P ring-opening

Dreyfuss, P., Dreyfuss, M.P., Ring Opening Polymerization. Frisch, K.C., Reegen, S.L., eds. (1969) Marcel Dekker, New York, Chapter 2... 

Formation of an enolate from a lithiated epoxide could occur by two mechanisms a-ring opening (vide supra) followed by insertion of the carbene in the LiOC-H bond or electrocyclic P-ring opening (Scheme 18). There is some experimental support for both pathways [69,70]. 

Figure 6. a ring opening and p ring opening of indan and... 

Scheme 5 Active chain-end mechanism in the cationic polymerization of glycidol (a) a- and (b) p-ring opening preserves the CH2OH substituent.

Epoxides provide another useful a -synthon. Nucleophilic ring opening with dianions of carboxylic acids (P.L. Creger, 1972) leads to y-hydroxy carboxylic acids or y-lactones. Addition of imidoester anions to epoxides yields y-hydroxyaldehyde derivatives after reduction (H.W. Adickes, 1969). 

The last group of reactions uses ring opening of carbonyl or 1-hydroxyalkyl substituted cyclopropanes, which operate as a -synthons. d -Synthons, e.g. hydroxide or halides, yield 1,4-disubstituted products (E. Wenkert, 1970 A). (1-Hydroxyalkyl)- and (1-haloalkyl)-cyclopropanes are rearranged to homoallylic halides, e.g. in Julia s method of terpene synthesis (M. Julia, 1961, 1974 S.F. Brady, I968 J.P. McCormick, 1975). 

The thermal ring opening of l,2-bis(trimethylsiIoxy) cyclobutenes (from acyloin condensation of 1,2-dicarboxylic esters) was used in ring expansion prodecures (see p. 53f.). 

Nucleophilic ring opening of epoxides by ammonia (Section 16 12) The strained ring of an epoxide is opened on nucleo philic attack by ammonia and amines to give 3 ammo alcohols Azide ion also re acts with epoxides the products are p azido alcohols... 

P-Fluoroethylamines are accessible by ring opening of a2iddines with hydrogen fluoride in pyridine or with hydrogen fluoride and SOCI2 at low... 

The reaction of 2-methyla2iridine with boron trichloride [10294-34-5] lea.ds to replacement of all three chlorides by ayiridine rings to form tri(methylethyleneimine) boron [17862-61-2] (152). The reaction of boron trifluoride [7637-07-2] with ethyleneimine at — 78°C proceeds via substitution and subsequent ring opening to yield A/-P-fluoroethyl-fl-difluorobora2ene (153). 

J. Lehmaim and co- Ring-Opening), Warsaw-Jablorma, Poland, June 23-25, 1975, p. 141. 

The Kixnig reaction (Fig. 5) has been used to determine the amount of nicotinic acid and niacinamide. In this procedure, quatemization of the pyridine nucleus by cyanogen bromide is followed by ring opening to generate the putative dialdehyde intermediate. Reaction of this compound with an appropriate base, such as p-rr ethyl am in oph en o1 sulfate (47) or sulfanilic acid (48), generates a dye. The concentration of this dye is deterrnined c olo rime trie ally. 

Mechanistic studies (6,26,27,67) have shown that the acyl enzyme species is the ring opened compound (13), which can tautomerize to the transientiy inhibited amino acrylate (14), and both of these species can react further to give irreversibly inactivated enzyme. Three inactivated forms of the enzyme have been detected. Two, according to labeling studies, retain the complete clavulanate skeleton and the other retains only the carbon chain of the P-lactam ring. Stmcture (15) has been suggested as one possible inactivated form. 

Heteratisine, C22H33O5N, crystallises in prisms, has m.p. 262-7° (dec.), [a]f7° + 40° (MeOH), forms a hydrochloride, m.p. 265-270° (dec.), contains one methoxyl and one methylimino group, two active hydrogens and a lactone ring, opened by alkali and re-formed on acidification. In a later paper the same authors describe the isolation of benzoylheteratisine, C29H3,03N, m.p. 213-4°, [a]jf° + 73° (EtOH), which yields a hydrochloride, m.p. 218-221° (dec.), and is hydrolysed to benzoic acid and heteratisine the latter they suggest may not exist naturally in the plant but may be produced from benzoylheteratisine during extraction. 

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