Heterocycles ring opening

J. Lehmann and co-workers, Abstracts to First International Symposium on Polymerisation of Heterocycles (Ring-Opening), Warsaw/ ablonna, Poland, June 23-25,1975, p. 141. 

Side transformations also take place after heterocyclic ring-opening. 

Type cycloadduct 24 (Scheme 1) was obtained as the major product on cycloaddition of n-chloranil with l-ethoxycarbonyl-l/7-azepine <1982H(19)1197>. Treatment of 4-ethoxycarbonyl-5-chloro-l,2,3-thiadiazole with ethylenediamine under basic conditions occurs with heterocyclic ring opening/recyclization to form bis(triazole)-fused thiadiazepine 77 (R = COOEt) (Scheme 14). The benzo-fused analog was prepared by the similar reaction with o-phenylenediamine <1999CC2273>. 

T. Saegusa, Y. Nagura, and S. Kabayashi, Macromolecules 6, 495 (1973) T. Saegusa, Int, Symp. Polymerization of Heterocycles (Ring-Opening), IUPAC, 1st, 1975, Abstr.,... 

It was impossible to introduce the second nitro group into 6-nitroanthranil because of the heterocycle ring opening, as shown in Scheme 2.12 however, 3-carbomethoxy-6-nitro-2,l-benzisoxazole is more easily nitrated to 4,6-dinitro derivative [130],... 

The 5-arylidene derivatives (e.g.,96) react with Grignard reagents via 1,4-conjugate addition to the exocyclic double bond to afford 97 [Eq. (28)] heterocyclic ring opening does not occur under these conditions.121 126,134,138 Other nucleophiles, such as p-thiocresol and piperidine, add 1,4 to exocyclic double bonds to give the simple adducts 97 (R = SAr and NR 2, respectively). 134 5-Methyl-3-phenyl-2-phenylimino-4-thiazolidinone undergoes... 

Related heterocyclic ring openings occur, although the yields of organolithiums are often low, owing to secondary reactions with ethers... 

The elegant work of H. C. van der Plas and colleagues provides proof that the Sn(ANRORC) mechanism (addition of the nucleophile to the heterocycle, ring opening, and ring closure) operates in some Chichibabin reactions under homogeneous conditions (85T237). 

Bridgehead N-heterocycles, ring-opening polymerization of 83CRV549. 

An enhanced heterocycle stress in the coordination sphere leads, in turn, to a sharp drop in the endocyclic bond strength. This causes heterocyclic ring opening to give bipolar ions with the coordination bonds remaining unchanged. 

S. Penczek, (ed.). Polymerization of Heterocycles (Ring Opening), Pergamon Press, Oxford,... 

The second mechanism is an Sn(ANRORC)—addition of nucleophile to the heterocycle, ring opening and ring closure. It was proposed by and heavily investigated and reviewed by H. C. Van der Plas and co-workers as a possible mechanism for some Chichibabin amination cases under homogenous conditions. The hypothesis comes from his extensive... 

The spiropyran example in which the photochromism develops following the transformation of a colorless isomer to a violet system is closely related to the structural isomerism observed in the target photochromic substance, a di-azabicyclo[3.1.0]hex-3-ene (VI) synthesized in Sequence F. In both instances, the photoisomerization involves heterocyclic ring opening with formation of zwitterion VII ... 

Yi W, ZhangJ, Huang S, Weng L, Zhou X. Reactivity of TpMe2-supported yttrium alkyl complexes toward aromatic N-heterocycles ring-opening or C=C bond formation directed by C-H activation. Chem Eur J. 2014 20 867-876. 

J. Kops, S. Hvilsted and G. Sorensen, Proceedings of 1st Int. Symposium on Polymerization of Heterocycles (Ring Opening) Jablonna 1975 P 132. 

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