Fused saturated rings

Alkyl groups attached to the triazine ring are quite prone to halogena-tion [77CCC2182 84MI7 89H(29)2253 90H(31)1933], A 70% yield of 6-dichloromethyl-5-trichloromethyl-2-phenyl-l, 2,4-triazine was obtained when 5,6-dimethyl-2-phenyl-l,2,4-triazine was heated at 90°C with chlorine dissolved in an acetic acid-acetic anhydride-sodium acetate mixture [90H(31)1933]. Thionyl chloride similarly chlorinated 58 in the fused saturated ring [89H(29)2253] (Scheme 53). 

The example below shows how these 1,5-diketones may be quickly made by the Mannich (Chapter 27) and Michael (Chapter 29) reactions. Our pyridine has a phenyl substituent and a fused saturated ring. First we must disconnect to the 1,5-diketone. 

H. Other experiments prove that Me > OMe and Bu > H. Finally, the methylene group of a fused saturated ring >H, except in the case of the 3(5),4-trimethylenepyrazole (246). 

Other molecular structure factors, such as the presence of methyl or other aUcyl substitution also have an effect on DAD spectra. A single alkyl-group attachment shifts the absorbance spectrum of the parent compound upwards by 1-2 nm. Although additional alkyl substitution shifts the spectram even higher, the shift is not strictly additive. The presence of a fused saturated ring usually causes an upward shift of 5-10 nm. These smaU shifts in spectral location require that the DAD have corresponding resolution to see these changes. 

The designations cis and trans are also used to describe the stereochemistry of fused saturated rings at the bridgehead positions. Notice the difference between frans-decalin and m-decaUn with regards to the overall... 

Figure 2.23 For fused saturated rings, groups that are external to the rings at the bridgehead positions (atoms that are common to both rings) are designated c/s if they are both on the same face and trans if they are on opposite faces.

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