Amide, sodium Diels-Alder reactions

Camphor-10-sulfonic acid (1) is available in large quantities in both enantiomeric forms. In only 3 steps the cyclic sulfonamide 2 (sultam) can be synthesized, which can be acylated with acid chlorides after deprotonation with sodium hydride (Scheme 1) [1, 2]. The resulting amides 3 are considerable more reactive towards nucleophiles than the corresponding carboxylic esters and the a,/ -unsaturated derivatives undergo, with excellent selectivities, Diels-Alder reactions or Michael additions under mild conditions. Al-... 

Keck and co-workers have shown that this Diels-Alder reaction offers promise for the synthesis of certain alkaloids and other nitrogen-containing products since the adducts are selectively cleaved to hydroxy amides by aluminum or sodium amalgam. 

Such a procedure has been exploited for the synthesis of several derivatives for which an anti-inflammatory activity has been claimed [58]. A derivative under study as the Histamine H3 antagonist was prepared by the thermal intramolecular Diels-Alder reaction of a triene derivative of buta-1,3-diene-1-sulfonic acid amide. 1,3-Butadiene sulfonamides 182 (a 67%, b 69%, c 99%, d 51%) were prepared by the base mediated condensation of M-Boc-methanesulfonamides (181) with a series of aldheydes. N-akylation of 182 to give trienes 183 (a 69%, b 76%, c 82%, d 59%) was achieved by reacting the sodium salts with allyl bromide in THF at reflux. The intramolecular Diels-Alder reactions of compounds 183 were performed at 145 °C in toluene in a sealed vessel under argon. Under these conditions compounds 184 and 184 were obtained in good yields (a 76% ratio 6 1, b 71% ratio 6 1, c 92% ratio 3 1, d 87% ratio 3 1). 

Successful polymer supported stereoselective Diels-Alder reaction was performed using immobilized enantiopure 4-(3-hydroxy-4,4-dimethyl-2-oxopyrro-lidin-l-yl)benzoic acid 12 as a chiral auxiliary [15]. The corresponding resin-bound acrylate derivate has been applied as the dienophile 13. Preparation of the precursor started with the combination of pantolactone 10 and the sodium salt of 4-aminobenzoic acid. Conversion into the corresponding benzyl ester followed. The obtained racemate was esterified with (lS)-camphanic acid chloride to a dia-stereomeric mixture to gain the enantiopure compounds by chromatographic separation. After subsequent saponification of the camphanic acid moiety and hydrolysis of the benzyl ester the (R)-enantiomer 11 was coupled to Rink amide resin (Scheme 12.6). 

This mechanism has been confirmed using isotopically labelled fluorobenzene. Benzynes have been trapped by dienes in Diels-Alder reactions. They can also be generated by strong bases such as sodium amide in liquid ammonia in this way bromobenzene can be used without the interference of metal-halogen exchange which is the preferred course with lithium alkyls. 

Density functional theory computational studies have been used to determine die importance of secondary orbital interactions for the stability of transition-state structures for die 4 + 2-cycloaddition of furan with cyclopropene.175 Kinetic studies of die 2 + 4-cycloaddition of 2-cyclopropylidene acetates with furan and dimethylful-vene suggest a mechanism involving diradicals or zwitterions as intermediates.176 Cyclopropene, produced by die reaction of allyl chloride with sodium bis(bimediyl-silyl)amide, reacts with 1,3-diphenylisobenzofuran to produce both endo- and exo-Diels-Alder cycloadducts isolated for the first tune.177... 

A variety of diverse synthetic methods have been empioyed for the preparation of cyclopropane (1 j. Schlatter and Demjanov and Dojarenko pyrolyzed cyclopropyltrimethylammonium hydroxide at 320°C using platinized asbestos as the catalyst. About equal amounts of cyclopropene (1) and cyclopropyidimethylamine are formed, contaminated with some dimethyl ether and ethylene. Treatment with dilute hydrochloric acid removed the amine from the gas stream and 1 was separated from the other products by gas chromatography. Alder-Rickert cleavage of the Diels-Alder adduct formed from cycloheptatriene and dimethyl acetylenedicarboxylate resulted only in the formation of a polymer and trace amounts of 1. A simple approach by Closs and Krantz based on the synthesis of 1-methylcyclopropene involved the addition of allyl chioride to a suspension of sodium amide in mineral oil at 80°C. Under the conditions employed, 1 could readily escape from the reaction mixture. Though a number of variations were tried, the yield of 1 never exceeded 10%. 

Its in situ formation in the presence of water, methanol, or dimethylamine provides the corresponding add, ester, or amide. Allyl 2>chlorotexafluoro> cyclopentenyl ether, prepared by the reaction of allyl alcohol with 1,2 dichlorohexafluorocyclopentene and sodium hydroxide, rearranges at 95 °C (Scheme 17). The Diels-Alder adduct of the product with hexachloro-cyclopentadiene is said to possess pestiddal activity. The adduct of allyl... 

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