Abstract
The coupling reactions mediated by sp-sp transition metals, mostly Pd, allowed the chemoselective preparation of some synthetic compounds and intermediate structures of great complexity. This work describes the methodology used to obtain several derivatives with bisoxazole and thiazole-oxazole units. The required organozinc reagents were prepared from nBuLi and ZnCl2, and the bimetallic derivative of ethyl oxazole-4-carboxylate was obtained by a second transmetalation with CuI.
Highlights
In recent decades, some marine natural products have been found to be an important source of new bioactive compounds and drug leads
The initial studies performed were based on the methodology reported by Hodges et al.[7]. These authors described that metalation of the oxazole with n-butyllithium leading to the formation of 2% of oxazole substituted at the 2 position and 20% of the product at the 4 position of the ring
The preparation of 4-(tributylstannyl)oxazole, 4-bromooxazole and oxazole-4-boronic acid were unsuccessful.[21]. It was tested a direct oxidative cross-coupling reaction catalized by Pd(0) between 2,4-dibromothiazole and oxazole
Summary
Some marine natural products have been found to be an important source of new bioactive compounds and drug leads. Zinc-derivative 1 was obtained by reaction of oxazole with n-BuLi, followed by in situ addition of solid ZnCl2 in anhydrous THF at -78 oC for 30 min. The reactivity of oxazole derivative 1 was tested for cross-coupling with triflate 4.22 The reaction using Pd (0) as catalyst in THF at reflux temperature afforded 5 in a 51% yield (Scheme 1).
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