Other Methods of Synthesis

Under these methods of synthesis of pyrrolo[l,2-a]quinoxalines, we include methods based either on condensed derivatives of quinoxaline (a) or on compounds containing neither a pyrrole ring nor a quinoxaline system (b). In method (b), the pyrroloquinoxaline system can be formed with the initial formation of the pyrrole ring (b-7) or the quinoxaline system (b-IT). In this review, we examine only the second version (h-IT). 

Economically favorable and ecologically harmless methods, which are in most cases one-pot tandem processes, occupy a special position among methods for the synthesis of condensed heterocyclic compounds. 

As seen from the retrosynthetic analysis of the strucmre presented below, the simplest and most accessible reagent for the synthesis of pyrrolo[ 1,2-a]quinoxalines is 1,2-DAB. If the aim is to synthesize a derivative of pyrrolo[l,2-a]quinoxaline from 1,2-DAB, the second reagent must be a compound with at least five carbon atoms having functional centers capable of reacting with the amino groups of the 1,2 DAB at positions 1, 2, and 5 (Fig. 3.6). 

The second path seems more likely since during the reaction of the hydroxy-diketone with 1,2-DAB in a 15 1 mixture of ethanol and acetic acid and subsequent oxidation, a mixture of compound 120 and the quinoxaUne derivative 125 in a ratio of 2 5 is formed. 

The iV-oxides not only of quinoxalines but also of 1,4-benzodiazepines can serve as excellent 1,3-dipoles in the synthesis of derivatives of pyrrolo[l,2-fl]quinoxa-lines. For example, the reaction of chlorodiazepineoxide 133 with dimethyl acetylenedicarboxylate takes place by a scheme of 1,3-dipolar addition with the 

5- anhydro-D-mannitol (styracitol) with Fenton s reagent, with the formation of D-glucosone, characterized as D-glucose phenylosazone, has been described70 oxidation of these anhydrohexitols with hypobromite gave 

5- anhydro-3-oxo-D-grZycero-hexulose, identified as the 2,3-phenylosazone. Bayne, Fewster and Mitchell16 obtained D-glucosone, characterized as 

---

Lewis acids such as zinc triflate[16] and BF3[17] have been used to effect the reaction of indole with jV-proiected aziridine-2-carboxylate esters. These alkylations by aziridines constitute a potential method for the enantioselective introduction of tryptophan side-chains in a single step. (See Chapter 13 for other methods of synthesis of tryptophans.)... 

The anhydrous halides, chromium (ITT) fluoride [7788-97-8], CrF, chromium (ITT) chloride [10025-73-7], CrCl, chromium (ITT) bromide [10031-25-1], CrBr, and chromium (ITT) iodide [13569-75-0], Crl, can be made by the reaction of Cr metal and the corresponding halogen at elevated temperatures (12,36). Other methods of synthesis for the haUdes are also possible (36—38). All of the haUdes have a layer stmcture and contain Cr(III) in an octahedral geometry. They are only slightly soluble in water but dissolve slowly when Cr(II) or a reducing agent such as Zn or Mg is added. 

I.3.3.3.3.I.I.4. Other Methods of Synthesis of Allylboron Reagents Lacking Stereogenic... 

DMAP has been found to improve the coupling reaction in solid phase peptide synthesis (4). Polypeptides synthesized via the DMAP-DCC method were found to be of higher purity compared to other methods of synthesis. In polymer chemistry, DMAP has been used for hardening of resins and in the synthesis of polyurethanes, (5) polycarbonates, (6) and polyphenyleneoxides (7) ... 

Borylation of hydroxyalkylphosphines in the absence and presence of additional reagents is the most effective and universal method of synthesizing the boroxyalkyl derivatives of phosphorus, providing a wide variety of structures. Among other methods of synthesis of boroxyalkylphosphines from aminomethylphosphines is of special interest. This is illustrated in... 

Other Methods of Synthesis Intramolecular cyclic hydroxyamino-alkynes (188) and (189), depending on the relative position between the hydroxy-lamino group and acetylenic fragment, leads to five-(190), six-(191), and seven-(192) membered cyclic nitrones (Scheme 2.67) (348-350). 

Other Methods of Synthesis of Nanostructured MgH than Ball Milling... 

As in the previous example, the final product is a racemate from which the levorotary isomer is isolated. Other methods of synthesis were suggested later on [9,10],... 

Other Methods of Synthesis. Huge quantities of aromatics are synthesized by thermal reforming and by catalytic and thermal cracking of middle distillates and... 

Table 6). The majority of the complexes in Table 6 are obtained by the reaction of boranes with ligands. Some other methods of synthesis are illustrated by equations (11)—(14). 

Other methods of synthesis are widely reviewed by Dayagi and Degani.2 However, it must be observed that few Schiff bases commonly used as ligands have been prepared and characterized in the uncomplexed state, since the corresponding metal complexes have been directly obtained by other procedures. For example, many metal complexes containing salenH2 may be obtained directly by reaction between metal ions, salicylaldehydes and ethylenediamine.3... 

Whereas no other methods of synthesis of 21 and its derivatives are currently known, the nucleophilic addition of telluride anion to 1,5-diorganylpentadi-1,4-ynes may be considered a promising approach, based on the finding that sodium telluride reacts smoothly with monosubstituted alkynes, giving rise to divinyltellurides (89MI1). 

Specific procedures for the synthesis of M0CI4, MoCl, and M0CI2 are described in the sections that follow. Other methods of synthesis are also summarized in these sections. Procedures for the synthesis of M0CI5 have been given in Inorganic Syntheses 7, 167 (1963) and 9, 135 (1967). The industrial method is the direct chlorination of metal and is recommended in some laboratories.12-18 A convenient laboratory technique is the liquid-phase reaction system that uses refluxing thionyl chloride and molybdenum (VI) oxide.14... 

Although the vast majority of Group IB metal heteronuclear clusters have been synthesized using one of the generally applicable rational preparative procedures outlined in Sections II,A,1 and II,A,2, a number of such species have been obtained via routes for which the nature of the product cannot be predicted in advance or via procedures which have not been widely used. These other methods of synthesis are outlined in this section. 

Binary technologies are also acknowledged however, the development of other methods of synthesis is not excluded (the more steps there are involved in synthesis the more difficult it is to control the process). An alternative is to search for compounds either used or synthesized already. From the groups of highly toxic chemicals these could be fluorophosphorylcholines (unstable) or toxic silatrans. In the group of medicaments, there are also highly toxic chemicals... 

Silver-catalyzed silylene transfer was developed as a mild and efficient method for silacyclopropene 48 synthesis. Employing low temperatures for the transfer improved diastereoselectivity and substrate compatibility compared to other methods of synthesis (Equation 5) <2004JOC4007>. 

Dodecacarbonyltriruthenium, Ru3(CO)i2, can be prepared in good yields by the usual methods, but these require the use of high-pressure equipment. Recently, however, several syntheses of this carbonyl at atmospheric pressure have been reported. -4 xhe carbonylation of [Ru(CO)3Cl2]2 in the presence of zinc does not give satisfactory yields of Ru3(CO)i2. Also it requires the previous isolation of [Ru(CO)3Cl2]2. This compound can easily be obtained from Ru3(CO)i2, but other methods of synthesis are not very convenient. 

Quinone Oximes.—The most interesting of the derivatives of quinones are the oximes. As stated in the discussion of the ketone structure for quinones one of the proofs for this constitution is the fact that benzoquinone forms both a mono-and a di-oxime when treated with hydroxyl-amine. The mono- oxime of benzoquinone would have the structure as written below and as given on page 638. Now as previously mentioned, (p. 628), para-nitroso phenol, which is made by the action of nitrous acid upon phenol and the constitution of which is established by other methods of synthesis, (p. 627), proves to be one and the same compound with this mono-oxine of para-benzoquinone, the constitution of which is likewise established by the above reaction of hydroxyl amine upon quinone. This is explained by a rearrangement as shown in the following ,... 

---