In situ trapping

Tliis beaelicial effect of additions has been observed in tliat tlie yields in tlie tandem vet in situ trapping of tlie reactive ei tlie addition of Et2Zn to 44 wbet Higli enantioselectivities 183-... 

SYNTHESIS OF ORTHO SUBSTITUTED ARYLBORONIC ESTERS BY IN SITU TRAPPING OF UNSTABLE LITHIO INTERMEDIATES 2-(5,5-DIMETHYL-l,3,2-DIOXABORINAN-2-YL)BENZOIC ACID ETHYL ESTER... 

The in situ trapping of unstable lithio-intermediates as a way of circumventing the above... 

As first described by Krizan and Martin,6 the in situ trapping protocol, i.e., having the base and electrophile present in solution simultaneously, makes it possible to lithiate substrates that are not applicable in classical ortho-lithiation reactions.7 Later, Caron and Hawkins utilized the compatibility of lithium diisopropylamide and triisopropyl borate to synthesize arylboronic acid derivatives of bulky, electron deficient neopentyl benzoic acid esters.8 As this preparation illustrates, the use of lithium tetramethylpiperidide instead of lithium diisopropylamide broadens the scope of the reaction, and makes it possible to functionalize a simple alkyl benzoate.2... 

Tetrahydrocarbazoles have been prepared in one-flask syntheses from indoles, ketones and maleic anhydride, with acid catalysis. The reactions involve a condensation of the indole 121 with the ketone or aldehyde, followed by in situ trapping of the vinylindole 122 with maleic anhydride to afford tetrahydrocarbazoles 123 after double bond isomerization <96T4555>. 

Several attempts to take advantage of the intermediate boron enolate to achieve tandem conjugate addition-aldol reaction have been proposed [71]. Recently, Chandrasekhar [72] reported the addition of triethylborane to methyl vinyl ketone followed by the in situ trapping of the enolate by aromatic aldehyde (Scheme 26). 

The ring fused pyrroles 480 have been prepared by in situ trapping of the meso-ionic l,3-oxazol-5-ones (479) with alkynes. This 1,3-dipolar cycloaddition was found to be regiospecific when phenyl acetylene was used as 1,3-dipolarophile, the only products being 480, R = H or MeO, R = Ph, R2 =... 

Table 2. Enantioselective Dcprotonation of 4-Substituted Cyclohexanones 1 in THF with in situ Trapping of the Intermediate Lithium Enolate with (CH3)3SiCl at — 78°Ca-b 13-14-24-2g-3S-37-55-55a...

Table 4. Asymmetric Deprotonation of 1 with Chiral Lithium Amides in THF and in situ Trapping of the Lithium hnolatc with (CH3)3SiCl...

H. Matusiewicz and M. Mroczkowska, Hydride generation from slurry samples after ultrasonication and ozonation for the direct determination of trace amounts of As (III) and total inorganic arsenic by their in situ trapping followed by graphite furnace atomic absorption spectrometry, J. Anal. At. Spectrom., 18, 2003, 751-761. 

The compatability of LiTMP and hexafluoracetone allows the application of the in situ trap technique to form the carbinols 501 and 502 in useful yields (83JOC4156). Similar results were observed with TMSC1 as the electrophile. 

The preceding scheme also shows how a controlled thermal decomposition of the metallated thioimidoesters (enaminates (4)) by in situ trapping by an organometallic of the ketenimines (5) formed by loss of MeSLi allows a very direct route to ketones [381, 382]. An example of this application is given over. 

Similar elimination from 1,3,2-dioxathiolane -oxides (cyclic sulfites) has been studied and used along with an in situ trap (DBU/TMSC1) to obtain a tautomeric equivalent of a-oxocarboxylic acid ester (Scheme 14)... 

The vapor can be atomized in inert gas-hydrogen diffusion flames, in narrow-bore quartz tubes electrically heated or heated over an air-acetylene flame, and in plasmas. Additionally, the atomizer can act as a vapor preconcentration medium just before atomizing. This is what happens in graphite furnace atomizers (in situ trapping) or on silver or gold wires for direct amalgamation of mercury. 

Scheme 13 In situ trapping of vinyl ether and enamine structures in the mixture of uncontrolled thermal decomposition of NMMO...

Scheme 14 Uncontrolled thermal decomposition of NMMO in situ trapping of vinyl ether structures in the gas phase of the reaction...

An improved method for the preparation of selenoaldehydes from the reaction of bis(N,N-dimethylcarbamoyl-seleno)methanes with stannic chloride led to formation of a 2H-selenin by in situ trapping with 2,3-dimethyl-l,3-butadiene (cf. Equation 69) <2006HAC125>. 

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