A highly practical method for the enantioselective allylation of acylhydrazones has been developed. The previously reported strained silacycle reagent 1 reacts with a wide variety of acylhydrazones to give the hydrazide products with good enantioselectivity (83-89% ee, typically). It has been demonstrated that the products may be isolated without chromatography by recrystallization in >/=98% ee.
An efficient synthesis of the C(1)–C(9) fragment of fludelone has been developed. The key step is a tandem silylformylation-crotylsilylation/Tamao oxidation sequence that establishes the C(5) ketone, the C(6), C(7), and C(8) stereocenters, and the C(9) alkene in a single operation from a readily accessed starting material. The stereochemical outcome at C(6) depends critically on the development of an “aprotic” Tamao oxidation, which leads to a reversal in the intrinsic diastereoselectivity observed using “standard” Tamao oxidation conditions.
[Structure: see text] Phenols are effective directing and activating groups for our allylchlorosilane reagents, allowing the highly enantioselective allylation of a range of 2-aminophenol-derived aldimines. When the phenol is incorporated into the substrate ketimines may be allylated highly enantioselectively, leading to the experimentally simple synthesis of a range of tertiary carbinamine structures.
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