Flow Friedel–Crafts alkylation of 1‐adamantanol with arenes using HO‐SAS as an immobilized acid catalyst

Abstract

In this communication flow Friedel-Crafts alkylation was studied using hydroxy-substituted sulfonic acid-functionalized silica as a catalyst and 1-adamantanol as a model substrate. The reaction of 1-adamantanol (1a) with toluene (2a) proceeded well with 5 min of residence time at 120 C to give good yield of 1-tolyladamantane (3a) as a 1:9 mixture of meta and para isomers. When the flow synthesis was carried out over 2.5 hr of running time, the collected five fractions contain the product 3a in 97-92% yields, suggesting the durability of the catalyst.

Greener Synthesis of Pristane by Flow Dehydrative Hydrogenation of Allylic Alcohol Using a Packed-Bed Reactor Charged by Pd/C as a Single Catalyst

“…When we used Pd/Al 2 O 3 instead of Pd/C, the reaction gave alcohol 4 in a 92% yield along with a trace amount of pristane 3 ( Table 1 , entry 2). These results strongly suggest that the Pd/C catalyst has an exceptional ability to reduce an allyl alcohol moiety to pristane 3 , which was consistent with results reported by other groups [ 10 , 11 , 12 , 13 , 14 , 15 ]. Under harsh conditions that included higher temperature (90 °C) and higher pressure (10 atm), the yield of 4 was increased, but that of 3 did not change ( Table 1 , entry 3).…”

“…Then, we focused on silica-supported sulfonic acids (SAS) [ 7 , 8 ], for the flow dehydration step. Consequently, we found that the use of hydroxy-functionalized sulfonic acid silica, HO-SAS [ 9 , 10 , 11 ], for flow-dehydration worked well. Combined with the flow hydrogenation using Pd/C, we completed an acid waste-free flow synthesis of pristane ( Scheme 1 ) [ 10 ].…”

Recent Advancements in Typical Friedel–Crafts Alkylation Reactions Focused on Targeting Arene Nucleophiles

“…[93][94][95] Ryu and co-workers used a flow technique for the FC arylation of alcohols using hydroxy-substituted sulfonic acid functionalized silica (HO-SAS) as a catalyst (Scheme 16). 96 With 5 minutes of residence time at 120 °C temperature, adamantan-1-ol and toluene were converted into 1tolyladamantane in excellent yields (m/p = 1:9). Furthermore, continuous-flow synthetic strategy, especially using packed bed reactors, yielded the desired materials in a green and sustainable way 97 and the development and commercialization of robust, highly active heterogeneous catalysts is a crucial task in this field of study.…”

Development of highly efficient Friedel–Crafts alkylations with alcohols using heterogeneous catalysts under continuous-flow conditions

“…Conversion was not determined for this substrate, due to overlap with the solvent peak under standard GC conditions. 1-Adamantanol, reportedly a good aliphatic substrate, 7 was found to be troublesome in our case, with rapid catalyst deactivation observed, especially at high temperatures; the desired 2k was isolated in only 26% yield after optimising the reaction conditions. Neopentyl alcohol gave no isolable amount of the desired product, which is presumably due to the instability of the primary carbocation intermediate.…”

“…Recent water-tolerant Lewis acid 3 and heterogeneous acid catalyst developments have enabled the catalytic conversions of activated alcohols (and aldehydes) with solvent amounts of arenes. 4 Supported iron oxide, 5 a fluorinated polymer-supported Brønsted acid, 6 and hydroxyl-functionalised sulfonic acid silica 7 were used as fixed bed catalysts to achieve continuous-flow reactions with considerably high turnover frequencies (TOFs).…”