1.6- Dioxaspiro 4,4 nonanes

Succinic anhydride is dimerised to 1,6-dioxaspiro [4.4] nonane-2,7-dione by heating with sodium hydroxide. Modification of an existing procedure by adding further sodium hydroxide after the initial reaction led to a severe exothermic reaction after heating for some 30 h which fused the glass flask to the heating mantle, probably at a temperature approaching 550°C. The reason for this was not known [1], At elevated temperatures and under influence of alkali, succinic acid condenses decarboxylatively beyond the dimeric spiroacetal, sometimes explosively. Contamination of the anhydride with base is to be avoided [2],... 

Figure 22. Interconversion profiles due to inversion of configuration (enantiomerization) of 1-chloro-2,2-dimethylaziridine and 1,6-dioxaspiro[4.4]nonane determined by complexation gas chromatography on nickcl(II) bis[3-(heptafluorobutnnoyl)-(1 / )-camphorate] 148,203 boxed profile calculated chromatogram202.

Succinic anhydride is dimerised to 1,6-dioxaspiro [4.4] nonane-2,7-dione by heating with sodium hydroxide. Modification of an existing procedure by adding further... 

On close inspection of the chromatograms, an elevated baseline can be discerned between the terminal peaks of the spiroketals. This peak distortion is caused by interconversion of the stereoisomers during separation. On-column enantiomerization leads to the formation of a plateau between the terminal peaks (Trapp et al., 2001). Such a kinetic phenomenon of molecular interconversion was first observed for 1.6-dioxaspiro[4.4]nonane... 

Figure 11. Semi-preparative-scale stereoisomeric separation of 1.6-dioxaspiro[4.4]nonanes on Ni-CAR2 (experimental conditions cf. text) (Schurig, 1987).

Dioxaspiro[5.5]undecane, D-70462 2-Ethyl-1,6-dioxaspiro[4.4]nonane, E-70043 2-Hydroxycyclononanone, H-60112... 

Francke, W., V. Hermann, B. Gerken, J. A. A. Renwick, and J. P. Vit6 2-Ethyl-1,6-dioxaspiro [4.4] nonane, principal aggregation pheromone of Pityogenes chalco-graphus (L). Naturwissenschaften 64, 590—591 (1977). 

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