Ritter reaction, modified

In this modified Ritter reaction inversion at C-3 takes place, implying that the five-membered rings 40 have a czs-relationship between the alkyl substituent... 

In its utilization of acetonitrile, the oxazoline synthesis shown in Scheme 56 resembles a Ritter reaction.The procedure is convenient, but yields are variable the pyrolysis gives starting alkene plus acetamide as by-products. Another oxazoline synthesis and subsequent conversion to a cif-amino alcohol is discussed later (Scheme 85). A recent y-hydroxy-a-amino acid synthesis incorporates the following type of transformation (Scheme 57).If a three-day equilibration with anhydrous HBr was introduced iMtween stages i and ii, almost pure trans product was obtained. The paper has many usefol references. Yet another modified Ritter reaction is shown in Scheme 58. ... 

If the reactions are carried out in a nitrile as solvent, rather than dichloromethane, using triflic acid as catalyst, a modified Ritter reaction takes place, and the intermediate nitrilium ion traps the liberated amine, forming an amidine (Scheme 67). In an earlier reaction cf. Scheme 67) the lithium perchlorate catalyzed reaction of sulfenyl chlorides with alkenes in the presence of nitriles had also given l-amido-2-sulfenyl adducts. Ritter products are also obtained in good yields by anodic oxidation (Pt or C, 1.2-1.4 V) of disulfides in acetonitrile, in the presence of excess alkene, using B114NBF4 as supporting electrolyte (Scheme 68). ... 

Aziridines can be opened by thiols to give 2-amino sulfides. The expected complete Walden inversion in this reaction has been confirmed recently, in die case of cis- and rrans-stilbeneimine, whether the requisite prior activation of the aziridine is achieved by IV-protonation or sulfonation or benzoyl-ation. Hexavalent sulfur can be introduced by yet another modified Ritter reaction (Scheme 70). ... 

Functionality adjacent to the epoxide can modify its reactivity. For example, 2,3-epoxy sulfides can be converted to a thiiranium species upon treatment with TMS triflate. This intermediate reacts with 0-silyl amides regiospeci-fically to form l-substituted-3-hydroxy-2-thioethers. Simple primary amines undergo polyalkylation, but imines can be used as an indirect amine equivalent <1996T3609>. Nitriles react with functionalized oxiranes in a regioselective manner in a tandem epoxide opening-Ritter reaction (Equation 17) <2005JOC7447>. 

A modified Ritter reaction was used by Y.L. Janin et al. for the preparation of electron rich 1-aryl-3-carboxylisoquinolines, which are considered to be the eiectron-rich anaiogues of PK 11195, a faicipain-2 inhibitor. interestingiy, the standard Ritter reaction conditions (strong acid) ied to extensive decomposition of both starting materiais, but the use of HBF4 in ether gave rise to the desired dihydroisoquinoiine, aibeit in poor yieid. 

Reddy, K. L. An efficient method for the conversion of aromatic and aliphatic nitriles to the corresponding N-tert-butyl amides. A modified Ritter reaction. Tetrahedron Lett. 2003, 44, 1453-1455. 

Janin, Y. L., Decaudin, D., Monneret, C., Poupon, M.-E. Synthesis of methylenedioxy-bearing 1-aryl-3-carboxylisoquinolines using a modified Ritter reaction procedure. Tetrahedron 2004, 60, 5481-5485. 

A new and convenient method was found for the one-pot synthesis of symmetrical and unsymmetrical linear imides in the presence of SSA. The amidation of alcohols with nitriles in the presence of an acidic catalyst is known as the Ritter reaction. Salehi et al. have modified this method and developed the one-pot synthesis of a wide variety of linear imides instead of alcohols [97] (Scheme 5.17). 

H. G. Chen, O. P. Goel, S. Kesten, J. Knobelsdorg, Tetrahedron Letters 1996,37. 8129 A modified Ritter Reaction ... 

Carbonium hexachloroantimonates Modified Ritter reaction Acylamines... 

Modified Ritter reaction under mild conditions... 

The chiral Mn-salen catalysts have successfully been used in pharmaceutical industry processes. For example, enantioselective epoxidation of indene 43 under Jacobsen et al. s conditions provided epoxide 44 in 71% yield and 84—86% ee. It was reported that both yield and enantiose-lectivity were increased by adding 4-phenylpyridine N-oxide (PPNO) as co-oxidant in the system. A modified Ritter reaction converted indene oxide 44 into the c -amino alcohol 46. The enantiomeric purity of 46 was enhanced to >99% ee by formation of the corresponding L-tartrate salt followed by recrystallization. Amino alcohol 46 was identified as a critical component of the highly effective HIV protease inhibitor Indinavir 47 developed by Merck (White-house Station, NJ) (Scheme 35.12). ... 

H—1,3—Benzothiazines (e.g. 375) have been prepared by a modified Ritter reaction and characterised by methiodide formation (Scheme 84). 4H-1,4-Benzothiazines(377) are... 

The hydride abstraction reaction of NO+ has been employed in a modified Ritter-type reaction51 1 (Scheme 5.50, routea) as well as in ionic fluorination512 of bridgehead hydrocarbons (Scheme 5.50, route b). 

Olah et al. reported the triflic acid-catalyzed isobutene-iso-butylene alkylation, modified with trifluoroacetic acid (TFA) or water. They found that the best alkylation conditions were at an acid strength of about//q = —10.7, giving a calculated research octane number (RON) of 89.1 (TfOH/TFA) and91.3 (TfOH/HaO). Triflic acid-modified zeohtes can be used for the gas phase synthesis of methyl tert-butyl ether (MTBE), and the mechanism of activity enhancement by triflic acid modification appears to be related to the formation of extra-lattice Al rather than the direct presence of triflic acid. A thermally stable solid catalyst prepared from amorphous silica gel and triflic acid has also been reported. The obtained material was found to be an active catalyst in the alkylation of isobutylene with n-butenes to yield high-octane gasoline components. A similar study has been carried out with triflic acid-functionalized mesoporous Zr-TMS catalysts. Triflic acid-catalyzed carbonylation, direct coupling reactions, and formylation of toluene have also been reported. Tritlic acid also promotes transalkylation and adaman-tylation of arenes in ionic liquids. Triflic acid-mediated reactions of methylenecyclopropanes with nitriles have also been investigated to provide [3 + 2] cycloaddition products as well as Ritter products. Tritlic acid also catalyzes cyclization of unsaturated alcohols to cyclic ethers. ... 

The ability of thiol-ene click chemistry to retain high efficiency under the most benign reaction conditions was exempHfied by Ritter and Bardts, in the preparation of hydrogels based on methacryhc acid [224]. In this study, poly(methacrylic acid) polymers were modified with cysteamine and aUyl amine to afford complementary thiol-ene reactive polymer chains. Solutions of the polymer pairs in water were mixed in the presence of a radical initiator, and the formation of a highly elastic gel was observed within only 2 h at room temperature. The authors noted that this approach might have broad application for a rapid and straightforward access to hydrogel materials for which the properties could easily be tailored by the choice of the amine modifiers. 

The general structures of new surface active initiators are given in Table 1 (A1 and A2). With both Inisurfs it is possible to carry out emulsion polymerizations without additional stabilizers up to more than 50% solid contents. In particular, structure A2 fulfills all of the demands with respect to chemical stability against hydrolysis and ease of preparation (one-step synthesis via a modified Ritter reaetion). Strueture A1 has still ester bonds, but a sulfonate instead of a sulfate hydrophilie group. The synthesis occurs via a two-step procedure where by the first step is the preparation of the corresponding bis(phenyl alkyl)-2,2 -azobisisobutyrates (Pinner reaction) and the second step is the sulfonation of the phenyl ring. 

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