Alkylated polystyrene-supported sulfonic acid

Pt-catalyzed hydration of various aliphatic and aromatic alkynes under phase transfer conditions in (CH2C1)2/H20 in the presence of Aliquat 336 led to either a Markovnikov product, mixtures of two ketones, or ketones with the carbonyl group positioned away from the bulky side.72 In the absence of the phase transfer reagent, Aliquat 336, hardly any reaction took place. Recently, a hydrophobic, low-loading and alkylated polystyrene-supported sulfonic acid (LL-ALPS-SO3H) has also been developed for the hydration of terminal alkynes in pure water, leading to ketones as the product.73 Under microwave irradiation, the hydration of terminal arylalkynes was reported to proceed in superheated water (200°C) without any catalysts.74... 

Low-loading alkylated polystyrene-supported sulfonic acid, water, 40°C, 12-24 h, 76-94% yield. A tertiary TBDMS ether was not cleaved. A TBDMS can be cleaved in the presence of a TBDPS ether. TIPS, TBDPS, OTr, OMOM ethers, and an acetate can all be cleaved, but the authors do not indicate relative rates... 

Furthermore, low-loading (e.g. 0.17 mmol/g) and alkylated polystyrene-supported sulfonic acid (LL-ALPSSO3H) such as 13 successfully calatyzed deprotection of tert-butyldimethylsilyl- (TBS) protected alcohols in water without using organic cosolvents (Scheme 3.38). 

Only a few examples of solid-phase syntheses of phosphonic, phosphoric, and sulfonic acids have been reported (Figure 3.16). Benzyl esters of these strong acids can act as alkylating agents, and may therefore be too labile to serve as linkers for long synthetic sequences on solid phase. However, if cross-linked polystyrene is used as the support, the reactivity of, for example, benzyl sulfonates is strongly reduced, and even... 

The pioneer work in this field was carried out on polystyrene-supported acid catalysts [161]. Thereafter, several works on the use of sulfonic, strong acidic cation exchangers as acid catalysts were reported for alkylation, hydration, etherification, esterification, cleavage of ether bonds, dehydration, and aldol condensation [162,168-171], Besides, industrial applications of these materials were evaluated with reactions related to the chemistry of alkenes, that is, alkylation, isomerization, oligomerization, and acylation. [163,169], Also, Nation, an acid resin which has an acid strength equivalent to concentrated sulfuric acid, can be applied as an acid catalyst. It is used for the alkylation of aromatics with olefins in the liquid or gas phases and other reactions however, due to its low surface area, the Nation resin has relatively low catalytic activity in gas-phase reactions or liquid-phase processes where a nonpolar reactant or solvent is employed [166],... 

Because of the special structural requirements of the resin-bound substrate, this type of cleavage reaction lacks general applicability. Some of the few examples that have been reported are listed in Table 3.19. Lactones have also been obtained by acid-catalyzed lactonization of resin-bound 4-hydroxy or 3-oxiranyl carboxylic acids [399]. Treatment of polystyrene-bound cyclic acetals with Jones reagent also leads to the release of lactones into solution (Entry 5, Table 3.19). Resin-bound benzylic aryl or alkyl carbonates have been converted into esters by treatment with acyl halides and Lewis acids (Entry 6, Table 3.19). Similarly, alcohols bound to insoluble supports as benzyl ethers can be cleaved from the support and simultaneously converted into esters by treatment with acyl halides [400]. Esters have also been prepared by treatment of carboxylic acids with an excess of polystyrene-bound triazenes here, diazo-nium salts are released into solution, which serve to O-alkylate the acid (Entry 7, Table 3.19). This strategy can also be used to prepare sulfonates [401]. 

In an opposite manner to bases such as 1 and 2 in terms of reactivity, polymer-supported tosyl chloride equivalent 14 is able to capture alcohols as polymer-bound sulfonates 15, which are released as secondary amines, sulfides and alkylated imidazoles with primary amines, thiols and imidazoles as nucleophiles in a substitution process (Scheme 6) [24]. This technique has further been extended for the preparation of tertiary amines [25] and esters [26]. Excess of amine was scavenged by polymer-supported isocyanate 16 [27, 28] while excess of carboxylic acid was removed by treatment with aminomethylated polystyrene 17. 

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