Synthesis of six-membered carbocycle

The intramolecular version of the described radical reaction provides an easy approach to the synthesis of six-membered carbocycles. ... 

The synthesis of six-membered carbocycles, which are subunits of a large variety of complex molecules, noticeably natural products, has long been pursued by organic chemists. Besides Diels-Alder cycloadditions, a large variety of other MBFTs to... 

Benzene and its Alkylated Derivatives.—Interest in direct synthesis of six-membered carbocyclic compounds, lacking over the years, has been stimulated by the current interest in cycloaddition reactions. A useful synthesis of 1,2,4-triphenylbenzene (1) by the Diels-Alder reaction of 2,3,5-tri-phenylcyclopentadienone (2) with dimethyl acetylenedicarboxylate has been reported (Scheme 1). 

Dipolar cycloaddUions. Interest in 1,3-dipolar cycloadditions increased dramatically during the past 20 years, largely because of the pioneering studies of Huisgen [7, 2] The versatility of this class of pericychc reactions in the synthesis of five-membered-ring heterocyclic compounds is comparable with that of the Diels-Alder reaction in the synthesis of six-membered-ring carbocyclic systems (equation 1)... 

SYNTHESIS OF BENZOTHIOPHENES BY FUSION OF SIX-MEMBERED CARBOCYCLIC RINGS TO THIOPHENES... 

Another example from the Spanish authors [14, 35] is especially interesting, as the cycloaddition leads to the formation of a compound with a seven-membered ring (Scheme 9). The literature shows that in recent years a tremendous amount of effort has been expended in trying to prepare carbocyclic five-membered rings by a route as simple and elegant as the Diels-Alder reaction for the synthesis of six-membered rings. [4c] Is a counterpart for... 

Since an annulated six-membered carbocycle is a common structural element of natural products, the Robinson annulation is an important reaction in organic synthesis. 

The tandem-Knoevenagel-ene reaction is a powerful tool to synthesize five-and six-membered carbocycles.2 5 The process is exemplified by the diastereoselective synthesis of 4a. Compound 4a has been obtained In both enantiomeric forms and as a racemate according to the procedure described here. The sequence includes the Knoevenagel reaction of citronellal, 1, and dimethyl malonate, 2, followed by the intramolecular ene cyclization of the chiral 1,7-diene 3 to yield the trans 1,2-disubstituted products 4a and 4b. Whereas the thermal cyclization of 3 at 160°C provides 4a and 4 b in a ratio of only 89.7 10.3, the Lewis acid... 

The Diels-Alder reaction is a useful way of synthesizing six-membered carbocyclic rings. Since ADC compounds are usually better dienophiles than the corresponding C=C compounds, the Diels-Alder reaction provides a good general route to pyridazines, and their reduced derivatives. Although vast numbers of examples of Diels-Alder reaction involving ADC compounds have been reported, not many of these have been aimed specifically at heterocyclic synthesis. 

In Delfourne and co-workers study toward the total synthesis of meridine, the Meldrum s acid derivative 91 was prepared. After several unsuccessful attempts to cyclize this material to the desired tricyclic compound 92, it was found that conversion into the quinone 93 was necessary for cyclization to occur (Scheme 4) <1997T1743>. Another approach to compounds with a central six-membered carbocyclic ring using Meldrum s acid derivatives has been... 

Preparation and characterization of l,l -diphosphaferrocenes with linear fused six-membered carbocycles <2007JOM55>. Synthesis and reactivity of trimethylsilyl-substituted phosphametallocenes <2007EJI553>. Synthesis and reactivity of tetramethylphospholyl complexes of scandium <2007JOM4595>. 

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