PubMed · 8747005
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W Forest. 1995. What's in a name?. https://doi.org/10.1289/ehp.951031080a
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[Structure: see text] A strategically novel approach to the formation of syn-1,3-diol mono- and diethers through electrophilic activation of homoallylic alkoxymethyl ethers has been developed. The resulting polyketide-like synthetic fragments are generated in good yield and with excellent stereocontrol. A chairlike transition state is proposed to account for the high stereoselectivity. Varying the conditions of the reaction workup results in the efficient generation of mono- and diether containing structural units common to polyketide natural products.
[reaction: see text] The (1-naphthyl)propargyl group is introduced as a sterically unobtrusive alcohol protecting group that is cleaved in a single step by exposure to dichlorodicyanoquinone in wet dichloromethane. In conjunction with the 4,6-O-benzylidene protecting group, and the use of the sulfoxide glycosylation method, 3-O-naphthylpropargyl-protected mannosyl donors are extremely beta-selective.
Iodonium ylides, generated in situ with bisacetoxyiodobenzene, are converted to allyl- or benzyl-substituted oxonium or sulfonium ylides via rhodium- or copper-catalyzed carbene transfer. Except for the S-benzyl example, the resulting ylides undergo rearrangement to the corresponding 2-substituted heterocycles. This demonstrates the first use of iodonium ylides as diazoketone surrogates for the generation and rearrangement of onium ylide intermediates. This abbreviated one-step method proceeds in comparable yields relative to the corresponding two-step route employing diazoketone intermediates.