Addition Acceptors

Fluorme-containing Michael addition acceptors have been used as synthons, a portion of a molecule recognizably related to a simpler molecule, for the introduction of fluorine into the organic molecules Their reactions with enamines and ketones lead to a condensarion-cyclization process... 

The trifluorinated a, J-ethylenic ketone shown in equation 36 was prepared by two different methods and behaves like a Michael addition acceptor in reactions... 

Figure 14.21 Michael addition acceptors (i) carbonyl, (ii) sulfonyl, and (iii) phosphoryl group.

Table 14.15 Critical structural features which can affect the carcinogenicity of Michael addition acceptors.

Reduce the cross-linking potential by avoiding bi- or polyfunctional Michael addition acceptors. 

The use of heteroaryl vinyl sulfides and vinyl dithiocarbamates (166) as hetero-Michael addition acceptors has been described. Combined chelating and electron-withdrawing effects were postulated to stabilize the transient anionic species and allow smooth Michael-induced ring closure to produce C-glycosides (167).191... 

If in addition acceptors are present in great excess, then both the accumulation and recombination of the geminate ion pairs can be considered, using instead of the particle densities the survival probabilities of the excited state, R(t) = N (t) /N (0), and ions, R- = A /N (0). In particular, they obey the original UT equations that follow from the general set (3.418) at kR = 0 and A = c... 

Introduction of additional acceptor thienyl substituents at the silicon in siloxygerma-tranes 207 increases the SiOGe angle (133.0° for 207a, 134.8° for 207b, 139.6° for 207c and 180° for 207d)589. 

The trifluorinated a./ -unsaturatcd ketone 43 can be prepared by two different methods and behaves like a Michael addition acceptor in reaction with nucleophilic species.1 Is reaction with an enamine gives an annulation product 44. This sequence constitutes a method to build up a ring bearing a trifluoromethyl group. 

It has been shown that benzils (323) react with Michael addition acceptors (324) in the presence of a catalytic amount of cyanide ion to yield 1,4-diketones (325). The authors proposed that (325) are produced through the formation of the O-aroylmandelonitrile anion, followed by Michael addition and rearrangement of the aroyl group with decyanation (see Scheme 77). The mechanism of the base-catalysed ring fission of 2,2-dihydroxyindane-l,3-diones has been investigated and the pathway set out in Scheme 78 has been proposed for the transformation. The base-catalysed ring... 

An impressive alternate approach to the synthesis of furans beginning with alkynols was developed by Balme [160, 161] and subsequently applied in a total synthesis by Morimoto [162]. Balme discovered that a three-component coupling reaction between a propargylic alkoxide, a conjugate addition acceptor, and an unsaturated halide yields a variety of di- and trisubstituted furans. In one example, propargyl alcohol, diethyl ethoxymethylene malonate (193), and iodobenzene combine to furnish disubstituted furan 194 in... 

Another category of reactive enones is 4-deoxy-l,2-0-isopropylidene-L-glycero-pent-4-enopyrano-3-ulose, originally synthesized by Klemer and Jung (25) and currently explored by us as an extremely useful new chiral building block for stereoselective functionalization reactions, especially as Michael addition acceptors (Scheme 6). 

The substitution of halogens in position 4 of the isoxazole ring is so disadvantageous that it does not take place even if an additional acceptor is present in position 5. The spiro-product 163 was only obtained after long refluxing in THF (85JCS(P1)1871) (Scheme 72). 

---