Beckwith ring expansion

Radical-mediated ring expansion of 2-halomethyl cycloalkanones. 

Name Reactions A Collection of Detailed Mechanisms and Synthetic Applications, DOI 10.1007/978-3-319-03979-4 93, Springer International Publishing Switzerland 2014 

The Dudley reagents are employed for the protection of alcohols as benzyl or PMB ethers, respectively, under mild conditions. Carboxylic acids are readily protected as well. Activation of the appropriate Dudley reagent in the presence of an alcohol furnishes the desired aiylmethyl ether. The benzyl reagent is activated upon warming to approximately 80-85 °C, whereas activation of the PMB reagent occurs at room temperature upon treatment with methyl triflate (CHsOTf) or protic acid. Aromatic solvents, most commonly trifluorotoluene, often provide the best results. Magnesium oxide (MgO) is typically included in the reaction mixture as an acid scavenger. For benzylation of carboxylic acids, triethylamine (EtsN) is used in place of MgO.  

The Dudley reagents are conveniently prepared from readily available starting materials and are indefinitely stable to storage and handling under standard laboratory conditions. Alternatively, both reagents are corrrmercially available. 

Benzylation of a monoacetylated diol is shown in Exarrple 1. The Dudley benzyl reagent was tmiquely effective for protection of the free alcohol without loss and/or migration of the labile acetyl group. 

Beckwith, A. L. J. O Shea, D. M. Gerba, S. Westwood, S. W. J. Chem. Soc., Chem. Commun. 1987, 666. Athelstan L. J. Beckwith is a professor at University of Adelaide, Adelaide, Australia. 

Name Reactions, 4th ed., DOI 10.1007/978-3-642-01053-8 86, Springer-Verlag Berlin Heidelberg 2009 

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The factors that effect the partition of a radical (resulting from reaction of the halide precursor with AIBN-BusSnH) between three-carbon Dowd-Beckwith ring expansion... 

Other references related to the Dowd-Beckwith ring expansion are cited in the literature. ... 

Beckwith (see Dowd-Beckwith Ring Expansion Reaction) Belleau (see Fujimoto-Belleau Reaction)... 

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