Similar Ring Compounds

FIGURE 16-5 Mechanism of the [Fe(trien)] -H202 Reaction. (Reproduced with permission from J. H. Wang, J. Am. Chem. Soc., 1955, 77, 4715. 1955 American Chemical Society.) 

FIGURE 16-6 Structures of Fe — S Protein-Active Sites, (a) Ferredoxin. (From E.-I. Ochiai, Bioinorganic Chemistry, Allyn and Bacon, Boston, 1977, p. 184.) (b) Clostridial ferredoxin. (Reproduced with permission from E. T. Adman, L. C. Sicker, and L. H. Jensen, J. Biol. Chem., 1973, 248, 3987.) (c) A model for the structure of the Fe Sg active unit. (Reproduced with permission from E.-I. Ochiai, Bioinorganic Chemistry, Allyn and Bacon, Boston, 1977, p. 192.) 

Methylcobalamin can methylate many compounds, including metals. The reactions of alkylcobalamins depend on cleavage of the alkyl — cobalt bond, which can result in Co(l) and an alkyl cation, Co(II) and an alkyl radical, or Co(III) and an alkyl anion, with the radical mechanism being the most common. The alkyl products can then react in a number of ways. Some of the reactions include the following  

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July, 1939 Structures of Some Similar Ring Compounds 1779... 

An enantioselective synthesis of (R)-(-)-2-amino-5-phosphonopentanoic acid is indicated in Scheme 46 and involves the alkylation of an A-protected 2-oxo-5-phenylmorpho-line derivative. The idea of stereochemical control in the alkylation of these and similar ring compounds seems to have stemmed from the asymmetric alkylation of the systems 342... 

The course of alkylation is also influenced by the steric arrangement of the enamine. 1-Pyrrolidino-l-cycloheptene gave approximately equal quantities of the C- and N-alkylated products in dioxane, while 1-pyrroli-dino-l-cyclooctene, and 1-pyrrolidino-l-cyclononene afforded N-alkylated products exclusively under similar eonditions (29). The reason for N alkylation in the eight- and nine-membered ring compounds is to be found in the conformation of these rings, which prevents full interaction of the unshared electrons on nitrogen with the n eleetrons of the double bond. 

In a similar base-catalyzed eyclization, Smrt et obtained a high yield of the pyrrolidone (21) from a y-halogeno-a-aminobutyro-hydroxamie acid and were unable to isolate any of the six-membered ring compound (22). 

Compounds containing a fused quinoline-tetrazole ring system (90 Z = N) behave similarly to compounds containing the simple tetrazole ring and give salts of type 91 (Z =... 

Conditions more accessible to rate measurements and, possibly, more favorable to a normal course of substitution (Section II, A) make the use of activated compounds such as nitro- and aza-sub-stituted derivatives desirable. In both cases, the activated halogeno-substituted five-membered ring heterocycle is also more reactive than a similarly activated six-membered ring compound. This... 

Woker points out that the closing of a chain compound to form a ring compound does not affect the odour much, thus the aliphatic terpineol of W. H. Perkin, Jr., 2 3 di-methyl 5 hexenol 2 has a verj similar odour to a-terpineol, their respective formulae being —... 

Alkenes, alkynes, and arenes (aromatic compounds) all contain carbon-carbon multiple bonds. Alkenes have a double bond, alkynes have a triple bond, and cneues have alternating double and single bonds in a six-membered ring of carbon atoms. Because of their structural similarities, these compounds also have chemical similarities. 

Shortly before this work by Pschorr, similar ring closures had been described for other compounds in which two benzene rings are already linked. Thus Graebe and Ullmann (1894) found that 2-diazobenzophenone can be converted into fluorenone in the analogous manner (Scheme 10-74). Similarly, when Staedel (1894) added nitrous acid to 2,2 -diaminobenzophenone he obtained some 1-hydroxyfluorenone. The ring closure of 2-benzylbenzenediazonium ion to give fluorene (Scheme 10-75) was described by Fischer and Schmidt (1894). 

Lim et al. also investigated HMTA-phenolic reactions with somewhat larger model compounds (e.g., two- and four-ring compounds) and established that similar reaction pathways to those described previously occurred.50 For these model compounds (as opposed to one-ring model compounds), which are more representative of typical oligomeric systems, increased molecular weight favored die formation of hydroxybenzylamines but not benzoxazines. This was suggested to be a steric effect. 

In some cases, the Grignard reaction can be performed intramolecularly. For example, treatment of 5-bromo-2-pentanone with magnesium and a small amount of mercuric chloride in THE produced 1-methyl-1-cyclobutanol in 60% yield. Other four- and five-membered ring compounds were also prepared by this procedure. Similar closing of five- and six-membered rings was achieved by treatment of a 6- or s-halocarbonyl compound, not with a metal, but with a dianion derived from nickel... 

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