Helical primary structures of 1,2-spiroannelated five-membered rings: attempted synthesis of (±)-tetraspiro[4.0.0.0.4.3.3.3]heneicosane

Ring Expansion of Cyclobutylmethylcarbenium Ions to Cyclopentane or Cyclopentene Derivatives and Metal-Promoted Analogous Rearrangements

“…Another application of this method involved the synthesis of pseudohelical hydrocarbons of four- and five-membered rings (Scheme ) . Addition of 1-lithiocyclopentene 107 and 1-lithiocyclobutene 110 , respectively, to dispiroketone 106 led to allylic alcohols 108 and 111 in 82 and 64% yield, respectively, which were regio- and stereoselectively converted into cyclopentanones 109 and 112 by reaction with 1.2 equiv of chloramine-T and 1.2 equiv of ZnBr 2 in acetonitrile at room temperature in 82% and 66% yield, respectively.…”

“…A last example involves the synthesis of pseudohelical hydrocarbons of four- and five-membered rings . A sequential ring enlargement via a high-temperature methylenation, an epoxidation, and a lithium iodide-induced rearrangement proved necessary to synthesize complex cyclopentanone 460 (Scheme ).…”

Polytriangulane

“…While the first member of the higher triangulanes, [4]triangulane, was prepared in racemic form in 1990, 9 its first enantioselective synthesis was accomplished by de Meijere et al 5 in 1999. Within a few years, de Meijere and co-workers were then able to synthesize enantiomerically pure compounds of this type up to [15]triangulane, 1,2 which is the largest member of all σ-helicenes known to date. Here, we go a step further and report on the theoretical and computational exploration of an infinite extension of a C 2 -symmetric, helical [n]triangulane that we name polytriangulane.…”

“…In constructing triangulanes beyond [3]­triangulane, , linear, helical, and branched isomers ensue (Scheme ). The helical [ n ]­triangulanes belong to the σ-helicene family, which also encompasses the spiro-cyclobutanes, , spiro-cyclopentanes, , oligotwistanes, , and helical diamondoids such as [1(2)­3]­tetramantane (Scheme ). The [ n ]­triangulanes, oligotwistanes, and diamondoids have no internal rotational degrees of freedom and therefore occur as highly rigid, solitary structures.…”

“…The σ-helicenes are inherently chiral, and their optically rotatory powers mirror their strain energies; thus, the helical [ n ]­triangulanes display the largest optical rotations of any alkane of comparable molecular weight. ,,,, This increase in the Cotton effect has been rationalized on the basis of the Walsh orbital model of the bonding in cyclopropane, in which the strained carbon–carbon bonds exhibit enhanced C methylene p -orbital contributions. , Remarkably, the rotatory power of rigid σ-helicenes , (as well as π-helicenes) increases monotonically with helix length, while it uniformly decreases in this manner for the conformationally flexible polyspirocyclobutanes and polyspirocyclopentanes. − …”