No abstract

Treatment of 1,4-dimethoxynaphthalenes with iodosobenzene diacetate and trimethylsilyl chloride or bromide furnished the haloacetoxylated, acetoxylated, and halogenated 1,4-dimethoxynaphthalenes in excellent yield. The reaction pathway for each transformation was shown to be a function of reagent stoichiometry. A mechanistic hypothesis is presented that rationalizes the reaction pathways and explains the subtle differences in the halogenation reactions. The acetoxylation, for example, is thought to involve the formation of an iodonium ion that promotes the nucleophilic addition of acetate ion and subsequent 1,2-acetyl migration. Bromination occurs as a direct result of the oxidation of trimethylsilyl bromide to bromine, followed by electrophilic aromatic substitution. Chlorination is thought to proceed via a radical process and not the formation of molecular chlorine from the dissociation of iodosobenzene dichloride. The haloacetoxylation reaction also appears to be fairly specific for 1,4-dimethoxynaphthalenes, since the analogous reaction with a 1,4-dimethoxybenzene derivative was unsuccessful.

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The enantiospecific and regioselective rhodium-catalyzed allylic alkylation of a series of chiral nonracemic allylic carbonates, followed by ozonolysis and reductive lactonization, provides a convenient route to optically active gamma-lactones. Sequential alkylation and reductive alkylation furnished the alpha-quaternary-beta-ternary substituted gamma-lactone derivative as a >/=10:1 mixture of diastereoisomers.

Cyclic ether containing natural products represent important synthetic targets owing to their unique structural and biological properties. 1 The development of new methodology for the synthesis of this ubiquitous class of compounds has been the focus of extensive investigation for the last 20 years. However, the development of new and general methods capable of accessing this class of compounds continues to dominate this area of investigation. 2 A number of radical methods 3-5 have recently been developed for the stereoselective synthesis of cyclic ethers. Methods that utilize acyl radicals 6 have, however, not been forthcoming. In this paper, we describe the first example of the intramolecular addition of an acyl radical to a vinylogous carbonate for the efficient and stereoselective construction of 5-, 6-, and 7-membered cyclic ethers (eq 1). 7