Aliphatically Clamped Alkenes

Introduction of an aliphatic clamp in the ( )-position of alkenes leads to twisted double bonds and therewith to helical alkenes like 55-65. 

Scotts viewpoint can be applied also to the ( )-2-cyclooctene-type molecules 64 and 65, synthesized by Nakazaki . The octant rule predicts the absolute configuration (S) at C atom 5 for the minus rotating enantiomer of bicyclo[3.3.1]non-l(2)-ene (64) ([ ] = —237, in ethanol, [ajo = —259, in CHCI3) . For the counterclockwise rotating enantiomer of (/ )-(—)-D2-bicyclo[8.8.0]octadec-l(10)-ene (65), which was prepared only in low optical purity ([a]o = —2.3, in dioxane) , the (R)-configura-tion is predicted by the octant rule. 

A rotation value of = 4-46.9 (CHCI3) has been found for [10.10]betweenane 58. The R-configuration of the (+)-modificatlon has been correlated with a negative Cotton effect and compared with the Cotton effect of the 1,2-disubstituted ( )-cycloalkenesThe syntheses of [ll.ll]betweenane 59 and of the thia derivative [10.7]betweenane 60 have been carried out, but no chiroptical investigation has been undertaken hitherto. Recently, Nakazaki reported on the synthesis of (/ )-(-(-)-[10.22]betweenane (62) with an optical rotation of [a] = 4-27.2, [0)220 = +128 . 

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Fig. 28. Examples of aliphatically clamped alkenes 55-65. Octant projections of (S)-( -(- )-64, (KK— 65 according to Scott ...

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