Demand-Based Thiolate Anion Generation under Virtually Neutral Conditions:  Influence of Steric and Electronic Factors on Chemo- and Regioselective Cleavage of Aryl Alkyl Ethers

Abstract

Thiolate anions have been generated in a "demand-based" fashion under virtually neutral conditions for chemoselective deprotection of aryl alkyl ethers. Solvents play the critical role in making the reaction effective and should have high values of epsilon (>30), molecular polarizabilities (>10), and DN (>27) and low values of AN (<14). However, it is the combined effect of all of these physical properties that make a particular solvent effective. The reaction rates of cleavage of various aryl alkyl ethers are dependent on the steric crowding around the O-alkyl carbon and follow the order propargyl approximately allyl approximately benzyl > methyl > ethyl. Electron-withdrawing substituents increase the rate of ether cleavage reaction. The influence of the steric and electronic factors have been successfully exploited for selective deprotection of aryl alkyl ethers during inter- and intramolecular competitions.

Synthesis and NMR Spectroscopic Study of the Self‐Aggregation of 2‐Substituted Benz­ene‐1,3,5‐tricarboxamides

“…The 2‐methoxy‐benzamides 5 and 6 were deprotected by nucleophilic methyl ether cleavage according to the conditions reported by Chakraborti et al,26 employing the potassium salt of thiophenol in N ‐methyl‐2‐pyrrolidone at 150 °C. The final alkylation step of the phenol derivatives 7 and 8 was found to be a difficult transformation.…”

Synthesis and liquid crystal properties of triphenylene liquid crystals bearing polymerisable acrylate and methacrylate groups

“…Regioisomerically pure triphenylenes bearing four hexyloxy substituents and two methoxy groups were synthesised either from the corresponding o-terphenyl (itself prepared by palladium-catalysed Suzuki-Miyaura coupling) [37,38] or via the oxidative cyclisation between a tetraalkoxybiphenyl (also prepared by palladiumcatalysed Suzuki-Miyaura coupling) and the appropriate dialkoxybenzene [21,39,40]. A number of methods are available for the selective cleavage of methyl ethers, but we found treatment of the Liquid Crystals 945 dimethoxy triphenylenes with thiophenol/potassium carbonate in dimethylformamide (DMF) to be the best method in all cases [41,42].…”

2‐Arylhydroxynitroindoles: A new procedure for the cleavage of aryl methyl ethers

“…The ether bond cleavage techniques with the use of AlCl 3 [6], BBr 3 [7], and PhSH in the presence of K 2 CO 3 [8], HBr [9], and (CH 3 ) 3 SiI [10] described in literature failed. Either resinification occurred or the reaction did not run at all.…”