Silanes strained cyclic

Ring strain in small cyclic alkanes and silanes... 

Table 3.27. Symmetry, bond lengths Raa and Rah, bond angle 6 hah and theoretical strain energy (TSE) for small cyclic alkanes (A = C) and silanes (A = Si), with corresponding geometrical variablesT of acyclic (C2V) propane and...

Coordination to alkynes distorts the triple bond character nearer to that of a double bond, decreasing the linearity. Utilization of the coordination effect makes it feasible to prepare cyclic alkynes whose synthesis is difficult to achieve. Highly strained cyclooctyne can be prepared by coordination. As an example, starting from (R)-pulegone, three of the four rings of the epoxydictymene skeleton 152 were constructed by the consecutive Lewis acid-promoted Nicholas reaction of allylic silane 149 to form 150, and the intramolecular Pauson-Khand reaction of 151. The total synthesis of (+)-epoxydictymene 153 from 152 has been achieved [38]. 

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