N cyclization

Part B of Scheme 4.5 gives some examples of cyclizations induced by selenium electrophiles. Entries 9 to 13 are various selenyletherifications. All exhibit anti stereochemistry. Entries 14 and 15 are selenyllactonizations. Entries 17 and 18 involve amido groups as the internal nucleophile. Entry 17 is an 5-exo cyclization in which the amido oxygen is the more reactive nucleophilic site, leading to an iminolactone. Geometric factors favor N-cyclization in the latter case. 

Ohtani, B., Iwai, K., Kominami, H., Matsuura, T., Kera, Y., and Nishimoto, S. (1995) Titanium(IV) oxide photocatalyst of ultra-high activity for selective N-cyclization of an amino acid in aqueous suspensions. Chemical Physics Letters, 242 (3), 315-319. 

Inspection of the optimized geometries of the transition states for cyclization suggested that steric hindrance is important in cases where N cyclizes toward F.87 This steric explanation of the rates and regiochemistry of cyclization was... 

DKPs, and 2,6-DKPs can be distinguished on the basis of intramolecular C-N cyclization, tandem reactions, and synthetic methods used. 2,3-DKPs have been used in medicinal chemistry and are found in natural products such as antibiotics (piperacillin), cefoperazone, and bicyclomycin. 2,5-DKPs are common namrally occurring peptide derivatives and are frequently generated as unwanted by-products in the synthesis of oligopeptides. " ... 

Table 28 N-Cyclization of Derivatives of Cyclic Allylic Alcohols...

Another aspect of regioselectivity with many nitrogen nucleophiles is the ambident nature of the nucleophile, which can lead to products of the same ring size through either N-cyclization or O-cyclization (see Scheme 12 for an example). As shown by entries 1 and 2 in Table 25, preferential N-cyclization to 3-lactams has been effected by use of sulfonyl or acyloxy substitution on nitrogen. However, these sub-... 

Table 33 N-Cyclization of N-Acylaminomethyl Ether Derivatives of Allylic Alcohols (Equation 120)...

N-Tosyl carbamates, such as 325, derived from allylic alcohols, undergo the Pd(II)-catalysed cyclization to furnish oxazolidinones 326 under 1 atm of CO439. Analogous Pd(II)-catalysed N-cyclization of allenic N-tosylcarbamates has generated the corresponding vinylpalladium intermediate that could be further alkylated440. 

A kinetic study on the cleavage of A-methylphthalamic acid (31) in mixed acidic aqueous MeCN solvent revealed the formation of both phthalic anhydride (32) (through O-cyclization) and, V-meihylphlhalimide (33) (through N-cyclization). The formation of (33) decreased from 20% to 3% with increase in the content of MeCN from 2 to 70% (v/v).34... 

Cyclic secondary amines lead to N-cyclized tertiary enamines which are of great synthetic use. The rates of hydrolysis and the pKa values for the dissociation of N-protonated enamines decrease in the case of N-cyclic 1-TV-isobutenes in the sequence from pyrrolidino (22b) to piperidino (22c) to the morpholino (22d) derivative73, i.e. the pyrrolidino enamines hydrolyse fastest. However, enamines of 3,3-dimethylazetidine74 analogous to 22e and acyclic tertiary enamines react even faster8. 

Base-induced annulation has also been utilized in a synthesis of, for instance, the fluoroindole 104, which results from a 5-i 6i-/n -cyclization of the precursor 105 (Equation 27). Some related cyclizations could also be used in preparation of fluorinated 2-pyrrolines <2002S1917>. 

In the case of 6-trimethylsilyl-6-hepten-2-one, the 6-c /n-cyclization product was obtained exclusively, probably due to steric inhibition of 5-cxn-cyclization and electronic effects favoring radical formation in the 6-cwr/o-cyclization [Eq. (43)] [180]. 

Cationic n cyclizations can achieve remarkably stereocontrolled syntheses of benzo[a]quinol-izidines. For example, treatment of compound (243) with polyphosphoric acid leads to (244) and (245) ((244) (245) > 95 5) (Equation (23)) <83JOC5062>. 

Kolchina, E.F. Gerasimova, T.N. Cyclization of polyfluorinated 2-amino- and 2-acetamidodiaryl ethers into phenoxazine derivatives. Izv. Akad. Nauk SSSR 1990, 4, 846-849. 

The intramolecular amine-halogen copper-promoted indohzation was applied to the synthesis of more-complex indoles (Scheme , equations 1 ) [58-61]. Other examples in this category of copper-catalyzed amination are syntheses of the carbazole alkaloids murrayaquinone-A and ( )-bis-murrayaquinone-A [62], 3-aryl p-carbolin-l-ones [63, 64], carbazoles from donble C-N cyclization [65], pyrrolo[2,3-c]... 

Dieckmann reaction n, Cyclization by way of a base catalyzed intramolecular casein type reaction of esters with active delta or epsilon ethylenes See image). 

Polycyclization n. Cyclization in which more than one internal ring formation occurs. 

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