Ring events

The dynamical events that lead to the secular growth of the collision integrals are usually referred to in the literature as the ring events, in accordance with a description that can be given for them in terms of ring graphs. Statements (a)-(c) are based on phase space estimates of the type discussed here. Only in the case that the molecules are hard spheres or... 

Fig. 24. Some of the four successive binary collision events taking place among four particles (four-body ring events) that are responsible for the divergence of the four-body collision operator.

While generation of a Mn(V)oxo salen intermediate 8 as the active chiral oxidant is widely accepted, how the subsequent C-C bond forming events occur is the subject of some debate. The observation of frans-epoxide products from cw-olefins, as well as the observation that conjugated olefins work best support a stepwise intermediate in which a conjugated radical or cation intermediate is generated. The radical intermediate 9 is most favored based on better Hammett correlations obtained with o vs. o . " In addition, it was recently demonstrated that ring opening of vinyl cyclopropane substrates produced products that can only be derived from radical intermediates and not cationic intermediates. ... 

Each connection may be linked to one of the busses through one breaker, and in the event that one breaker is out of service or in need of maintenance, the connection may still be served through the two breakers to the other bus. The name of this arrangement comes from the fact that two connections are served by three breakers, so that there is an average of one and a half breakers per connection. This scheme is less complicated than the ring bus, with higher reliability, but is more costly. 

In the event, treatment of a rapidly stirred solution of 3 and sodium acetate in MeOH-tbO at 38 °C with PdCl2 results in the fomation of carpanone (1) in 46% yield. The ordered unimolecular transition state for the oxidative coupling reaction furnishes putative bis(quinodimethide) 2 stereoselectively. Once formed, 2 readily participates in an intramolecular Diels-Alder reaction4 to give carpanone (1). Two new rings and all five contiguous stereocenters are created in this spectacular sequential transformation.5... 

The first total synthesis of erythronolide B (1) by Corey stands as an event of great historical significance in synthetic chemistry it provides a powerful illustration of the utility of Corey s methods of macrolactonization and it demonstrates, in a particularly insightful way, the value of using readily accessible six-membered ring templates for the assembly of contiguous arrays of stereo-genic centers. 

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