Ring Retention

Ring Retention. Whereas the photochemistry of a,/S-epoxy-ketones has been investigated in depth, the behaviour of, y-epoxy-ketones has previously been neglected. Photolysis of the steroidal /S,y-epoxy-ketone (470) results in 

Kirrman and R. Nouri-Bimorghi, Bull. Soc. chim. France, 1972, 2328. 

Miscellaneous. The cyclization of synthetic polyene epoxides provides a useful biogenetic-type chemical route to tetra- and penta-cyclic natural products. Thus the epoxide (478) has been used in the total synthesis of isoeuphenol, 24,25-dihydro-A -protosterol, and 24,25-dihydroparkeol,  

Morisaki, H. Ohtaka, M. Okubayashi, N. Ikekawa, Y. Horie, and S. Nakasone, 

Thermolysis of the epoxytosylhydrazones (495) provides a new synthetic route from a,i5-epoxy-ketones to cycloalk-4-yn-l-ones (496). i 2 

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In Rhodamine 6G, also sold as Rhodamine F5G [989-38-8] (15), the caiboxy estei gioup prevents fiee rotation of the lower phenyl group. Its position is roughly perpendicular to the plane of the other three rings. Retention of color strength is good because there is less electronic interaction between the lower ring and the rest of the molecule. 

FIGURE 7.16 Trapping of the phosphate of 5 -dGMP by the pyrido [1,2-a] indole quinone methide. The 13C-NMR shows most trapping with ring retention, labeled pyrido, with trace amounts of ring expansion, labeled azepino. ... 

The phosphorylation of alcohols by CEP-imidazole (41 X=N) with CEP-ring retention is already well-established. Following from the observation that CEP-pyrrole (41 X=CH) phosphorylates alcohols with CEP-ring opening, an explanation has been advanced based upon the differences in apicophilicities of the pyrrole and imidazole moieties in pentaco-ordinate intermediates (Scheme 10). A scale of relative reactivities based upon the reactions in the equations... 

The calculation of the loop b discussed m simplifted form in Section 4.5. Jt b based on the adoption of an approach to equilibrium of ethylbenzene with 60 per cent weight on the average, and a Cg aromatic ring retention ratio of 97 per cent weight... 

The reactions of cyclopropenes with metal complexes proceed either with ring retention or with cleavage of the C(1 C(3) cr bond. 

All the exchange reactions proceed with ring retention. This is not the case when the reactions are performed with monochlorophosphines instead of dichlorophosphines. A concomitant ring opening reaction with the exchange... 

Transformations to Other Heterocycles with Ring Retention... 

The results on the hydrolysis of the methyl ester are confirmed in Macomber s study on a wider range of esters [40] (R = methyl, neopentyl, and phenyl). Exocyclic cleavage occurs at considerably enhanced rates (/ = 6-8 h, whereas no reaction is observed for hydrolysis of acyclic analogues), leading to product with ring retention (Scheme 12). 

Copolymer Structure and Sequence Distribution. The free radical polymerization of cyclic ketene acetals had two possibilities forming two different structures. One was the ring opening producing a polyester, and the other was ring retention producing polyacetals. The free radicd polymerizations of monomer MDO... 

LithiumJliq. ammonia-sodium hydride Partial hydrogenation of isocycles with phenol ring retention... 

Cyclobutene (C2H5)2AlCl/ V(acetyl acetonate)3 Horn. -50 Ring retention (form 11)... 

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