Gilbert reagent

This Seyferth-Gilbert reagent is conveniently prepared through trifluoroacetylation and diazo transfer with concomitant detrifluoroacetylation. ... 

It is proposed that this reaction occurs via a mechanism similar to the Wittig Reaction In detail, deprotonation of the Seyferth-Gilbert reagent by potassium -butoxide generates a carbanion, which adds to the carbonyl group to yield an oxaphosphatane then subsequent elimination of dimethylphosphate leads to the formation of a vinyl diazo intermediate from which the vinyl carbene forms by evolution of nitrogen gas final 1,2-migration of the substituent on vinyl carbene yields the alkyne. An illustrative mechanism is displayed here. 

Of the methods available for potentiometrically estimating the amount of iodine bound by amylose, the differential method of Gilbert and Marriott36 is by far the most satisfactory for accurate work as it eliminates corrections for reagent blanks. In this method, the amylose solution and control solution form two half-cells connected by a salt-bridge, and the... 

The non-radioactive labeling utilizes fluorescence, chemiluminescence, or biotin/avidin interactions. Capillary electrophoresis with laser-induced fluorescence was first employed in PAL by Miller et al. [51]. Gilbert and Rando recently reported several biotin-containing heterobifunctional reagents and used them successfully [18] (Fig. 5). 

For a discussion of the mechanism with this reagent, see Hawari Davis- Engel Gilbert Grillcr J. Am. Chem. Soc. 1985, 107, 4721. 

We have already seen the bishydroxylation using 0s04 and NMO this time lead tetraacetate is used to cleave the diol and yield the aldehyde. The phosphorane (Me0)2P(0)CHN2 is named the Gilbert-Seyferth reagent. 8 It basically behaves like the phosphoranes in the Horner-Wadsworth-Emmons reaction described above, except that the olefin subsequently loses nitrogen, creating the desired triple bond (also see Chapter 10). 

Step 1 Conversion of an aldehyde to the corresponding terminal alkyne with Gilbert s reagent. 

The DNA sequencing chemistry begins with a base-modification reaction, the extent of which determines the frequency of DNA cleavage in the subsequent phosphate-elimination reaction. The number of bases modified in each molecule depends on the concentration of dimethylsulphate (G and G A reactions) and hydrazine (C T reactions) as well as the temperature and duration of the reaction. For speed and convenience the Maxam-Gilbert procedure makes use of temperature shifts and dilution to control the rate and extent of these reactions. The reagents are mixed at 0°C, incubated at 20°C for the required time and the DNA precipitated with cold sodium acetate and ethanol to slow down or halt the reaction. A fixed concentration of the different reagents is usually used so the main factor determining the extent of reaction is the time of incubation at 20°C. 

Figure 5-20. DNA sequencing by the Maxam-Gilbert method. End-labelled DNA is treated in four separate aliquots with chemical reagents which cleave specifically after A, G, C+Tand C. The fragments generated by partial chemical...

For a review of counterattack reagents, see Hwu, J.R. Gilbert, B.A. Tetrahedron 1989, 45, 1233. For a monograph that discusses most of the reactions in this section, see Stowell, J.C. Carbanions in Organic Synthesis, Wiley, NY, 1979. For a review, see Noyori, R., in Alper, H. Transition Metal Organometallics in Organic Synthesis, Vol. 1, Academic Press, NY, 1976, pp. 83-187. 

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