Propynes carbon atom reactions

We won t study the details of this substitution reaction until Chapter 11 but for now can picture it as happening by the pathway shown in Figure 8.6. The nucleophilic acetylide ion uses an electron pair to form a bond to the positively polarized, electrophilic carbon atom of bromomethane. As the new C-C bond forms, Br- departs, taking with it the electron pair from the former C-Br bond and yielding propyne as product. We call such a reaction an alkylation because a new alkyl group has become attached to the starting alkyne. 

The reactivity of OsHCl(CO)(P Pr3)2 toward alkynols depends on the substituents at the C(OH) carbon atom of the alkynol (Scheme 14).47 The reaction with 2-propyn-1 -ol initially affords the alkenyl compound 6s(CI I=CI ICII2OI I)Cl(CO) (P Pr3)2 in 85% yield, as a result of the anti-addition of the Os—H bond to the carbon-carbon triple bond of the alkynol. In chloroform-df solution this complex decomposes to a mixture of products, containing the derivatives OsCl2(CHCH=CH2) (CO)(P Pr3)2 and 6s(CHCHCH6)Cl(CO)(P Pr3)2 (Eq. 5). 

Acetylene is the most widely used alkyne. Alkynes undergo the same reactions as alkenes. Because a triple bond coimects the two carbon atoms, addition of an atom initially forms a double bond. The addition of a second atom converts the double bond into a single bond. For example, hydrogenation of propyne to propane is represented as ... 

Template reactions between malonaldehydes and diamines in the presence of copper(II), nickel(II) or cobalt(II) salts yield neutral macrocyclic complexes (equation 15).99-102 Both aliphatic102 and aromatic101 diamines can be used. In certain cases, non-macrocyclic intermediates can be isolated and subsequently converted into unsymmetrical macrocyclic complexes by reaction with a different diamine (Scheme ll).101 These methods are more versatile and more convenient than an earlier template reaction in which propynal replaces the malonaldehyde (equation 16).103 This latter method can also be used for the non-template synthesis of the macrocyclic ligand in relatively poor yield. A further variation on this reaction type allows the use of an enol ether (vinylogous ester), which provides more flexibility with respect to substituents (equation 17).104 The approach illustrated in equation (15), and Scheme 11 can be extended to include reactions of (3-diketones. The benzodiazepines, which result from reaction between 1,2-diaminobenzenes and (3-diketones, can also serve as precursors in the metal template reaction (Scheme 12).101 105 106 The macrocyclic complex product (46) in this sequence, being unsubstituted on the meso carbon atom, has been shown to undergo an electrochemical oxidative dimerization (equation 18).107... 

Cycloaddition. The photochemical reactions of 1,2-dimethylcyclobutadiene tri-carbonyliron with acetylene gives o- and p-xylene while propyne gives 1,2,3- and 1,2,4-trimethylbenzene and but-2-yne forms 1,2,3,4- and 1,2,4,5-tetramethyl-benzene. Preferential formation of these isomers is best rationalized in terms of Scheme 5 in which initial carbon-carbon bond formation occurs between the acetylene and a carbon atom of the cyclobutadiene ring bearing a methyl group. The intermediacy of complexes structurally analogous to (38) in cycloaddition reactions... 

A series of cationic, strapped, r)6 ri1 ri1-arene complexes of ruthenium(II) (82) containing both carbon and phosphorus as the auxiliary atoms has been obtained by a coupling reaction of the iminophosphorane complexes 83 with an excess of 1, l-diphenyl-2-propyn-l-ol, the p-cymene in 83 being displaced by one of the phenyl... 

Directed Pauson-Khand reactions , giving only one of two possible regioisomers, occur when the carbon chain of the alkene is attached to a nitrogen or sulphur atom. Thus treatment of the propyne-dicobalthexaarbonyl complex with the thioether 491 gave solely the cyclopentenone 492. ... 

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