Strain-driven reactions

A further method of producing amorphous phases is by a strain-driven solid-state reaction (Blatter and von Allmen 1985, 1988, Blatter et al. 1987, Gfeller et al. 1988). It appears that solid solutions of some transition metal-(Ti,Nb) binary systems, which are only stable at high temperatures, can be made amorphous. This is done by first quenching an alloy to retain the high-temperature solid solution. The alloy is then annealed at low temperatures where the amorphous phase appears transiently during the decomposition of the metastable crystalline phase. The effect was explained by the stabilisation of the liquid phase due to the liquid—>glass... 

The lactonization of a crowded hydrocoumarin (78), or more generally reactions driven primarily by strain release, can be regarded... 

These reactions are driven by a combination of factors, including a loss of ring strain or the release of a volatile olefin such as ethylene. They can also be kinetically controlled by the formation of a less reactive carbene complex. An important feature of RRM is the catalytic transfer of stereocentres from the corresponding substituted carbocycles, i.e. the chirality embedded in the carbocyclic starting material is completely transferred to the product side chain. This allows chirality to be introduced by means of side chains at the carbocycle. Synthetically, this... 

A pinacol rearrangement driven by the release of the ring strain in a four-membered ring is shown in Scheme II/3. The exclusive acyl migration from II/7 to II/8 is remarkable [3]. Similar reactions have been reported in literature... 

Ring opening metathesis polymerization, which has been known since the discovery of the alkene metathesis reaction, has been given the acronym ROMP in recent years. In fact, the ROMP reaction was the first observation made in alkene metathesis chemistry, while the discovery of the exchange reaction in equation (1) actually occurred later. Acychc diene metathesis (ADMET) polymerization (equation 3) has only recently been shown to be a viable method for polymer synthesis, and it has been termed ADMET polymerization. ROMP reactions are driven by the release of ring strain from the monomer, while ADMET polymerization is driven by a shift in the equilibrium caused by the removal of one of the reaction products. 

A number of catalytic reactions involve CC bond cleavage, often driven by strain. For example, " biphenylene can be converted to tetraphenylene with Ni(cod)(PMe3)2 at 100 °C or Pt(PR3)3 at 120 °C (equation 14). In the Pt case, a series of intermediates could be isolated that suggest a pathway involving double oxidative addition of the biphenylene CC bond, as in the stoichiometric reactions previously discussed, followed by double reductive elimination to give the product. 

When certain cycloalkanes are used in metathesis reactions, ring-opening metathesis polymerization (ROMP) occurs to form a high molecular weight polymer, as shown with cyclopentene as the starting material. The reaction is driven to completion by relief of strain in the cycloalkene. 

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