Lewis acid-mediated ring expansion

A Lewis-acid-mediated ring expansion of isobenzofuranones 1154 provides the final step during the total synthesis of naturally occurring ( )-3-aryl-8-hydroxydihydroisocoumarins 1155 (Equation 446) <2001J(P1)3017>. 

Type of reaction C-C bond formation Reaction conditions Dichloromethane, room temperature Synthetic strategy Lewis acid-mediated ring expansion Catalyst Titanium chloride (TiCl4)... 

Huang, X., Su, C., Liu, Q., and Song, Y. (2008). A facUe access to medium- and large-size naphthalenacarbo-cycles via Lewis acid mediated ring-expansion reaction of bicycUc vinyhdenecyclopropanes. Syrdett, 229-232. 

SCHEME 18.20 [4+2] Cycloaddition followed by a Lewis acid-mediated ring expansion. 

Many additional applications of semipinacol rearrangements on a-hydroxy epoxides have been developed,and these reactions have found use in complex molecule synthesis. For example, a-hydroxy epoxide 47 underwent a Lewis acid-mediated semipinacol ring expansion to set the challenging in-out intrabridgehead stereochemistry of the ingenol core. ... 

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