Abstract
A versatile and metal-free approach for the synthesis of carbocycles and of heterocycles bearing seven- and eight-membered rings is described. The strategy is based on ring expansion of 1-vinylcycloalkanols (or the corresponding silyl or methyl ether) mediated by the hypervalent iodine reagent HTIB (PhI(OH)OTs). Reaction conditions can be easily adjusted to give ring expansion products bearing different functional groups. A route to medium-ring lactones was also developed.
Highlights
The presence of seven-membered rings in compounds with remarkable biological activity continuously challenges organic chemists to develop efficient method for their preparation [1,2,3,4,5,6,7,8,9,10,11,12,13,14]
The substrates required for the ring expansion reactions were prepared in an efficient manner
We found that treating 3e with HTIB in a mixture of AcOEt/MeOH gave 8e, in 67% yield (Entry 5)
Summary
The presence of seven-membered rings in compounds with remarkable biological activity continuously challenges organic chemists to develop efficient method for their preparation [1,2,3,4,5,6,7,8,9,10,11,12,13,14] (for examples of Molecules 2015, 20 natural or designed compounds, see Figure 1). Besides the palladium-catalyzed processes, other metal-mediated reactions were investigated and ring-closing metathesis and cycloadditions are probably the most used in the synthesis of seven- and eight-membered rings [5,6,7,8,9,10,12,16]. Another approach is a ring expansion reaction [12,17,18,19], which has the main advantage to avoid entropic factors and high-diluted conditions [1,15]. The ring expansion of methylene derivatives mediated by PhI(OH)OTs
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