Imines regioselectivity

Deprotonation of / /-cyclohexylfluoroacetone imines by lithium hexamethyl-disilazide or tertiary butyl lithium at very low temperature allows a regioselective alkylation at the carbon carrying fluorine [773] (equation 98). 

Skraup proposed a simple mechanism involving imine formation followed by an acid-mediated cyclization. Unfortunately the observed regioselectivity is not consistent with the proposed mechanism when, for example, electron-rich aniline 4 reacts with a, 3-unsaturated aldehyde 5 to give quinoline 6. ... 

Substituted TMMs also participate smoothly in imine cycloaddition to generate more structurally elaborate pyrrolidines. The regioselectivity of these reactions is similar to that of olefin addition, although subsequent isomerization of the initial adduct is often observed. For example, the cyano system produced the thermody-... 

The stoichiometric hydroamination of unsymmetrically disubstituted alkynes is highly regioselective, generating the azametaUacycle with the larger alkyne substituent a to the metal center [294, 295]. In others words, the enamine or imine formed results from an anti-Markovnikov addition. Unfortunately, this reaction could not be applied to less stericaUy hindered amines. 

Hydroamination of terminal alkynes with primary amines has been performed using organoactinides as catalysts [301, 302]. The organouranium complex Cp 2UMe catalyzes the regioselective formation of imines in fair to high yields (Eq. 4.82). 

However, with 1-hexyne or phenylacetylene, the thorium catalyst induces a dramatic inversion in regioselectivity giving imines with various amounts of dimerized alkyne (e.g., Eq. 4.84) [301],... 

Organolanthanides are efficient catalyst precursors for the regioselective (>95%) IH of primary aminoalkynes, forming five-, six-, and seven-membered cyclic imines via Exo-Dig processes (Eq. 4.86) [303, 304]. 

Ketone imine anions can also be alkylated. The prediction of the regioselectivity of lithioenamine formation is somewhat more complex than for the case of kinetic ketone enolate formation. One of the complicating factors is that there are two imine stereoisomers, each of which can give rise to two regioisomeric imine anions. The isomers in which the nitrogen substituent R is syn to the double bond are the more stable.114... 

Scheme 1.11 provides some examples of alkylation of imine and hydrazone anions. Entries 1 and 2 involve alkylation of anions derived from IV-alkylimines. In Entry 1, two successive alkyl groups are added. In Entry 2, complete regioselectivity... 

The reaction is also applicable to a wide structural variety of 1,3-dienes, as demonstrated by the reaction of 2-furfural-p-anisidine imine (Table 9). All dienes react with the aldimine regioselectively at the diene termini bearing the highest electron densities and provide bis-homoallyl amines with excellent 1,3-syn diastereoselectivity. No C4-adducts are formed in these reactions. 

Selective transformations Selective styrene ring opening [103] One-pot domino process for regioselective synthesis of a-carbonyl furans [104] Tandem process for synthesis of quinoxalines [105] Atmospheric oxidation of toluene [106] Cyclohexane oxidation [107] Synthesis of imines from alcohols [108] Synthesis of 2-aminodiphenylamine [109] 9H-Fluorene oxidation [110] Dehydrogenation of ethane in the presence of C02 [111] Decomposition of methane [112] Carbon monoxide oxidation [113]... 

The [4+2] cycloaddition of 2-amino-l-thia-3-azabutadienes, for example, 652, formed in situ from W-(trimethylsilyl)-imines and PhNCS, and PTAD leads to the regioselective formation of cycloadducts 653 with complete endo-stereoselectivity (Equation 96) <1995S985>. 

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