Ketones alkynes and

Reduction of unsaturated organic substrates such as alkenes, alkynes, ketones, and aldehydes by molecular dihydrogen or other H-sources is an important process in chemistry. In hydrogenation processes some iron complexes have been demonstrated to possess catalytic activity. Although catalytic intermediates have rarely been defined, the Fe-H bond has been thought to be involved in key intermediates. 

A series of 3-hydroxybut-4-ynoic esters (319) has been prepared from alkynic ketones and bromoacid esters in the presence of zinc (61AP234). Ring closure to the pyran-2-one occurs in a mixture of acetic and sulfuric acids. The preparation of 4,6- and 3,4,6-substituted pyranones is possible by this route, the substituents being different or identical, and as such is complementary to the alkynic route to the 3,6-disubstituted compound (57JA2602). 

Recently, the role of metal cations has been studied in detail [13, 14], it having been observed that when A1 or Mg cations are added to the reaction medium, they have a strong influence on the reduction process of alkynes, ketones and halides, and in most cases this leads to a complete change of the mechanism. In contrast, when ions are supplied to the reaction medium by oxidation of the anode during electrocarboxylation, they show no effect on the cathodic process. Hence, it appears that metal cations produced by the consumable anode in undivided cells are intercepted and complexed by the carboxylated products before they can reach the cathode. Therefore, the cathodic process can occur in a medium without free metal ions. 

A number of structurally diverse ketones have been reduced using BINAL-H. Some of the results are summarized in Table 1. Aryl alkyl ketones, alkynic ketones, and a, -unsaturated ketones are reduced to alcohols with good to excellent % ee, while aliphatic ketones give products with lower optical purities. The asymmetric reduction of a number of acylstannanes with (7) gives synthetically valuable a-alkoxystannanes with high optical purities after protection of the initially formed unstable alcohols as their MOM or BOM ethers. ... 

In general, synthesis of 4-isoxazolines is accomplished via three routes 1,3-dipolar cycloaddition of nitrones to alkynes or by the oximation of a,i -ethylenic ketones, a-alkynic ketones and aldehydes or from the selective reduction of isoxazolium salts. The nitrone (262) underwent tandem cyclo-addition-[2,3]sigmatropic rearrangement with allenyl sulfoxide (263). And it resulted in 4-isoxazoline (264) (Equation (46)) <89TL663>. 

Compound 11 is an alkyne-ketone and, because the carbonyl has the higher priority, it is named as an yn-one. Compound 11 is a heptyne derivative, so it is named as a heptynone—specifically, heptyn-2-one. If the carbonyl carbon is at C2, the first carbon of the C=C unit is at C4, so 11 is hept-4-yn-2-one. There are no E- or Z-isomers for the alkyne unit. 

With most metals, the reaction would proceed in the reverse direction (e.g. cleavage of organozinc derivatives by acid, HX). Carbon compounds which react in this way include alkynes, ketones and cyclopentadiene. 

The s-trans complexes, however, react with alkenes, alkynes, ketones and aldehydes by insertion into a M—C bond, leading to metallacycles. 

The alkynyl ketones 840 can be prepared by the reaction of acyi chlorides with terminal alkynes, Cul in the presence of Et3N is the cocatalyst[719]. (1-Alkynyl)tributylstannanes are also used for the alkynyl ketone synthesis[720]. The a,. 3-alkynic dithio and thiono esters 842 can be prepared by the reaction of the corresponding acid chloride 841 with terminal alkynes[721,722]. 

Many aldehydes and ketones are made m the laboratory from alkenes alkynes arenes and alcohols by reactions that you already know about and are summarized m Table 17 1... 

AUylic organoboranes react via cyclic transition states not only with aldehydes and ketones, but also with alkynes, aHenes, and electron-rich or strained alkenes. Bicyclic stmctures, which can be further transformed into boraadamantanes, are obtained from triaHyl- or tricrotylborane and alkynes (323,438,439). 

Sulfitation and Bisulfitation of Unsaturated Hydrocarbons. Sulfites and bisulfites react with compounds such as olefins, epoxides, aldehydes, ketones, alkynes, a2iridines, and episulftdes to give aHphatic sulfonates or hydroxysulfonates. These compounds can be used as intermediates in the synthesis of a variety of organic compounds. 

More definitive evidence for the formation of an oxirene intermediate or transition state was presented recently by Cormier 80TL2021), in an extension of his earlier work on diazo ketones 77TL2231). This approach was based on the realization that, in principle, the oxirene (87) could be generated from the diazo ketones (88) or (89) via the oxocarbenes 90 or 91) or from the alkyne (92 Scheme 91). If the carbenes (90) (from 88) and (91) (from 89) equilibrate through the oxirene (87), and if (87) is also the initial product of epoxidation of (92), then essentially the same mixture of products (hexenones and ketene-derived products) should be formed on decomposition of the diazo ketones and on oxidation of the alkyne this was the case. 

Formation of Alkynes, Alkenes, and Ketones from Boranes and Acetylides... 

Examples of the protection of alkynes, carboxylic acids, alcohols, phenols, aldehydes, amides, amines, esters, ketones, and alkenes are also indexed on p. xvii. Section (designated with an A 15A, 30A, etc.) with protecting group reactions are located at the end of pertinent chapters. 

Despite the great success of the transmetalation process in the enantiose-lective arylation of ketones, its extension to allylation or alkynylation reactions failed, providing the corresponding tertiary alcohols with enantiomeric excesses never higher than 50% ee. On the other hand, more success has been found in the alkenylation of ketones. The process started with the hydrozirconation of terminal alkynes to give the corresponding alkenylzirconium intermediates, which were transmetalated by reaction, in this case, with various ketones in the presence of the HOCSAC ligand. This protocol tolerated the presence of other carbon-carbon multiple bonds on the alkyne, as well as different functionalities and achieved excellent results for alkyl ketones, a,(3-unsaturated ketones and even dialkylketones, as shown in Scheme 4.22. 

The addition of allyl alcohol to alkynes to form y,8-unsaturated ketones and aldehydes (Eq. 3.46) in aqueous media was developed by both Trost and Dixneuf.182... 

---