Bridged rings synthesis

Practicable syntheses of four-, five, and six-membered carbocyclic rings have been achieved by reaction of a,to-di-Grignard reagents with silver(i) salts. Conversion of l,3-bis(chloromethyl)cyclopentane into norbornane was effected in 82% yield, but was the only bridged-ring synthesis reported. Stereospecific cyclic ketone formation using iron(O) compounds has been reviewed. ... 

As mentioned earlier in the discussion of cyclizations leading to (3-lactones, the (3-lactones formed from halolactonization of 1,4-dihydrobenzoic acids readily rearrange to produce bridged ring y-lac-tones.19 In some cases, the substitution pattern favors formation of the y-lactone even under conditions of kinetic control (equation 23).20 Synthesis of a variety of y-lactones by iodolactonization of dihydroben-zoic acid derivatives has been reported recently by Hart (equation 24).91 Attempted iodolactonization of the acid in the case where R = H resulted primarily in an oxidative decarboxylation however, iodolactonization was effected using the amide derivative. 

This attractive cyclization procedure also allows for the synthesis of bridged ring systems in good to excellent yields720,772-777. For example, seychellene, a complex tricyclic... 

Nitriles and nitrilium salts, heterocyclic synthesis involving, 6, 95 Nitro-compounds, heteroaromatic, ring synthesis of, 25, 113 Nitrogen-bridged six-membered ring systems, 16, 87... 

Double cyclizations to butenolides and furanes. Radicals can undergo intramolecular addition to triple bonds when separated by three carbons. This strategy can be used for synthesis of butenolides (equation 1) and -substituted furanes (equation II). Cyclization of vinyl bromides." Fused and bridged ring systems can be prepared... 

Verbrugge, P. A., Tieleman, J. H., Van der Jagt, P. J., Bickelhaupt, F. Bridged ring compounds by malonic ester synthesis. Synth. 

There are many examples of intramolecular cyclizations of carboxylate enolates which lead to fused-and bridged-ring systems. The reaction shown in Scheme 71, which was used by Danishefsky et al. as a part of their synthesis of ( )-quadrone, is illustrative. ... 

In conclusion, the Wagner-Meerwein rearrangement can be a useful component of a synthetic strategy provided its stereoelectronic requirements can be met and the possible pathways are limited. It has been of particular value in the synthesis of bridged ring systems in which the strategy requires the modification of the skeletal framework. 

This new cyclization method was used as the key step in the synthesis of a substance containing the bridged-ring system of the gibberellin family of plant hormones.4 The tricyclic keto ketal (3) was used to supply final rings A, B, and C. 

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