TETRAHEDRON LE'Iq'ERS Pergamon Tetrahedron Letters40 (1999) 8121-8124 Highly selective cleavage of prenyl ethers by means of a TiC14-n-BunNI mixed reagent Takayuki Tsuritani, Hiroshi Shinokubo and Koichiro Oshima * Department of Material Chemistry, Graduate School of Engineering, Kyoto University, Yoshida, Sakyo-ku, Kyoto 606-8501 Japan Received 19 July 1999; revised 1 September 1999; accepted 3 September 1999 Abstract Treatment of the prenyl ether of ethyl salicylate with a TiCI4-n-Bu4NI mixed reagent resulted in cleavage of the C-O bond to provide ethyl salicylate in quantitative yield. On the other hand, no cleavage reaction was observed when ethyl p-prenyloxybenzoate was used as a substrate. In this system, the cleavage reaction of ethers proved to be accelerated by the chelating effect of a neighboring group in the substrate. © 1999 Elsevier Science Ltd. All rights reserved. Keywords: deprotection;ethers; titanium;titaniumcompounds; ammoniumsalts. Selective removal of a protecting group has been important for organosynthetic methodology, l Among numerous deprotection methods, cleavage of the ether linkage is usually performed under basic condi- tions or by using Lewis acids (BBr32 or Me3SiI3). We have already reported the C-O bond cleavage reaction of epoxides using a titanium tetrachloride-tetrabutylammonium iodide mixed reagent to provide iodohydrin (Scheme 1).4 This reagent is readily prepared by mixing TiCI4 and n-BuaNI at 0°C. Here we wish to report that the TiCln-n-Bu4NI5 system cleaves prenyl ethers selectively in the presence of allyl or crotyl ethers. 6 OH R.~R TiCI4/n"Bu4NI ~ R.~R I Scheme 1. Treatment of tetrabutylammonium iodide (1.1 mmol) with TiCI4 (1.1 mmol) in dichloromethane at 0°C provided a dark-red solution. After being stirred for 10 min, an addition of the prenyl ether of 1- octanol (la, 1.0 mmol) afforded deprotected 1-0ctanol (2a) quantitatively (Scheme 2). No trace amount of 1-0ctanol was obtained when the corresponding allyl or methyl ether was used as a substrate under the * Corresponding author. 0040-4039199/$ - see frontmatter© 1999ElsevierScienceLtd. All rightsreserved. PII: S0040-4039(99)01717-7