlastmycinone. Accordingly, the preferred transition state has been deduced as 15.
8-Amino-7-aryl-6-halogen-substituted pyrido[2,3-b]pyrazines have been prepared as 6,6-biheterocyclic analogues of similarly substituted triazolopyrimidine fungicides. A concise four-step synthesis route has been worked out to prepare these novel compounds from commercially available starting materials. [(R)-(1,2-Dimethylpropyl)]-[6-fluoro-7-(2,4,6-trifluorophenyl)pyrido[2,3-b]pyrazin-8-yl]amine showed excellent activity against three economically important phytopathogens.
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