Unconventional access

A somewhat unconventional access to preceramic polymers containing silicon and boron has been reported by Schmidt et al. A borazine polymer and a silazane polymer are separately synthesized and dissolved in toluene, and then mixed together. The subsequent crosslinking of the borazine with the silazane components proceeds through hydrogen elimination and transamination reactions [54]. 

Occasionally, all of the traditional access routes have become occluded and the patient requires secure central access for chemotherapy. In these cases, unconventional access sites can be utilized based on a combination of image guidance and catheter/guidewire techniques that will result in a satisfactory catheter position. The unconventional access sites include recanalization of occluded pathways, catheterization... 

Mauro MA, Weeks S (1998a) Unconventional access. W. B. Saunders Co. 

This section is completed with a brief review of the synthesis and properties of this epimer (20) of the precursor of thiazole in bacteria. This pentulose is conveniently accessible by an unconventional route (Scheme 19). Methyl 2,3 4,6-di-O-isopropylidene-a-D-mannopyranoside, readily available from methyl ot-D-mannopyranoside, is converted to the ketonic glycoside by butyllithium in 91% yield, following a method first published by Klemer and Rodemeyer43 and scaled up by Horton and Weckerle.44 This was converted by means of lithium hydroxide in a water-ether mixture into 3,5-0-benzylidene-l-deoxy-D-eryf/iro-2-pen-tulose in 55% yield. Hydrolysis to the free pentulose (20) proceeded in 73% yield in aqueous acetic acid. This product was obtained as a syrup with a characteristic absorption band at 1705 cm 1 as a film. Thus, there is a fair proportion of the open-chain ketone under these conditions, as with the D-threo epimer.45... 

An important aim of this book, which complements a large number of books and reviews [3-32], is to make organic chemists familiar with the experimental methods (some being unconventional) that give access to a versatile and interesting class of compounds. 

The efficiency of /-elements in catalysis originates from unconventional electrophilic pathways. In contrast to rf-elements oxidative addition/reductive elimination sequences are not accessible. Instead, substrate adduct formation, ligand exchange and insertion reactions rule the mechanistic scenarios. Therefore, the main emphasis is put on the fine-tuning of the spectator ligand of the precatalyst. 

At present, the accessible physico-chemical properties have been studied mainly in liquid solution and the overall results provide evidence of their intrinsic high dipolar character. Moreover, compounds of type 1 may be ideal substrates for the study of their photophysical and other physical properties, especially for unconventional extended rr-systems 15-20, which are push-pull aza analogues of (E)-stilbene. Their capacity for specific physical behavior merits further exploration. 

Figure 1. Coronin domain organization and protein structure. A) Schematic of coronin domain organization. The p-propeller domain is approximately 400 residues in length and comprised of seven repeats (5 WD repeats and 2 unconventional repeats numbered and colored) flanked by short N- and C-terminal extensions (open). This is followed by the unique region (highly variable in sequence and length) and coiled-coil domain (approximately 35-50 residues in length). B) Crystal structures of mouse Coronin lA p-propeller domain (Appleton et al 2006/ PDB accession number 2AQ5) and coiled-coil domain (Kammerer et al 2005, PDB accession number 2AKF). The blades of the p-propeller are color-coded to match the schematic in A. The C-terminal extension (dark grey) associates with the underside of the blades. The coiled-coil domain of Coronin 1A (shown) forms parallel trimers, whereas the coiled-coil domains of some other coronins form dimers. N, amino terminus.

I am grateful to Jo Laird, Alan B. Thompson, Stefano Poll, C. Page Chamberlain, John T. Cheney, and John L. Rosenfeld for extensive discussions on this and related topics over the past two decades. I am especially grateful to reviewers Charles V. Guidotti and Stefano Poll for urging that my explanations for novel and unconventional concepts be made less cryptic, and that these explanantions should be less dependent on the treatments in earlier papers that may not be readily accessible to many readers. 

KeUey RE (2000) US Army special forces unconventional warfare doctrine Engine of change or reUc of the past . U.S. Naval War CoUege. http //handle.dtic.mi1/100.2/ADA378713 Accessed 30 June 2008. 

An unconventional modification of the Combes reaction was also used to access pharmacological interesting 3-formyl quinolines by treacling anilines with vinamidium salts. ... 

But, what would be an adequate system for a NMR large-scale quantum information processor Basically a system containing a large number of isolated qubits, perhaps thousands, in which the interaction between any pair of them could be controlled, and the state of each single qubit could be accessed by measurement. The need of such a system may sound hopeless, since conventional NMR sensitivity is limited to about 10 spins But that only means we have to look for something unconventional, perhaps combining the best aspects and capabilities of different techniques. 

Our initial studies uncovered a novel class of unconventional homoenolate nucleophiles accessible from the addition of an NHC to an unsaturated aldehyde. The umpolung addition of an alcohol across an enal to generate saturated esters has opened new possibilities for the development of useful acylatirai and oxidation reactions [99-106]. 

Dunach and coworkers have reported an unconventional method to access thiolactones. In their work, BF3 OEt2 efficiently catalyzes the isomerization of thionolactones (68) to the corresponding thiolactones (69). This process is quite general in substrate scope and gives the requisite products in good yields (Equation 43)... 

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