Small-membered ring compounds

In some cases, the Grignard reaction can be performed intramolecularly. For example, treatment of 5-bromo-2-pentanone with magnesium and a small amount of mercuric chloride in THE produced 1-methyl-1-cyclobutanol in 60% yield. Other four- and five-membered ring compounds were also prepared by this procedure. Similar closing of five- and six-membered rings was achieved by treatment of a 6- or s-halocarbonyl compound, not with a metal, but with a dianion derived from nickel... 

Hydrogenation of fluorene Hydrogenation of fluorene provided, 34 wt % hexahydrofluorene, 6 wt % peihydrofluorene and 16 wt % cracked material as well as 44 wt % unreacted fluorene.The cracked material consisted largely of diphenyl with smaller proportions ortho methyl-substituted diphenyl. These products arise from cracking of the central five-membered ring. Compounds produced from hydrogenation of these compounds were also identified as well as small amounts of cycloalkanes. 

Conformational analysis of rings larger than cyclohexane is more complicated. These rings are also less common than cyclohexane, so we discuss their conformations only briefly. As can be seen from Table 6.1, the seven-membered ring compound cycloheptane has only a small amount of strain. Obviously, it is nonplanar to avoid angle strain. It does have some torsional strain, but the overall strain is comparable to that of cyclopentane. It is a fairly common ring system. 

In addition, a small amount of a six-membered ring compound is formed by the Diels-Alder reaction as a third product to give T, 4,4,5-tri-fluoro-1-cyclohexene. It is likely that both concerted and biradical mechanisms are involved [123]. 

The ylid anion (67) with chloroaminophosphines gave the phosphino ylids (68) and (69), and a small amount of the product (70) arising from -attack on (67). Both (68) and (69) with dichlorophosphines gave five-membered ring compounds, e.g. (71). The first air-stable a-diazophosphine (72) has been prepared and characterized by an X-ray crystal structure determination. ... 

Pyridone A doubly unsaturated six-membered ring compound with only one nitrogen and five carbons and one carbonyl group. Also known as pyrone. The hydroxyl tautomers are present only in small amounts. 

This paper summarizes the first investigations of three- and four-membered ring compounds by the technique of electron transmission spectroscopy (ETS). He will briefly discuss two general areas associated with the negative ion states of small ring hydrocarbons ... 

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