Cyclization reaction scheme

The general method for preparation of heterocyclic enamino ketones, amide vinylogs, consists of a cyclization reaction (Scheme 6). The most convenient technique involves heating the starting substance in acetonitrile in the presence of silver perchlorate 137-139). 

High diastereoselectivity occurs in the addition of lithiated methoxyallene to chiral cyclic nitrones. The hydroxylamines obtained can be easily transformed into derivatives of 1,2-oxazine hydroxylamine, which are products of a novel [3 + 3] cyclization reaction (Scheme 2.182) (646, 647). 

Some heterocyclic nucleophiles may also be successfully employed in these cyclization reactions (Schemes 25 and 26) [131]. In contrast, no cyclization was observed in an aniline-based system (Scheme 27), which reflects the reduced nucleophilicity of the aniline nitrogen [142],... 

In addition to these studies, Swenton and coworkers have recently explored the effects of alkoxy substituents on the reactions [46]. The presence of a single methoxy group clearly enhanced the cyclization reaction (Scheme 32). For example, consider the oxidation of substrate 29a. The presence of a methoxy group para to the vinyl substituent raised the yield of cyclized product from 16% (25a above) to 47%. The methoxy group para to the vinyl substituent also proved to be compatible with the oxidative cyclization reaction having a methyl... 

Finally, zinc-copper exchange by treatment of FG-RZnI with Me2Cu(CN)Li2 provides copper species that add smoothly to various alkynes and which can also be used to perform cyclization reactions (Scheme 2.48) [98]. 

Transmetalations of alkenylstannanes with copper salts are reversible if they are performed with CuCl in polar solvents [101]. This has found application in cyclization reactions (Scheme 2.49) [102]. 

Azadiene 132, containing electron-donor and -acceptor substituents, has been shown by Gomper and Heinemann [81 AG(E)296] to be a suitable precursor of several five-membered rings by acid-catalyzed cyclization reactions (Scheme 33). Thus, oxazole 133 (86%), thiazole 134 (85%), and imidazoles 135 (22-38%) were obtained upon reaction of 132 with aqueous HC1, HC1/H2S, and RNH2 HC1, respectively. 

Reaction of R NCS with H2NCR2R3OCH gives benzamidothia-zolidines 63, which rearrange to thiazines 64, possibly through the reversibility of the cyclization reaction (Scheme 39) (80MI1). Thiazine-... 

Glycoside-fused dioxathiepins were synthesized by photochemical [1+6] cyclization reaction (Scheme 29). 

For the synthesis of 2-alkylthio-TA 36, several methods based on the cyclization of dithiourethanes (33, 34, and 35) are suggested (66TL3225 70AJC51 82CCC3268). Compounds 34 are intermediates, but dithiourethanes 33 and 35 were first isolated, then introduced into the cyclization reaction (Scheme 7). 

The SRN1 mechanism represents an excellent alternative to accomplishing the following intramolecular cyclization reaction (Scheme 10.42), which constitutes one of the steps in the synthesis of rugulovasines A and B (20, a-H and P-H), novel structures within the family of ergot alkaloids [58]. 

The radical addition of selenomalonate 149 or the corresponding malononitriles are excellent substrates for phenylseleno group transfer reactions to alkenes and alkynes.263 Malononitrile 150 can be used for annulation and cyclization reactions (Scheme 40) 264,265... 

The intramolecular carbenoid-carbonyl cyclization reaction (Scheme 2) is a particularly effective method for generating carbonyl ylide dipoles undoubtedly as a consequence of... 

The hydroxy aldehyde 108 was converted into lactone 109 (a 1 1 diastereomeric mixture) by a samarium-mediated cyclization reaction (Scheme 23) <1997TL8245>. 

In an example of a C-C bond formation in the construction of a 1,4-diazocine ring, racemic [2,5]benzodiazocines 67 were synthesized from hydroxylactams 66 via an iV-acyliminium ion-pyrrole cyclization reaction (Scheme 9) <2000H(52)273>. 

The procedure has been applied with success to conjugated systems such as bromoenyne 22 leading to substrates like 23 susceptible to undergoing cyclization reactions (Scheme 9-24 see Section 9.6.4) [53]. 

Our second method involves the utilization of a cyclization reaction [Scheme 5-2(b)]. We examined reactions that generate the negative charge of an acyllithium on the termini of Ti-conjugation chains [32]. 

Formation of imidazo[4,5-e]-1,2,4-triazines 119 has been observed to occur when 6-ethylamino-5-methylamino-1,2,4-triazines 118 react with benzamidine. However, in this case only the methylamino group at C-5 is substituted by the amidine, while the ethylamino group at C-6 participates itself as a nucleophile in an intramolecular cyclization reaction (Scheme 68) (78CPB3154). 

Table 1. Yields of 1,2-oxatellurol-l-ium chlorides 3 and telluroflavones 5 as obtained by the cyclization reaction (Scheme 3) of / -aryltelluropropenoyl chlorides 1...

Uozumi developed polymer-supported 2,2 -bis(oxazolin-2-yl)-l,l -binaphthyls 252 as chiral ligands for the asymmetric Wacker-type cyclization reaction (Scheme 3.81) [152]. In the presence ofthe polymeric catalyst derived from [Pd(MeCN)4](BF4)2] and 252 o-allylphenol, 253 was asymmetrically cychzed to give 254 in 46% yield with 95% ee. 

Diethyl 3-furylphosphonates are prepared in fair to good yields (55-90%) by a two-step procedure based on ceric ammonium nitrate (CAN)-promoted oxidative addition of diethyl 2-oxoalkyl- or 2-oxo-2-phenylphosphonates to vinylic acetates followed by an acid-induced Pall-Knorr cyclization reaction (Scheme 3.120). ... 

The use of Cp rings with pendant phosphines in CpCoL2 compiexes has aiso been reviewed.Carbonyl complexes of this type (Cp Co(CO)2) lose CO at room temperature to afford pendant phosphane adducts (equation 46). The cheiated phosphane can then be uncoordinated with ligands such as cod substitution of cod (Section 5.1.4) with alkynes allows the cobalt complex to participate in cyclization reactions (Scheme 26). 

Soon after, the Seidel group realized the first highly enantioselective [l,5]-hydride transfer/cyclization reaction (Scheme 4.5). In this work. 

In 2007, Chen and Zhu [21] detailed the total synthesis of the natural product using an acid-mediated domino P-ehmination/cyclization reaction (Scheme 14.7). 

The formation of cyclobutanones has been reported by Nawar and Le Tellier (1972 Le Tellier and Nawar, 1972a) and Dubravcic (1968). The cyclization reaction (Scheme 7.1) produces characteristic cyclobutanones derived from the fatty acids of the lipid. In recent years, as well as the well-known 2-dodecylcyclobutanone, 2-tetradecylcyclobutanone, 2-tetrade-cenylcyclobutanone and 2-tetradecadienylcyclobutanone have been found and synthesized in irradiated lipids, so the cyclization products of all main fatty acids has been observed. All the products are widely used to identify irradiated foodstuffs and to estimate the applied dose. 

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