Ketones, conjugated, reaction with

The self-condensation is largely suppressed in reactions with those ketones 2, that are activated by an electron-withdrawing substituent or R". The carbonyl activity is then increased, and the enamine-intermediate 5 is favored over the imine 4, by conjugation with the electron-withdrawing group. ... 

The titanium reagent also dimethylates aromatic aldehydes." Triethylaluminum reacts with aldehydes, however, to give the mono-ethyl alcohol, and in the presence of a chiral additive the reaction proceeds with good asymmetric induction." A complex of Me3Ti-MeLi has been shown to be selective for 1,2 addition with conjugated ketones, in the presence of nonconjugated ketones." ... 

As with other reactions, silyl esters of phosphorus acids constitute an important and useful category of reagents for conjugate addition reactions. With aldehydes, ketones, and esters, the silyl ester linkage is transferred to the carbonyl oxygen, facilitating the completion of the reaction, generating the free carbonyl or ester upon workup with a protic solvent (Equation 3.25). 

Scheme 9.14 Proposed pathway for the reaction of allenylsilanes with conjugated ketones leading to acylcyclopentenes.

The reaction of alkenes with iodosobenzene in acetic acid in the presence of sodium azide offers a simple and high yield route to 1,2-diazides (Table 3)76. a-Azido ketones are side products or the exclusive product from the reaction with conjugated alkenes. Allylic azides or oxonitriles, resulting from oxidative cleavage of the C-C double bond, are alternatively obtained from trisubstituted steroid alkenes77. 

Recently, Shchepin and coworkers described Michael addition reactions with zinc ketone enolates (144) for the preparation of chroman-2-one derivatives 146. The enolates were generated in situ from a-bromo ketones 143 by addition of excess zinc (equation 40), and subsequent conjugate addition to a, S-unsaturated ketones (145) (equation 40 ) provided chroman-2-ones (146a, b) in yields up to 82% . 

Conjugate addition (Michael addition) occurs when enamines react with conjugated ketones. This reaction is discussed in Section 15-24. 

A variant of this reaction couples halides with alkenes. ot-Bromomethyl esters react with conjugated ketones and DABCO to give a coupling product, 34. ° A similar DBU-induced reaction was reported using ot-bromomethyl esters and conjugated nitro compounds. 

Compound A is clearly the enamine from the aldehyde and piperidine and its reaction with unsaturated ketone would be expected to lead to conjugate addition (Chapter 29). Evidently, in [Pg.402]

In contrast with conjugated ketones and esters, the reaction between conjugated amides and all types of RMgX proceeds through a 1,4-addition [1-4], particularly with the allylic [21,22] and allenylic [6] organomagnesium derivatives [Eq. (7)] ... 

The reactions of lithiated tris(phenylthio)-, methoxyphenylthiotrimethylsilyl-, bis(methylthio)tri-methylsilyl- and bis(methylthio)stannylmethanes with conjugated ketones give the corresponding 1,4-adducts exclusively. 

Results of infrared spectroscopy studies have confirmed that COOH groups, or more precisely carboxylate (COO—), play a prominent role in the complexing of metal ions by humic and fulvic acids. Some evidence indicates that OH, C=0, and NH groups may also be involved (Vinkler et al., 1976 Boyd et al., 1979 Piccolo and Stevenson, 1981). The suggestion has been made (Piccolo and Stevenson, 1981) that, in addition to the above, complexes may be formed with conjugated ketonic structures, according to the following reactions ... 

Secondary amines used for reactions with cyclic ketones may be aziridine (52X azetidine (53), pyrrolidine (54), piperidine (55), hexamethylenimine (56), morpholine (57), //-methylpiperazinc (58) and acyclic amines like dimethyla-mine (59). The general order of electrophilic attack of enamines as dependent on the nature of the amine moiety decreases in the sequence pyrrolidine (54) > dimethylamine (59) > hexamethylenimine (56) > piperidine (55) sk azetidine (53) > morpholine (57). This sequence seems to parallel the magnitude of conjugative interaction between the amino group and the C=C double bond as indicated by the H NMR chemical shift of the hydrogen at the jS-carbon. 

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