Acyl sulfonates, cleavage

The dicyclopentadienyl metal compounds undergo Friedel-Crafts alkylation and acylation, sulfonation, metalation, arylation, and formyla-tion in the case of ferrocene, dicyclopentadienyl ruthenium, and dicyclopentadienyl osmium, whereas the others are unstable to such reactions ( ). Competition experiments (128) gave the order of electrophilic reactivity as ferrocene > ruthenocene > osmocene and the reverse for nucleophilic substitution of the first two by n-butyl lithium. A similar rate sequence applies to the acid-catalysed cleavage of the cyclopentadienyl silicon bonds in trimethylsilylferrocene and related compounds (129), a process known to occur by electrophilic substitution for aryl-silicon bonds (130). 

Oxidative Cleavage. Once the desired stereochemistry is obtained, the phenyl sulfone serves its final purpose during oxidative cleavage using ozone. The immediate product formed is presumably an acyl sulfone which can be converted to an ester (eq 6) or an amide (eq 7). In the absence of an external nucleophile, an internal alcohol can be used to form a lactone (eq 8). ... 

Synthesis of Butenolides/Butyroactones Using Mg/HgClx for Sulfone Cleavage. Sheng et al. have reported the synthesis of butenolides and butyroactones using the sulfone-bound resin 140 (Scheme 12.31)." ° The procedure for the synthesis of butenolides/butyroactones involved the 5-alkylation of lithiophenylsulhnate resin 79, followed by sulfonyl anion alkylation with an epoxide to yield 45. Subsequent acylation... 

In these compounds the following substituents can be present alkyl,alkenyl,aryl, halogen,sulfonic acid, amino, hydroxyalkyl, acyl, and carboxyl. The cleavages of 5,5 - (109) and 3,5 -diisoxazolyl (111) proceed similarly both isoxazole rings are cleaved in the former (109—> 110). ... 

Among other methods for the preparation of alkylated ketones are (1) the Stork enamine reaction (12-18), (2) the acetoacetic ester synthesis (10-104), (3) alkylation of p-keto sulfones or sulfoxides (10-104), (4) acylation of CH3SOCH2 followed by reductive cleavage (10-119), (5) treatment of a-halo ketones with lithium dialkyl-copper reagents (10-94), and (6) treatment of a-halo ketones with trialkylboranes (10-109). 

Decarbonylation of acyl halides 7-20 Cleavage of Michael adducts 7-21 Deoxygenation of vic-diols 7-22 Cleavage of cyclic thionocarbonates 7-23 Deoxidation of epoxides 7-24 Desulfurization of episulfides 7-25 Reaction of a-halo sulfones with bases (Ramberg-Backlund)... 

Furthermore, the cleavage of organic sulfites and sulfates by hydrogen fluoride gives the corresponding alkyl or acyl fluorides in fair to good yield,287 e.g. formation of acetyl fluoride from the mixed anhydride287 or sulfonyl fluorides from sulfonic acid anhydrides.287... 

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]. 

The resin-bound perfluoroalkylsulfonyl linker is compatible with many common solid-phase reactions, such as tin dichloride-mediated aromatic nitro group reduction, trifluoroacetic acid-mediated tBoc deprotection, reductive amination reactions, acylation, and sulfonation. It is possible to perform several sequential synthetic reactions on the nonflate resin so that multistep syntheses can be carried out. The solid-phase approach provides an operationally simple, inexpensive, and general protocol for the cleavage... 

A mechanistic rational for the ionization of pyrrole-3-triflates 72 was proposed as shown below (Eq. 8). Heterolytic cleavage of the sulfonate ester bond, assisted by donation of the nitrogen lone pair, results in loss of the triflinate ion59 and gives rise to the C-acyl iminium ion intermediate 73. This process is further facilitated by the stabilizing effect of a... 

The anion derived from sulfone 4 coupled readily to aldehyde 3 (Scheme 17.7) to give a mixture of P hydroxysulfones that could be converted to a 2.5 1 mixture of the olefins 2 and 32, after acylation and reductive desulfonylation. Unfortunately, problems were subsequently encountered during the attempted removal of the acetal unit from 2 and 32 with pyridinium p-toluenesulfonate in propanol and acetonitrile. Apparently, silyl ether cleavage competed with the desired deacetalation process. Notwithstanding this, the C(24),C(26) diol was isolated pure in 33% yield, along with 28% yield of recovered starting material. This diol... 

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],... 

In carboxylates, we remember, attack generally occurs at acyl carbon, and in sulfonates, at alkyl carbon, with a resulting difference in point of cleavage. In... 

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