Cross-coupling of imines

In addition, the cross-coupling of imines with allyl alcohols to generate Man-nich-type reaction products proceeded efficiently under similar conditions in methanol and ionic liquid ([ l- -butyl-3-methlyimidazolium] PFg) [19, 20] (Eq.9). 

Cross-coupling between allylic alcohol and aldehyde is efficiently catalyzed by RuCl2(PPh3)3 in water to form an aldol-type product 48 [22], This reaction has limitations in the substituents of the aldehydes, and the use of aliphatic aldehydes provides complicated mixtures. Cross-coupling of imines with allylic alcohols under similar conditions generates Mannich-type reaction products 50 as major products, together with aldol-type products 48 [22], The selectivity of the reaction was improved by using methanol as the solvent, whereupon no aldol-type product was observed (Eqs. 12.19 and 12.20). 

Scheme 27 Cross-coupling of imines and semi-stabilized phosphoniums...

Synthesis of 1,2-aminoalcohols via cross-coupling of imines with ketones or aldehydes can be achieved using TifOPr-r /c-CsHgMgCl in Et20, although some ketones form cm-2,3-dialkyl aziridines predominantly. ... 

It is known that electrochemical reduction of oximes in protic media occurs in two steps the N—O bond is first reduced to form an imine and the latter is then reduced to afford a primary amine1,29. Tallec has shown that the amine from oxime 33 can be trapped intramolecularly (equation 16)35. Interestingly, the SS diastereomer predominates the chiral pyrrolidine ring derivative serves to control the stereochemistry of formation of the new benzylic chiral center. Electrochemical reductive cross-coupling of O-methyl oximes with carbonyl compounds in isopropanol at a tin cathode affords adducts (equation 17) which can be reduced further to 2-amino alcohols36. In this fashion, menthone could... 

Imine formation. An example of this route is Echavarren and Stille s use of a simple intramolecular imine formation between a quinone moiety and an amino group to complete the nucleus (Scheme 25) of amphi-medine 105 (88JA4051). The quinone 159 was prepared by a palladium-catalyzed cross-coupling of 5,8-dimethoxyquinolin-4-yl triflate 157 (from... 

Enediynes. A route to funct --e cross-coupling of chloroenynes s Insertion of C=0 into silacyek .tanes to form cyclic silyl enol etht a-Vinyl-fi-lactams. Imines i crcerated in situ from triallyl phospi... 

In 2003, when the second edition appeared, it was clear that the Stille chemistr/ had really come of age, as shown by the increasing number of applications of palladium-catalyzed cross-coupling reactions of vinyl- and arylstannanes in natural product synthesis and in advanced organic synthesis. In the past decade, these types of applications, of course, remained very important and, in addition, the use of allylstannanes in palladium-catalyzed coupling reactions received much attention. Cross-coupling of allylstannanes with imines also forwarded the area of asymmetric catalysis. 

Liebeskind and Liu developed a copper-catalyzed synthesis of pyri-dines from a,(3-unsaturated ketoxime O-pentafluorobenzoates and alkenylboronic acids in 2008 [118], This cascade reaction consisted of a novel A/ -iminative, Cu-catalyzed cross-coupling of alkenylboronic acids at the NsO bond of a,(3-unsaturated ketoxime O-pentafluorobenzoates, electrocyclization of the resulting 3-azatriene, and air oxidation at the last stage. Highly substituted pyridines were formed in moderate to excellent isolated yields (Scheme 3.59). 

The dehydrogenative cross-coupling of primary alcohols in die presence of an amine has been further extended to the synthesis of a,p-unsaturated aldehydes via the formation of imine intermediates. 

TMSCl is essential as a promoter in a low-valent vanadium-catalysed reductive cyclotrimerization of aliphatic aldehydes, producing 1,3-dioxolanes (equation 4). It is also an essential component in the zinc-induced intramolecular imine cross coupling of diarylidene sulphamides subsequent cleavage provides a route to unsymmetiical l,2-diaryl-l,2-diaminoethanes (equation 5). It acts as an activating agent in the samarium-promoted cyclopropanation of allylic and a-allenic alcohols. 

Scheme 3.16 The asymmetric cross-coupling of a-aminoaikyl radical with imine anion radical [63]...

The cross-coupling of allenic alcohols with n-components (i.e., imines, alkenes, alkynes) has also been investigated by Micalizio to prepare substituted 1,3-dienes bearing ally lie amine functionality when reacted with imines (Scheme 23) [42]. The strategy is based on the reactivity of azatitanocyclopropanes 36 formed by... 

Generally, the alkynes can be prepared by the following two types of methods (3-elimination of CF3-containing hal-ogenated alkenes and a cross-coupling of trifluoromethy-lated acetylide with various halides in the presence of palladium catalyst, as shown in Scheme 26.49. Additionally, the reaction of the lithium acetylide with various electrophiles, such as carbonyl compounds, imines, and... 

A useful method for the preparation of functionalised thiazoles has been described. Palladium catalysed cross coupling reactions between 4-thiazolyl-5-acetyl triflates 36 and alkynes afforded 4-alkynyl-5-acetylthiazoles 37 in good yields (56-82%). If 37 is then treated with ammonia in methanol, thiazolo[5,4-c]pyridines 39 are formed, probably via the intermediate imine 38 which then undergos a regioselective 6-endo dig cyclisation <99EJOC3117>. 

Miller and co-workers have reported the use of thiazolylalanine-derived catalyst 65 to render the aldehyde-imine cross-coupling enantioselective [56]. The authors comment on the time sensitivity of this transformation and found that racemization occurs when the reaction goes to complete conversion. Electron-deficient aldehydes are the most efficient couphng partners for various tosylamides leading to the corresponding products 66, 68, and 69 (Scheme 8). 

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