Hydrogenation acyclic

Reductions of aromatic carbonyl compounds a-substituted carbonyl compounds a-hydroxy ketones p- and y-substituted carbonyl compounds ketones and a- and p-diketones P-keto acids and esters, y-kcto esters masked carbonyl compounds activated double bonds (hydrogenation) acyclic and cyclic ketones reductive amination of keto acids BY BY BY, glycerolDH BY BY, An, Cr, Cu, Gc, Ha, Ks, Mi, Mr, Ns, Pd, Pm, Rn, Y1 BY, Ao, Cb, Cg, Cu, Ct, Gc, Hp, Lk, Mj, Pf, Pm, Pv, Rr, Td, glycerolDH BY BY, An, Gc, Pc HLADH, TBADH, other ADHs, HSDHs AADH, GluDH, PheDH... 

The Wiener index was originally defined only for acyclic graphs and was initially called the path number [6]. "The path number, W, is defined as the sum of the distances between any two carbon atoms in the molecule in terms of carbon-carbon bonds". Hosoya extended the Wiener index and defined it as the half-sum of the off diagonal elements of a distance matrix D in the hydrogen-depleted molecular graph of Eq, (15), where dij is an element of the distance matrix D and gives the shortest path between atoms i and j. 

Since Our target molecule is acyclic and monofunctional the obvious solutions to our problem are stereoselective alkylations and hydrogenations (see scheme above), e.g. ... 

Stereochemical features in the oxidative addition and the elimination of /3-hydrogen of cyclic and acyclic alkenes are different. The insertion (palladation) is syn addition. The syn addition (carbopalladation) of R—Pd—X to an acyclic alkene is followed by the syn elimination of 3-hydrogen to give the trans-a ksne 6, because free rotation of 5 is possible with the acyclic alkene. On the other hand, no rotation of the intermediate 7 is possible with a cyclic alkene and the syn elimination of /3-hydrogen gives the allylic compound 8 rather than a substituted alkene. 

By condensing the salts or the esters of either dithioformic (207) or dithiophenacetic acids with a-aminonitriles (206) 5-aminothiazoles (209), in which R] = hydrogen, benzyl and Rj = phenyl, carbethoxy, or car-bophenoxy, were obtained in fairly good yields (Scheme 108) (271). These reactions were carried out in aqueous ethereal solution at room temperature. Acyclic thioamides as intermediates in this reaction have been isolated in some cases (208). 

In some cases, the acyclic intermediates (229) of 230, R] = aryl, R2 = hydrogen, were isolated (424), They undergo cyclization to thiazoles upon heating in toluene. Some 2-aryl-4-hydroxythiazoles prepared by this procedure are listed in Table 11-39. 

Alkylisothiazolium salts (61) undergo N—S bond cleavage when treated with hydrogen sulfide or thiophenol to form acyclic products (62), but 2-aryl compounds give 1,2-dithioles (63 or 64 Scheme 9) (75SST(3)54l, 77SST(4)339). 

The stereochemistry of radical addition of hydrogen bromide to alkenes has been studied with both acyclic and cyclic alkenes. Anti addition is favored.This is contrary to what would be expected if the s[p- carbon of the radical were rapidly rotating or inverting with respect to the remainder of the molecule ... 

Intramolecular hydrogen-atom abstraction is also an important process for acyclic a,/ -unsaturated ketones. The intermediate diradical then cyclizes to give the enol of a cyclobutyl ketone. Among the by-products of such photolyses are cyclobutanols resulting from alternative modes of cyclization of the diradical intermediate ... 

The mechanism of the Cook-Heilbron reaction between a-aminonitriles and dithioformic ester 6 proceeds via an acyclic intermediate 7, as proven by its isolation in several cases. Nucleophilic attack of the amine function on the sulfur-bearing carbon leads to the elimination of hydrogen sulphide. Cyclization of the acyclic thiacetoamide results in a five membered ring which aromatises favourably to give 5-amino-2-benzylthiazole 8. 

Shaw and McDowellhave prepared imidazolone derivatives by cyclization of a-acylamino amides. In a variation of this reaction the azlactone (30) was gradually converted to the hydroxamic acid (31) by methanolic hydroxylamine. Sodium methoxide and hydroxylamine readily gave the acyclic hydroxamic acid (32) which could be cyclized to 31 by dilute acid. Benzyloxyurea has been used in the sjrnthesis of pyrimidine hydroxamic acids (33) by reaction with /S-diketones followed by catalytic hydrogenation of the benzyl group. Protection... 

The thermolysis of xanthates derived from primary alcohols yields one olefin only. With xanthates from secondary alcohols (acyclic or alicyclic) regioisomeric products as well as fi/Z-isomers may be obtained see below. While acyclic substrates may give rise to a mixture of olefins, the formation of products from alicyclic substrates often is determined by the stereochemical requirements the /3-hydrogen and the xanthate moiety must be syn to each other in order to eliminate via a cyclic transition state. 

Both terminal and internal acyclic alkenes can be metathesized, corresponding to Eq. (4), where R is an alkyl group or a hydrogen atom. 

To summarize under favorable conditions the acidity of a-hydrogens facilitates the generation of a-sulfoxy and a-sulfonyl carbanions in thiirane and thiirene oxides and dioxides as in acyclic sulfoxides and sulfones. However, the particular structural constraints of three-membered ring systems may lead not only to different chemical consequences following the formation of the carbanions, but may also provide alternative pathways not available in the case of the acyclic counterparts for hydrogen abstraction in the reaction of bases. 

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