Unambiguous preparation

Several mixed-metal clusters containing platinum and cobalt are known and some of them have been employed as methanol homologation catalysts.1 Among them, the title compound2 was first prepared unambiguously from the reaction of dichloro[l,2-ethanediylbis(diphenylphosphine)]platinum with sodium tetracarbonylcobaltate, Na[CO(CO)4]. The compound also may be prepared by the reaction of [l,2-ethanediylbis(diphenyl-phosphine)]bis(phenylethynyl)pIatinum with Co COJg.1... 

Doubts over the orientation of compounds such as those above can frequently be resolved by oxidation of the side chain, decarboxylation of the resulting carboxylic acid, iV-methylation, and comparison with the N-methyl oxo compounds 50 and 51. These compounds have been prepared unambiguously from methylamino aminopyridines by reaction with diethyl mesoxalate (Et02CC0C02Et), " followed by hydrolysis and decarboxylation. Thus 2-amino-3-methylaminopyridine (49) gave the... 

A related reaction employs bis(trimethylsilyl)peroxide in the presence of trimethylsilyl triflate. This procedure works efficiently with various aldehydes and ketones to give good yields of tetroxanes 48 (Equation 26) <2001COR601, 2002RMC113>. Alternatively, dispirotetroxanes can be prepared unambiguously by ozonolysis of cyclohexanone 0-methyl oximes (see Section 9.14.8.2.1) <2001COR601>. 

The most potent and biologically relevant hydroxylated metabolites derived from ARA, EPA, and DHA are formed via a sequence of enzymatic transformations and have stereochemicaUy defined structures with distinct R/S and Z/E configurations. Since these molecules are typically formed in very small quantities, the elucidation of their complete structure and stereochemistry is typically determined via a direct comparison and matching with stereochemicaUy pure materials and related stereoisomers prepared unambiguously via total synthesis [1]. These synthetic molecules also enable the investigation of the biological roles and mechanism of action of these hpid mediators. 

The derivative should be easily and quickly prepared in good yield by an unambiguous reaction, and be easily purified. In practice, this generally means that the derivative must be a solid, because of the... 

No unambiguous reactions of unfused azetes have been reported rather, the existence of transient azetes has been inferred from the observation of products which might reasonably be attributed to their further reaction. Separate discussion of reactivity and preparation is, therefore, inappropriate, and apart from a few general comments is deferred to Section 5.09.5.3. 

Tertiary pyrrolines (49, = 1) and piperideines (49, = 2) (if R = H and the enamine can exist in the monomeric form or if R = aryl) evidently possess an endocyclic -double bond (79,155,156). The stretching frequency of the double bond can be lowered to 1620-1635 cm by conjugation with an aromatic substituent. The double bond of an analogous compound with aliphatic substituents in position 2 may occupy either the endo or the exo position. Lukes and co-workers (157) have shown that the majority of the five-membered-ring compounds, traditionally formulated with the double bond in a position, possess the structure of 2-alkylidene derivatives (50) with an exocyclic double bond, infrared absorption at 1627 cm . Only the 1,2-dimethyl derivative (51) is actually a J -pyrroline, absorbing at 1632 cm . For comparison, l,3,3-trimethyl-2-methylene pyrrolidine (52) with an unambiguous exocyclic double bond has been prepared (54). 

Fry et al. prepared quaternary salts from 4-methyl- and 4-methyl-thio-quinazoline and found that the same cyanine dyes were obtained by suitable reactions of either salt. An unambiguous synthesis of the 4-methylthio salt (69) from l-methylquinazoline-4-thione (70) proved that both of the salts carried groups on N-1. 

This method is widely applicable to the unambiguous synthesis of quinoxalin-2-ones." It involves the intermediate preparation of a l,2,3,4-tetrahydro-2-oxoquinoxaline by the reductive ring closure of the o-nitrophenyl derivative of an a-aminoacid. These derivatives are formed readily from the aminoacid and an o-nitrohalogenobenzene. The final step of oxidation of the tetrahydro- to the dihydro-quinoxa-line is carried out with potassium permanganate or hydrogen peroxide. The preparation of 7-nitroquinoxalin-2-one illustrates the application of this synthesis ... 

The preparation of enamines of unsubstituted cyclic ketones is convenient and unambiguous in that only a single product results. Moreover, such enamines have found wide application as means of chain extension or ring formation. 

Because of the unambiguous reactive sites of monomers and the high chemo-and stereoselectivity of transition-metal-catalyzed coupling reactions, polymers prepared by transition metal coupling have predictable chemical structures. Functional groups can be easily and selectively introduced at the desired position within die polymer chains. Therefore, polymers widi specific properties can be rationally designed and synthesized. 

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