Imines five-membered cyclic

In a related way, c A-enals have been shown/or the first time to undergo NHC-catalysed reactions with a,/ -unsaturated imines to give five-membered cyclic derivatives (137) in an asymmetric manner, interestingly enough, cis- and trans-ensih have been found to exhibit distinct reactivity profiles under the so-established reaction conditions. 

Reduction of iV-(3-bromopropyl) imines gives a bromo-amine in situ, which cyclizes to the aziridine. Five-membered ring amines (pyrrolidines) can be prepared from alkenyl amines via treatment with N-chlorosuccinimide (NCS) and then BusSnH. " Internal addition of amine to allylic acetates, catalyzed by Pd(PPh3)4, leads to cyclic products via a Sn2 reaction. Acyclic amines can be prepared by a closely related reaction using palladium catalysts. Three-membered cyclic amines (aziridines)... 

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]. 

The CCl4-HF-SbF5 system developed by Jouannetaud and co-workers and used in the selective fluorination of imines (see Section 5.10.1) can be applied in the oxygenation of ketones and carboxamides as well. The hydroxylation of ketones is selective [Eq. (5.229)], provided that a five- or six-membered cyclic carboxonium ion preventing fluorination is involved.534,659 Fluorination, however, may be a side reaction with product distributions depending on quenching conditions (aqueous Na2CC>3 or HF-pyridine). Similar features are characteristic of the transformation of carboxamides.659... 

Catalytic reduction of the nitro group gives the amine 79 that cyclises instantly (chapter 7) to the imine 80 reduced in its turn to the cyclic amine 81. When the virtually planar five-membered ring of the imine settles on the surface of the Pd/charcoal catalyst it can choose between the side of the ring with a hydrogen atom or the side with the butyl group. It chooses the less hindered side and so the second hydrogen atom is cis to the first and the stereochemistry is correct (compare 81 with 71). 

Similar cyclic imines can be synthesized by intramolecular oxidative amination of aminoalkenes, which are less expensive than aminoalkynes. In the presence of catalytic amounts of [RuCl2(CO)3]2/l,3-bis(diphenylphosphino)propane and excess K2C03/allyl acetate, various aminoalkenes 19 possessing substituent(s) f3 to the amino group afforded five- and six-membered cyclic imines 20 in mod-erate-to-excellent yields (Eq. 8) [14]. 

The cyclocarbonylation of a,/ -unsaturated imines 54 also gave five-membered lactams 55 or 56 with or without 57 depending on the substitution patterns of the starting materials (Eq. 26) [40]. Such a useful [4+1] cycloaddition was applied to a cyclic imine 58 conjugated with a cyclohexenyl group to afford an interesting aza-tricycle 59 in 65% yield (Eq. 27). In the presence of an alkene such as ethylene, norbornene, and vinyltrimethylsilane, a similar cyclocarbonylation of a,/l-unsaturated imines 60 gave rise to a-alkylated /5,y-unsaturated lactam 61 in various yields (Eq. 28) [41,42]. Several plausible mechanisms are proposed for the formation of 61, but the elucidation of the entire mechanism calls for further work. 

A special situation arises when mercaptosuccinic acid is used as a mercapto component. Both the carboxyl functions are prone to nucleophilic attack by the imine nitrogen and give rise to five- (I) as well as six-membered (II) cyclic structures. Subsequently, Poop et al. showed by X-ray crystal structure analysis that a five-membered (III) cyclic structure is preferred over the six-membered (IV) cyclic structures (Scheme 8) [30]. 

The alkyne complex, (77s—C5H5X775—C5Me5)Ti(diphenylacetylene) reacted with C02 to give a five-membered metallacycle.53 Similarly, nickel complexes reacted with alkynes and C02 to yield the same type of metallacycles.54 The oxidative coupling of C02 with imines (Schiff bases) at electron-rich nickel(O) centers leads to cyclic carbamato complexes.55... 

Selected examples of intramolecular aminoalkyne hydroamination catalyzed by rare-earth metal complexes (see Figs.8, 16, and 18) are shown in Schemed and Tables. Formation of five-, six-, and seven-membered cyclic imines has been achieved in excellent yields. 

N-(l-Alkoxyalkyl)-aniides or -carbamates (2 X = OR), most frequently used as stable precursors for A -acyliminium ions, are usually prepared by one of the following routes (equations 7-13). For five- or six-membered cyclic cases a simple acid-catalyzed solvolysis of the hydroxy compound provides the alk-oxy derivative (equation 7). A silicon-assisted approach involves the TMSOTf-catalyzed reaction of bis(trimethylsilyl)formamide with aldehydes (equation 8). /V-(l-Trimethylsilyloxyalkyl)formamides are thus formed in good yields, which on TMSOTf-catalyzed solvolysis lead to the /V-( 1-alkoxyalkyl)form-amides. A third method is based on the NaBH4 reduction of imidates (equation 9), and has proved useful for a total synthesis of the insect poison pederine. Addition of reactive acid derivatives to imines constitutes another method (equations 10 and 11). Acylation with acid chlorides followed by treatment with ethanol in the presence of base leads to N-(l-alkoxyalkyl)amides. A one-step protocol using diethyl dicarbonate provides the corresponding carbamates. 2... 

However, it was observed [ 103] that reaction of titanium(IV) enolates derived from homophthahc anhydride and five-, six- and seven-membered cyclic imines also yield trara-adducts instead of the expected cu-isomers (Scheme 2.9). 

Aliphatic alkynylamines also undergo cyclization even without a protecting amino group (Scheme 23). Thus, 3-alkynylamines give l-pyrrolines in good yield via 5-endo-dig cyclization, whereas 5-alkynylamines undergo a 5-exo-dig cyclization to afford 2,3,4,5-tetrahydropyridines. In the case of 4-alkenylamines, both five- and six-membered cyclic imines are produced. 

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