Rotane

The Simmons-Smith reaction is well suited for the synthesis of spirocyclic compounds. It has for example been applied for the construction of the fifth cyclopropane ring in the last step of a synthesis of the rotane 8 ... 

Acetylene-Expanded [n]Perkyclmes and Butadiyne-Expanded [n]Rotanes... 

Scheme 17. The main building blocks for butadiyne-expanded [n]rotanes and their per-methylated analogues...

This reaction sequence was also found to be convenient and versatile for preparing the potential synthetic precursors to permethylated 86 and spiro-cyclopropanated exploded [n]rotanes (Scheme 26) [48]. 

Scheme 25. Acyclic oligoynes for the preparation of expanded [n]rotanes...

Potential starting materials for the syntheses of exploded [n]rotanes via approaches B and C containing an even number of cyclopropane units may also be prepared by applying the Hay coupling procedure (Scheme 27) [48, 52]. 

When the acyclic dehydrohexamer 156 was oxidatively cyclized, an increased yield (49%) of the butadiyne-expanded [6]rotane 166 was observed, but the yield of the expanded [12]rotane 171 with a Cgo inner ring suffered from the fact that the corresponding acyclic dehydrododecamer 159 slowly decomposed in the syringe pump [48]. 

Scheme 31. Attempted synthesis of spirocyclopropanated butadiyne-expanded [n]rotanes from the acyclic precursors 150 and 151...

It is difficult to rationalize the low yield of exp-[4]pericycline 83. The fact that a cyclobutane ring is not easily closed cannot be the reason [4], since the corresponding protected exp-[4]pericyclinone 123 [39] and the Cgo-fullerene-annelated exp-[4]rotane 128 [38] were prepared without any problems. 

The most remarkable structural features of the planar cyclic mixed trisethyne-monobutadiyne pentaacetylenes 181 and 62 are their drastically bowed diyne moieties [18]. The acetylenic carbon atoms deviate from linearity by an average of 11.7° in 181 and even 13.4° in 62. The internal C-C-C angle is smaller for 181 (103.8°) than for 62 (109.2°). The disparity of the C-C bond lengths in the spirocyclopropane moieties of 62 is analogous to those observed in the expanded [n]rotanes 165-168. 

In view of the strain energy incorporated in a carbocyclic three-membered ring (28.1 kcal/mol [65]),thebutadiyne-expanded [ ]rotanes must be true high-... 

A more detailed investigation of the thermal behavior of the exploding [ ]rotanes by differential scanning calorimetry (DSC) measurements performed in aluminum crucibles with a perforated lid under an argon atmosphere revealed that slow decomposition of exp-[5]rotane 165 has already started at 90 °C and an explosive quantitative decomposition sets on at 150 °C with a release of energy to the extent of AH(jecomp = 208 kcal/mol. Exp-[6]rotane 166 decomposes from 100°C upwards with a maximum rate at 154°C and an energy release of AH(jg on,p=478 kcal/mol. The difference between the onset (115°C) and the maximum-rate decomposition temperature (125-136°C) in the case of exp-[8]rotane 168 is less pronounced, and AHjecomp 358 kcal/mol. The methy-... 

The fact that only ethylene and tetramethylethylene are evolved from exp-[8]rotane 168 and permethyl-exp-[6]rotane 173 upon thermal decomposition leads to the conclusion that the spirocyclopropane moieties in these expanded [n]rotanes fragment only externally and leave carbene moieties behind. Indeed, the MALDI-TOF mass spectra of several exp-[ ]rotanes show fragment ions with M minus 28. Thus, if this fragmentation in an exp-[n]rotane were to continue n times, a cyclic C carbon cluster would be left over. So far, however, a fragment ion with m/z = 480 corresponding to 182 has not been recorded in the mass spectrum of exp-[8]rotane 168 and it remains to be seen whether a Cgo cluster 183 will be detected in the mass spectrum of exp-[12]rotane 171 (Scheme 35). 

The MALDI-TOF mass spectra of the Cso-fullerene-annelated [3]- and [4]rotanes 127 and 128 also demonstrated that these molecules fragment at the spirocyclopropane units with successive loss of the fullerene moieties. Unfortunately, however, the peaks for cyclo-Ci and cyclo-C2o carbon clusters were not observed [38]. 

Acetylene- and Diacetylene-Expanded Cycloalkanes and Rotanes. 201 1 - 42 Diederich F, Gobbi L (1999) Cyclic and Linear Acetylenic Molecular Scaffolding. 20J 43 - 79 Gobbi L, see Diederich F (1999) 201 43 -129... 

Macrocyclic Structurally Homoconjugated Oligoacetylenes Acetylene-and Diacetylene-Expanded Cycloalkanes and Rotanes... 

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