Diels-Alder reaction 10-camphorsulfonic acid

Diels-Alder reactions and cyclocondensations. Tricyclic skeletons containing up to 5 stereocenters are created by this method in an intramolecular Diels-Alder re-Camphorsulfonic acid is also present as a catalyst. The Danishefsky cyclocondensation involving an aldehyde and a very reactive diene is also similarly catalyzed. ... 

An interesting phenomenon has been observed in the high pressure Diels-Alder reactions of the l-oxa[4.4.4]propella-5,7-diene (117) with 1,4-naphthoquinone, maleic anhydride and N-phenylmaleimide, where the diene 117 undergoes a rearrangement to the diene isomer 118 which, although thermodynamically less favored, exhibits a greater reactivity [40]. The reactivities of the three dienophiles differed since maleic anhydride and N-phenylmaleimide reacted only in the presence of diisopropylethylamine (DIEA) and camphorsulfonic acid (CSA), respectively (Scheme 5.15). The distribution of the adduct pairs shows that the oxygen atom does not exert a consistent oriental dominance on TT-facial selectivity. 

LP-DE also promotes and accelerates intramolecular Diels-Alder reactions of low reactive polyenones. The use of a catalytic amount of camphorsulfonic acid (CSA) further accelerates the cycloaddition and enhances the diastereo-selectivity [41]. Table 6.7 illustrates the effect of CSA on the intramolecular Diels-Alder reaction of 2-methyl-l,7,9-decatrien-3-one. 

The retrosynthesis of this compound by Batey and co-workers [96] recognized that the unprecedented hexahydropyrrolo[3,2-c]quinoline core could be synthesized using a three-component Pavarov hetero-Diels-Alder reaction [97]. For this synthetic strategy to be successful, however, reaction conditions that favor the exo approach of the dienophile over the endo approach had to be found. For this purpose, a variety of protic acids were tested, and it was found that the reaction was best carried out in the presence of camphorsulfonic acid (CSA). Indeed, a mixture of 4-aminobenzoate 200 and N-Cbz 2-pyrroline 201 were stirred at room temperature in the presence of catalytic CSA to afford exo cyclo-adduct 203 as the major product (Scheme 12.28). The N-Cbz 2-pyrroline served as both an aldehyde equivalent and a dienophile in this context. The Diels-Alder adduct 203 already bore all the requisite functionalities for the successful completion of the synthesis, which was achieved in six additional steps. 

Asymmetric Dieh-Alder Reactions. The commercial availability of either enantiomer of camphorsulfonic acid has made it quite useful in asymmetric Diels-Alder reactions. Reaction of the sultone (generated from CS A) with Lithium Diisopropylamide followed by esterification and (3-elimination yields the crystalline acrylate (eq 14). The Lewis acid-catalyzed [4 + 2] cycloaddition of 1,3-dienes with this acrylate affords the corresponding scalemic adduct which can be reduced with Lithium Aluminum Hydride to yield an enantiomerically pure alcohol (eq 15). ... 

Electrophilic substitution of indole. acidity of the LiC104-Et20 system. It can Diels-Alder reactions and cyclocond up to S stereocenters are created by this m action. Camphorsulfonic acid is also pm condensation involving an aldehyde and catalyzed. ... 

In 2012, Fukuyama s group reported a novel synthesis route to the spiro-p-lactonic sesquiterpene (-)-anisatin, and they also relied on the construction of a bicyclo[2.2.2]octane system via a DIB-mediated methoxylative phenol dearomatization followed by an intramolecular Diels-Alder reaction [127]. The homochiral phenolic dihydrobenzofuran propargyl ether 231 thus afforded, via the ort/io-quinone monoketal 232 and treatment of its intramolecular [4+2] epimeric cycloadducts with camphorsulfonic acid in MeOH, the bicyclo[2.2.2] octanedienone 234 as a single diastereomer (Fig. 56). Further transformation of 234 gave the vinyl 235, whose trisubstituted double btmd bridge was oxidatively cleaved by mild ozonolysis to furnish the ketoaldehyde 236, en route to (-)-anisatin [127]. 

An important strategy for achieving substrate control is the use of chiral auxiliaries, which are structures incorporated into reactants for the purpose of influencing the stereochemistry. Two of the most widely used systems are oxazolidinones " derived from amino acids and sultams derived from camphorsulfonic acid. These groups are most often used as carboxylic acid amides. They can control facial stereoselectivity in reactions such as enolate alkylation, aldol addition, and Diels-Alder cycloadditions, among others. The substituents on the chiral auxiliary determine the preferred direction of approach. 

---