Unusual approach

An unusual approach to the lumazine nucleus was found in the photochemical transformation of 6-azido-l,3-dimethyluracil (289) with various amino compounds (78JA7661). Irradiation of (289) in the presence of ethyl a-amino acid esters forms 7-substituted 7,8-dihydrolumazin-6-ones (288), and with a-aminoketones 6-substituted 7,8-dihydro-lumazines (290) are formed (equation 103). 

An unusual approach toward the preparation of a-bisphospho-nates began by treatment of an oxime with a phosphorus nucleophile (trialkyl or dialkyl phosphite) and phosphorus oxychloride (as promoter).354 The oxime undergoes a Beckman rearrangement the phosphorus nucleophile attacks the intermediate cation leading to an imine, which is then further attacked by the phosphorus nucleophile to give the a-bisphosphonate (Equation 3.21). 

An unusual approach is the isomerization of a methyl-substituted 1,2,3-buta-triene to a vinylallene by stoichiometric deprotonation with wBuLi-TMEDA and reprotonation [83]. With an ether substituent on the butatriene a similar reaction is possible with KOtBu in DMSO [84], while a phenyl-substituted butatriene reacted spontaneously in CHC13 [85]. 

The next step is an unusual approach to making an ester via an Sn2 reaction. We usually make esters by the reaction of alcohols with activated carboxylic acid derivatives like acyl chlorides, or anhydrides as we have just seen. We do not particularly want to have to convert the carboxylic acid (X) into a more reactive... 

Many of the compounds of this type have been prepared by interaction of cumulene ylides witli heterocumulenes and these are covered in a review by Bestmann <77AG(E)349>. The oxetane system 5 results from reaction of Ph3P=C=C=S with aryl isocyanates, ArNCO <77AG(E)349>. An unusual approach to an oxetane ylide is the reaction of DMAD with CO2 and two equivalents of methyl phosphite which gives 6 <81CC607>. 

Finally, an unusual approach to pyrrolo[2,3- pyrimidines is seen in Equation (40). The dimethyluracil 113 is presumed to form the A -oxide at the exocyclic nitrogen atom. This then undergoes a [2,3]-sigmatropic rearrangement followed by a [3,3]-sigmatropic rearrangement, tautomerization, and cyclization to give 114 <200581164>. 

An unusual approach to the synthesis of furo[3,4-,7lpyrimidinones is shown in Equation (116). Stmcture 323 is transformed into 324 by heating the compound neat in an oil bath in near-quantitative yield <2000BML175>. 

A somewhat unusual approach is encountered when high-speed motion picture cameras of the Hycam type are used as a streak camera. This is accomplished by filming through the camera s viewfinder which bypasses the prism system that normally cuts up the scene into frames or pictures. After nearly one-fourth of the film has run through the camera the voltage-controlled rate of film travel is reasonably steady and can be used for velocity measurements. 

Streatfeild, Dominic. Cocaine An Unauthorized Biography. New York Picador, 2003. The author, a documentary film producer, has translated some of his techniques to the print medium. This book takes the unusual approach of... 

I The second purification procedure we examine illus- Vri trates an unusual approach to the purification of a membrane-bound protein. The lactose carrier protein of E. coli is normally tightly bound to the plasma membrane. This protein is involved in the active transport of the dissaccharide lactose across the cytoplasmic membrane. When lactose carrier protein is present, the intracellular concentration of lactose can achieve levels 1,000-fold higher than those found in the external medium. Ron Kaback devised a simple yet elegant procedure for the purification of this protein. 

Starting from 1,5-anhydro-2,3,4-tri-0-benzoyl-6-deoxy-D-ura >/ o-hex-1 -enitol (48), an unusual approach to the synthesis of disaccharides of serogroup A and D has applied the allylic rearrangement glycosylation procedure of Ferrier [127] to obtain an a-D-< rj//zTO-hex-2-enopyranosyl residue in the disaccharide 49a. Reduction of the 2-enopyranose double bond gave both the paratose (ribo) 49b and tyvelose (arabino) 49c products [28]. 

The third and unusual approach to C-l-C-substituted glycals, which involves simultaneous introduction of a C-nucleophile at C-l and elimination, is illustrated in Scheme 14. Treatment of ether- or acetal-protected glycopyranosyl chlorides with methyl-, butyl-, or phenyl-lithiums in THF under argon at room temperature or below, gives moderate yields of the C-l substituted compounds.145... 

Since the consumers of the TEM technique come from a wide variety of backgrounds, interesting variations of sample preparation are introduced all the time. Some examples of unusual approaches are as follows [8] ... 

A small number of stable compounds have been produced with substituents at both peri and end positions. The first such system was the product of repeated application of a zirconium-mediated cyclization to phthalate ester 35, leading to the heavily substituted pentacene 36 in 11 steps (Scheme 3.8) [51]. Little discussion of the properties of this pentacene derivative was presented, but it was soluble and stable enough for complete characterization. This unusual approach to the synthesis of pentacene is one of the few to yield such high substitution. 

COMPLEX VARIABLES, Francis J. Flanigan. Unusual approach, delaying complex algebra till harmonic functions have been analyzed from real variable viewpoint. Includes problems with answers. 364pp. 5)4 x 8)4. 61388-7 Pa. 7.95... 

Although the preparation of macrocycles often involves improved methods, several efforts have been made particularly to improve synthetic approaches. In an unusual approach, 4,13-diaza-l 8-crown-6 was converted to its bis(methyl) aminal. The CH3OCH2N< side-chain residues are labile and permitted a Mannich-type reaction with various bis(phenols) under acid catalysis <1995JOC4912>. Two of the resulting structures are shown as 20 and 21 in Figure 21. Not all phenols proved to be successful substrates for this reaction but compound 20 was formed in 25% yield. 

However, relatively less use of the reaction appears to have been made in the preparation of the higher terpenes, but some notable exceptions to this are the use of a Moffatt oxidation as a key step in an unusual approach to hydrazulene-based sesquiterpenes, (42) to (43 equation 17), and the use of the Swem variation in the gibberrellin synthesis (44) to (45 equation 18). 

This is a rather unusual approach to dieting, I think you ll agree. UCLA has had tremendous success, whether a person wants to lose 10 pounds or 100. To lose very large amounts of weight, obese individuals have followed the program for up to a full year. 

A further example of this unusual approach is provided by the reaction of phenylpropargyl alcohol with an aryl Grignard reagent followed by SOCI2 to give the product 123 (Equation 21) <2005BML2057>. 

In the following section the stochastic formulation of the encounter rate developied above will be used as the basis of a molecular theory of singleparticle motion by the expedient of associating one of the particles with a solvent molecule. This is an unusual approach because the quality of interest, namely, itself, apjjears in the encounter rate. The problem must be solved by closure. 

One unusual approach to the synthesis of pyrazoles 509 from azo compounds 510 under phase-transfer conditions for the generation of dichloro-carbene was proposed by Baldoni ef al. (89JHC241). 

Two unusual approaches to TLC of amoxicillin and other penicillins are the use of silica gel impregnated with tricaprylmethylammonium chloride with a methanol/water mobile phase [111], and the use of micellar solutions as mobile phase [112]. The latter was reported to give better separation of penicillins and their degradation products than organic mobile phases. 

In an unusual approach, Rauchfuss and coworkers were able to show tliat Fc3(CO),2 reacts not only with free thiophenes -as described in the preceding section- but also with the n activated thiophene in the rhodium complex Cp Rh(r -T), to yield predominantly a bimetallic product containing a ferrole unit K-bonded to Rh. The reaction was shown to proceed via a stable intermediate containing the T ligand simultaneously bonded t) to Cp Rh and t) to a Fe(CO)4 fragment both complexes... 

A single example of this unusual approach is provided by treatment of the 4-sulfonyloxycrotonates... 

---