Three of the six possible stereoisomers of dodecahydroacenaphthylene, f,t,t-ufolane (l), c,c,f-ufolane (3), and c,c,c-ufolane The names derived from the IUPAC nomenclature rules for the six possible stereoisomers 1 -6 are quite long. Therefore, we propose the following simple notation: For the dodecahydroacenaphthylenes with trans-linkage of all rings, viz. for 1, we have already proposed the name "ufolane"['ol. This name will now be used for all stereoisomers of dodecakydroacenapktkylene. For the notation of the configuration we follow the rules of Landa and Vanek?1. The molecules are drawn in such a way that the fivemembered ring is at the top.2. The hydrogen at the central tertiary carbon atom lies above the paper.3. The relation of the carbon -hydrogen bond at the central tert. carbon atom to the carbon-hydrogen bonds at the other tert. carbon atom is characterized as cis or trans, beginning with C-1 (unsystematic numbering) and continuing clockwise.4. In addition to the rules of Landa and Vanek@] we propose: If there are two possibilities following rule 3 the direction is: cis precedes trans, e.g. the correct name for 3 will be rac-cis,cis,trans-ufolane or -abbreviated -rac-c,c,tufolane and not rac-trans,cis,cis-ufolane (rac-t,c,c-ufolane) as drawn in 3a, if the racemate and not a specific enantiomer is to be indicated.c,c,c-Ufolane (5) seems to be the most valuable isomer with respect to its use as a propellant because of its high mass density.Vanek et aLc6] showed that five isomers are formed by catalytic hydrogenation of acenaphthene; the authors separated them by thermodiffusion and isolated one by preparative GC. The isomers were characterized by means of their G C retention indicesr5a6]. Furthermore, the assignment of the structure of the five isomers was attempted on the basis of their 13C-NMR spectral"] or of the G C retention indices on columns with graphitized thermal carbon black['*'. However, an unequivocal structural assignment was still lacking. We describe here the synthesis of the three stereoisomers 1, 3, and 5. Scheme IChem.

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