Medium-ring heterocycles

Scheme 5. Chiral medium-ring heterocycles that have been synthesized by catalytic RCM and resolved by the Zr-catalyzed kinetic resolution are subject to diastereoselective alkylations that afford synthetically useful materials in the optically pure form...

As the representative data in Table 6.4 indicate, the Zr-catalyzed resolution technology may be applied to medium-ring heterocycles as well in certain instances (e. g. entries 1 and 2), the starting material can be recovered with outstanding enantiomeric purity. Comparison of the data shown in entries 1 and 3 of Table 6.4 indicates that the presence of an aromatic substituent can have an adverse influence on the outcome of the catalytic resolution. The fact that the eight-membered ring substrate in Table 6.4 (entry 4) is resolved more efficiently may imply that the origin of this unfavorable effect is more due to the... 

Enantiomerically enriched medium-ring heterocycles are synthesized using the same protocol. Silicon or nitrogen containing heterocycle 92a or 92b " is synthesized using 75a [Eqs. (6.63) and (6.64)]. Eight-membered nitrogen heterocycles... 

Nitrogen heterocycles are attacked by cyanogen halides at the nitrogen. In the reaction of cyanogen bromide with the saturated, fused oxazole (182), a fused medium-ring heterocycle (183) is formed when the reaction is carried out under solvolytic conditions... 

The abundance in natural products of medium ring heterocycles, particularly eight-membered heterocycles with one nitrogen atom, ensures the chemists interest for such a popular target. Efforts to diversify the syntheses of azocines, hydrazocines, and azocanes are intrinsically linked to their potentially useful biological activities <2006W02006001463>. 

Medium ring heterocycles, sigmatropic rearrangements in synthesis of 80YGK381. 

Synthesis and biological perspectives of benzannulated medium ring heterocycles 07H(71)1011. 

Buchwald and co-workers developed a simple method for the preparation of medium ring heterocycles (7-, 8-, 9-, and 10-membered). The process employs a Cu-catalyzed coupling of a ) -lactam with an aryl bromide or iodide followed by intramolecular attack of a pendant amino group (Scheme 4.11). In some instanees, the intermediate -lactam was observable but can be converted to the aza-heteroeyele by catalysis. Acetic acid was found to be superior to transition metal eomplexes as a catalyst for this ring-expansion process. 

Pericycttc Reactions Although a wide variety of ring-expansion processes through pericyclic cyclizations have been described, only a few cycloaddition methods were depicted for the direct generation of medium-ring heterocycles. The most attractive approaches were the [4-1-3] cycloaddition, the 1,3-dipolar cycloaddition of nitrone, and the type-2 intramolecular N-acylnitroso Diels-Alder reaction. 

For some reviews on medium ring heterocycles, see [a] P.A. Evans, A.B. Holmes, Medium ring nitrogen heterocycles. Tetrahedron 47 (1991) 9131-9166. 

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