Y ring

Monocyclic Carotenoids. Eighteen carotenoid hydrocarbons have been isolated from the ladybird beetle Coccinella septempunctata. Amongst the minor components were detected small amounts of the new y-ring derivatives 3, 4 -didehydro-y.i/f-carotene (6), 7, 8 -dihydro-y,i/f-carotene (7), and 7, 8, 1T,12 -tetrahydro-y,i -carotene (8). 

Barak, Y., Ring, A., Levy, D., Granek, L, Szor, H., and Elizur, A. (1995) Disabling compulsions in eleven mentally retatded adults an open trial of clomipramine SR./ Clin Psychiatry 56 459-461. 

Figure 2.5. Nucleophile selectivities determined from product analysis for the reactions of ring-suhstituted 1-phenylethyl derivatives (X-l-Y) with azide ion, acetate ion and methanol in 50 50 (v/v) water/trifluoroethanol. The selectivities are plotted against the appropriate Hammett substituent constant or a. Leaving group Y ( ) ring-suhstituted benzoates ( ) chloride (T) dimethyl sulfide (A) tosylate.

Path B Attack at a- or "y-ring carbon, with subsequent reaction not involving ring opening (discussed in this section). 

The pyrazine mono-iV-oxides show close similarity in their reactions to the pyridine AT-oxides.402-404 In the latter compounds the electronreleasing ability of the iV-oxide function is demonstrated by the activation of the a- and y-ring carbon atoms to electrophilic attack. Pyrazine mono-AT-oxides are predictably less activated to electrophilic substitution, and thus there have been no reports of the successful nitration of pyrazine /V-oxides. The pyrazine ring is, however, activated by the A-oxide function to nucleophilic attack, especially if the positive charge of the N atom is enhanced by formation of an intermediate with an electron acceptor. Thus, phosphoryl chloride treatment of pyrazine 1-oxide yields chloropyrazine391 and similar... 

All these cyclizations can be rationalized by the intermediacy of an imine (6) bearing a good leaving group (Y). Ring closure yields an unstable quaternary benzimidazole (7), which by loss of one of the nitrogen substituents (R3) attains aromaticity to give a 1,2-disub-stituted benzimidazole (8). 

Hi) Two-component syntheses, in which the five-membered ring can be built up either by a [2 + 3] process or by a [4 +1] process. The most usual variations of the [2 + 3] method are C2 + X3, C2 + X2Y and CX + CX2, while the [4 + 1] approach accommodates combinations such as C2X2 + X, C2X2 + Y and C2XY + Y. Ring closure reactions proceeding with C—C bond linkage are unknown in these heterocyclic systems. 

O Keeffe, M., and G. V. Gibbs (1985). Ah initio MO calculations on cyclodisilox-anes and other Si-Y-Si-Y rings and the problem of silica-w. J. Phys. Chem. 89, 4574-77. 

Nicolaou, K. C., King, N. P., He, Y. Ring-closing metathesis in the synthesis of epothilones and polyether natural products. Top. 

Fishbein et al. (1969) reported that, following intravenous administration of PBO to rats, there were 13 metabolites in the bile and 11 in the urine when the compound was labelled in the methylene diox y ring, and 24 metabolites in the bile and 26 in urine when the compound was labelled in the p-earbon position. These workers did not identify any of the metabolism products. 

Pipetting method (peristaltic pumps, y ringe driven, non-contact piezo, etc.)... 

A carotenoid unfortunately named neothxanthin, from the fish Neothunnus albacora, is considered to be e,e-caroten-3-ol (6) but has not been characterized fully.Further details of the absorption and mass spectra of the series of y-ring carotenoids obtained from the ladybird beetle Coccinella septempunctata have been published. It is unfortunate that the small amounts of material available did not permit determination of the chirality at C-6 of the y-ring (13). 

For amide enolates, the situation is similar in that, when R3 and Y are large, the transition structures of paths a and c are favored [158]. However, recall that acyclic amides invariably form Z(0j-enolates, so amide COj-enolates are only possible when R2 and Y are joined i.e., in a lactam. In contrast to ketone and ester enolates, however, the transition structures of paths b and d appear to be intrinsically favored when Y and R3 are small. This latter trend is (at least partly) contrary to what would be expected based on the simple analysis of Figure 5.9, but can be rationalized as follows. For the lactams, the R2 and Y substituents present a rather flat profile, so that interaction with R3 in path d is minimal. Additionally, the R2-Y ring eclipses the P-hydrogen of the enone in c, destabilizing this structure. For amide Z(0)-enolates and acceptors with an R3 substituent such as a phenyl, there may actually be an attractive interaction between Y and R3, favoring path b. 

There is an extensive and complex structural chemistry of boron-oxygen anionic species (polyborates), in aqueous or nonaqueous solution and in the melt or solid state, Six-membered ring formation dominates, but the structural chemistry of the species is complicated since boron exists in either 3- or 4-coordinate environments, or various combinations of these. Thus most polymeric species consist of (6—0)3 rings joined by boron atoms linked to an intervening oxygen atom, or y rings sharing a common boron atom. 

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