Introduction conjugation

Tlie latter reagent undergoes 1,2-addition to a,p-unsaturated aldehydes 1,4-addition, with copper catalysis, is observed with cyclohexenone alone. A more satisfactory reagent for the conjugate introduction of the hydroxymethyl group is the allyldimethylsilylmethyl Grignt reagent... 

The UV spectrum of a complex conjugated molecule is usually observed to consist of a few broad band systems, often with fine structure, which may be sharpened up in non-polar solvents. Such a spectrum can often be shown to be more complex than it superficially appears, by investigation of the magnetic circular dichroism (MCD) spectrum, or by introduction of dissymmetry and running the optical rotatory dispersion (ORD) or circular dichroism (CD) spectrum. These techniques will frequently separate and distinguish overlapping bands of different symmetry properties <71PMH(3)397). 

Gutman and S. J. Cyvin, Introduction to the Theory of Benzenoid Hydrocarbons, Springer-Verlag, Berlin, 1989. 3 Lloyd, Nonbenzenoid Conjugated Carbocyclic Compounds, Elsevier, Amsterdam, 1984. 

Enolizalion of conjugated or /3,y-unsatiirated enones and dienones in O-deiiterated solvents facilitates the introduction of deuterium labels into positions as far as three and five carbon atoms away from a given ketone function. Exchange of the activated hydrogens in androst-4-en-3-one (12) provides a good illustration of the potential of this method. Saturation of the double bond (section V) in the deuterated enone (13) followed by back exchange of the a-deuteriums (section II-B) proves to be an excellent method for the preparation of 6,6-d2-5a-androstan-3-one (15). ... 

These are usually obtained from the isomeric conjugated ketone, and are sometimes useful as intermediates, offering an alternative to enol derivatives. They may also be formed as a result of double bond introduction or by oxidation of homoallylic alcohols if so the conditions must be mild because they generally represent a less stable isomer. 

Both conjugated and isolated dienes are usually accessible by extension of the methods suitable for mono-olefins. Allylic functions for ehmination may be produced by double bond introduction a to a functional group or by allylic substitution of an olefin. Both reduction of allylic systems to mono-olefins and elimination to give dienes, may involve rearrangement. 

The stereochemistry of the 1,4-addition to A -octal-l-one and 1,1-di-methyl-A -octal-2-one has been investigated by House and Marshall, respectively. In summary, steric and stereoelectronic factors play a part in the mechanism of conjugate addition of Grignard compounds. With methylmagnesium iodide, the introduction of an axial methyl group into steroidal 5a-A -3-ketones (3) and 5 -A -3-ketones (6) is favored by stereo-electronic factors in the transition state. 

The introduction of a double bond in conjugation with the nitrogen atom fcsults in a bathochromic shift. For instance, in contrast with the saturated amines (A ,, —215 mp, e — 3000), the enamines show a maximum at... 

Hydrogen was recognized as the essential element in acids by H. Davy after his work on the hydrohalic acids, and theories of acids and bases have played an important role ever since. The electrolytic dissociation theory of S. A. Arrhenius and W. Ostwald in the 1880s, the introduction of the pH scale for hydrogen-ion concentrations by S. P. L. Sprensen in 1909, the theory of acid-base titrations and indicators, and J. N. Brdnsted s fruitful concept of acids and conjugate bases as proton donors and acceptors (1923) are other land marks (see p. 48). The di.scovery of ortho- and para-hydrogen in 1924, closely followed by the discovery of heavy hydrogen (deuterium) and... 

The stereoselective introduction of two methyl groups into / -(- -)-5-hydroxy-methyl-2(5// )-furanone 143 was effected by tritylation followed by the conjugated addition (87JOC1170) of McaCuLi (TMSCl/EtaO, -78°C) and, finally, treatment with LiN(TMS)2/MeI (Scheme 43) (97TL1439). 

Introduction of an additional methyl group on the donor atom of TMM moiety gives a low 33% yield of the perhydroindans (49, X=H2) and (50, X=H2) with substantial production of the diene by-products [24]. However, it is still remarkable that the reaction works at all since the corresponding intermolecular cycloaddition failed. Incorporation of a carbonyl moiety adjacent to the donor carbon atom doubles the yield of the cycloadducts to 66% (Scheme 2.15). This so-called acyl effect works by making the donor carbon of the TMM unit "softer," thus facilitating the initial step of the conjugate addition, as well as inhibiting base-induced side reactions [22]. 

Deletion of the 17a-hydroxy group similarly leads to an effective topical antiinflammatory agent. Treatment of 16a-methylpregnenolone (244) (obtained by conjugate addition of an organometallic to pregnenolone) sequentially with bromine and acetate ion affords the 21 acetate, 245 (see, for example, the transformation of 196 to 198). In an interesting variation on the method for the introduction of a fluorine atom at 6, the... 

Step 1 of Figure 29.3 Introduction of a Double Bond The /3-oxidation pathway begins when a fait)7 acid forms a thioester with coenzyme A to give a fatty acyl Co A. Two hydrogen atoms are then removed from C2 and C3 of the fatty acyl CoA by one of a family of acyl-CoA dehydrogenases to yield an a,/3-unsaturated acyl CoA. This kind of oxidation—the introduction of a conjugated double bond into a carbonyl compound—occurs frequently jn biochemical pathways and usually involves the coenzyme flavin adenine dinucleotide (FAD). Reduced FADH2 is the by-product. 

Aromaticity (Chapter 15 introduction) The special characteristics of cyclic conjugated molecules. These characteristics include unusual stability, the presence of a ring current in the 1H NMR spectrum, and a tendency to undergo substitution reactions rather than addition reactions on treatment with electrophiles. Aromatic molecules are planar, cyclic, conjugated species that have An + 2 7T electrons. 

Conjugation (Chapter 14 introduction) A series of overlapping p orbitals, usually in alternating single and multiple bonds. For example, 1,3-butadiene is a conjugated diene, 3-buten-2-one is a conjugated enone, and benzene is a cyclic conjugated triene. 

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