Relay and sequential

Scheme 26.1 Cooperative (or synergistic), relay, and sequential catalysis (S.M., starting materials INT., intermediaries P., products CAT, catalyst).

In terms of relay and sequential metal-organo multicatalytic systems, these catalysts are most commonly used for 1,2 (aldol type) or 1,4 (Michael type) additions to suitable electrophiles. The most pervasive approach takes advantage of some metal-catalyzed process to generate a substrate for the organocatalyst. The examples illustrated in Scheme 26.16 show how chemical [94] or photochemical [95] metal-catalyzed oxidation of amines generates imine species that then undergo organocatalyzed 1,2 addition. 

Interlock and sequential control logic is performed by mechanical/electric relays and timers and the production train shutdown is performed by a combination of mechanical/electric relays and pneumatic relays. 

In this chapter, we present unique aspects of the rearrangement with a focus on (1) the production of carbanions under mild conditions, (2) the generation of synthetically valuable enol silyl ethers that are often the products, (3) the potential for incorporation of die Brook rearrangement in tandem and sequential anion relay processes, and (4) the utility of the rearrangement in generating chiral, configurationally stable carbanions. 

Schroeder, H. and Haslinger, E., Sequential analysis of oligosaccharide structures by selective NMR techniques. Part II. ID multistep-relayed C0SY-R0ESY, Liebigs Ann. Chem., 1, 751, 1993. 

Photophysical studies allow the measurement of rate constants for transmembrane electron transfer. The distributed kinetics observed in describing the decay of photovoltage across a BLM is consistent with a highly inhomogeneous disposition of donors and relays within the membrane [111, 112]. A typical value for the rate constant for electron transfer across a BLM (about 10 sec-1) would predict a spatial separation of about 10 A, whereas the thickness of the bilayer is usually about 40-50 A. This apparent discrepancy can be resolved if transmembrane electron transfer occurs by several sequential steps involving deeply buried redox sites, thus decreasing the operational tunnelling distance [113]. 

Scattered light collected by the FI.5 lens (f = 30 cm) is relayed to the photomultiplier tube via 1 mm slits, a 1 nm bandwidth interference filter and a polarization filter, to reduce background from flame luminescence. The PDP-11/34 computer instructs the A/D convertor to make a conversion every 100 vsec. The resulting digital data are stored sequentially in core memory. The memory is saturated at 16,000 temperature measurements, at which time the data are transferred to a hard disk memory. The data in this transfer constitute one time... 

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