Ring Chemistry

The C-ring of taxol has two functional groups available for manipulation a hydroxy group at C-7 and an acetyl group at C-4. The chemistry of the oxetane ring, which can be considered as a functional group at the C-5 position, is discussed in the following section. 

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As in the previous group, a potentially productive route into C7-ring chemistry is provided by the reduction of a metal halide with Na/Hg in thf in the presence of cycloheptatriene. WithMoCl5, [Mo(p -C7H7)(p -C7H9)] is produced and a variety of derivatives have already been obtained. 

This volume of Topics in Current Chemistry and another one, projected to appear within the next year are intended to cover most of the above-mentioned aspects of small ring chemistry, with emphasis being placed on the application in organic synthesis. State of the art reviews will be presented by individual authors who are themselves engaged in research on one or more of the subtopics. This exciting field has become so active that no single author would feel competent to write a comprehensive, up-to-date monograph. 

The synthesis of the benzene-ring substituted haloindoles entails more conventional aryl ring chemistry or de novo synthesis of the indole ring [1, 22-24], As expected, these haloindoles are far more stable than the C-2 and C-3 haloindoles. 

Respectfully dedicated to the Nestor of seven-membered-ring chemistry, Professor Tetsuo Nozoe. 

For ring systems that incorporate a pyridine ring, chemistry and reactivity of pyridone derivatives have been incorporated into Sections 10.06.5-10.06.9, wherever appropriate. For crystalline products, which represent most of the derivatives contained within this chapter, the compounds exist as the pyridone tautomer. 

P2. Pannala, A. S., Chan, T. S., O brien, P. J., and Rice-Evans, C. A., Flavonoid B-ring chemistry and antioxidant activity Fast reaction knetics. Biochem. Biophys. Res. Commun. 282, 1161-1168 (2001). 

The fundamental chemistry of donor-acceptor-substituted cyclopropanes is now well understood. This solid platform should allow many applications of known processes and exploration of new reaction types. A future challenge will be asymmetric syntheses which should be achievable, for instance, using Lewis acids containing enantiomerically pure ligands. Even more attractive might be cyclopropane formation under the influence of a suitable optically active catalyst. This intriguing approach could lead to enantioselective syntheses of many compounds in a most economical way. Finally it can be expected in the near future that transition metal induced reactions will also play an important role in this area of small ring chemistry. 

The following brief sections update some of the ring chemistry of borepins, but the reader is referred to Section 9.37.5 in CHEC-II(1996) for more detail, since much of the more recent work on these systems has been of a theoretical rather than an experimental nature. 

Some germanium-nitrogen ring chemistry has been developed. ... 

F. Antimony Rings That Have No Counterparts in Arsenic Ring Chemistry.. 571... 

The birth of small-ring chemistry was painstaking and difficult. It is sufficient to recall that the great chemists of the time, V. Meyer, A. von Baeyer, and E. Fischer, were persuaded that cycles with fewer than six carbon atoms in a ring were not capable of existence ... 

Bis(methylsulfanyl)-l,3-dithiole-2-thione (277) was prepared from 2-methylsulfanyl-acetonitrile (276) by classical heterocyclic ring chemistry (Scheme 53) <80CB1898>. 

The development of CN2S2-ring chemistry shows the value of seeking analogs of any system that does not appear to fit current rationalizations of structure, physical properties, or reactivities. It also illustrates the great value of new reagents (e.g., [SNS]+, NSC1, and N(SC1)2+). 

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