Hydrogen autotransfer

G. Guillena, D. J. Ram6n, M. Yus, Chem. Rev. 2010, 110, 1611-1641. Hydrogen autotransfer in the iV-alkylahon of amines and related compounds using alcohols and amines as electrophiles. 

F. Alonso, F. Foubelo, J. C. Gonzalez-Gomez, R. Martmez, D. J. Ramon, P. Riente, M. Yus, Mol. Divers. 2010, 14, 411 24. Efficiency in chemistry from hydrogen autotransfer to multicomponent catalysis. 

Just taking a quick look at the different chapters, one can realize which areas of each field are mature and which can evolve immediately. Although it is very difficult to venture a general trend for the whole area, we could emphasize that there is not a tmly enantioselective version for the mono-activated hydrogen autotransfer reaction. The use of first-row transition metals is almost an unexplored Blue Ocean , in all aspects. Furthermore, the possible impact of green neoteric solvents, including deep eutectic mixtures, supercritical fluids, and bio-based solvents, on the hydrogen transfer process is definitely unknown. 

P-Alkylation of Alcohols Using Hydrogen Autotransfer Reactions... 

Scheme 3 General mechanism for alcohol-based borrowing hydrogen (a) or hydrogen autotransfer reactions (b)...

The direct nucleophilic substitution reactions (Scheme 2) [16-22], restricted mainly to n-activated alcohols such as secondary arylmethanols, allylic and propargylic alcohols, and tertiary alcohols that can readily form stable carbocationic intermediates, are mechanistically different to hydrogen autotransfer reactions. Although these reactions are not the focus of this chapter, since they are also very relevant research areas, this brief introduction is anticipated to provide potentially helpful references to assist interested researchers in their studies, especially in boardline research where elucidation of reaction mechanisms is difficult. 

In the case of A -alkylation reactions by hydrogen autotransfer processes, asymmetric reactions, nano materials, electrochemical methods, biomimetic methods, reactions using amines as the alkylating reagents, the more practical aerobic N-alkylation methods, and even some simple and efficient TM-free methods have also been reported in recent years. It was proposed that, in addition to anaerobic dehydrogenative for activation of the alcohols (Scheme 4, methods A-B), more alternative protocols should also be available, which may include the use of... 

Hydrogen Autotransfer A-Alkylation Reactions Using Alcohols as the Alkylating Reagents... 

Biomass-based alcohols could also be employed directly as substrates in N-alkylation reactions, making the hydrogen autotransfer method more practical. In 2011, Martin-Matute and co-workers reported a [Cp IrCl2]2-catalyzed method for synthesis of secondary aminosugars from primary aminosugars with simple alcohols and primary carbohydrate alcohols (Eq. 20) [106]. In 2009, Stephens, Marr and coworkers reported that a one-pot bio- and chemo-catalytic process could be used for direct conversion of crude glycerol from biodiesel production to valuable secondary amines in a biphasic system without intermediate separation of 1,3-propanediol... 

In 2014, by employing the hydrogen autotransfer method, Zhao and co-workers reported the first enantioselective amination of alcohols to chiral secondary arylamines in high yields and high ee up to 97 % (Eq. 56, Scheme 31) [178]. Intramolecular amination could also be achieved to give quinoline 24 with 68 % ee. The authors proposed that the high enantioselectivity might be attributed to the cooperation of the iridium complex 25 and the chiral phosphoric acid 26. 

Later in the same year, Uozumi, Yamada, and co-workers also reported an inwater dehydrative A(-alkylation reaction under air using a heterogeneous boron-iridium heterobimetallic Polymeric Catalyst 34 (Scheme 35) [184]. This method is suitable for the reactions of benzylic and aliphatic alcohols with ammonia, and primary, secondary, and cyclic amines. Different to usual hydrogen autotransfer reactions, which require basic conditions, the reactions of benzylic, aliphatic, and secondary amines and ammonia require a pH 4 aqueous buffer solution under microwave conditions. The catalyst can be recovered and reused at least twice without loss of activity. 

Sundararaju B, Tang Z, Bruneau C et al (2010) Ruthenium-catalyzed cascade N- and C(3)-di-alkylation of cyclic amines with alcohols involving hydrogen autotransfer processes. Adv Synth Catal 352(18) 3141-3146... 

Yang H, Mao R, Cheng Get al (2014) An efficient homogeneous gold(l) catalyst for A-alkylation of amines with alcohols by hydrogen autotransfer. Tetrahedron 70(46) 8829-8835... 

Martmez-Asencio A, Ramon DJ, Yus M (2010) A-Alkylation of poor nucleophilic amine and sulfonamide derivatives with alcohols by a hydrogen autotransfer process catalyzed by copper(ll) acetate. Tetrahedron Lett 51(2) 325-327... 

Cano R, Ramon DJ, Yus M (2011) Impregnated ruthenium on magnetite as a recyclable catalyst for the N-alkylation of amines, sulfonamides, sulfinamides, and nitroarenes using alcohols as electrophiles by a hydrogen autotransfer process. J Org Chem 76(14) 5547-5557... 

Mehta A, Thaker A, Nandan SR et al (2014) Reinvestigating Raney nickel mediated selective alkylation of amines with alcohols via hydrogen autotransfer methodology. Appl Catal A Gen 478 241-251... 

Choo GCY, Miyamura H, Kobayashi S (2015) Synergistic cascade catalysis by metal nanoparticles and Lewis acids in hydrogen autotransfer. Chem Sci 6(3) 1719-1727... 

Ramachandran R, et al. Ruthenium(II) carbonyl complexes designed with arsine and PNO/PNS ligands as catalysts for Af-alkylation of amines via hydrogen autotransfer process. J Organomet Chem 2015 791 130-40. 

Catalytic systems have been developed for the synthesis of primary, secondary, and tertiary amines from alcohols. Preparation of primary amines has been performed by hydrogen autotransfer mono-eoupling of ammonia to alcohols (Scheme 12.2). Milstein, Vogt, and Beller have all reported conditions for the mono-allq lation of ammonia with benzylie and aliphatic alcohols. Vogt s and Beller s protocols permit the use of seeondary aleohols, providing access to aZp/ra-branched primary amines. Beller s Ru/xantphos system is also suitable for the diamination of diols and the eonversion of hydrory esters to primary amino esters. 

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