Addition to Vinyl Sulfones

Alternatively, the enamine portion may be located in the Aralkyl chain. For instance, piperidines bearing a 7-chloro substituent yielded quinolizidines 263 through a conjugate addition of the nitrogen atom to acetylenic sulfones followed by an intramolecular alkylation (Scheme 55) <2000JOC4543>. Other cyclizations that are summarized below used as starting materials piperidine derivatives obtained by similar conjugate additions to vinyl sulfones (see Section 12.01.9.3.6). 

Table 6.12 Cinchona-derivative-catalyzed conjugate additions to vinyl sulfones.

Cinchona-Derivative-Catalyzed Conjugate Additions to Vinyl Sulfones [38] (p. 206)... 

A similar reaction has been adopted for the preparation of amides from alkenes by the photoaddition of "CONH2 radicals generated from formamide by benzophe-none [7], or via a TBADT [25] photocatalyzed hydrogen abstraction. Solar light has been used in the first case. Furthermore, the introduction of an ester function has been accomplished by generating an alkoxycarbonyl radical by photolysis of [bis(alkoxyoxalyloxy)iodo]benzene at 0-5 °C and ensuing addition to vinyl sulfones in the presence of 1,4-cyclohexadiene [9]. 

Acceptor-substituted alkenes that are employed as substrates in Michael additions include a./l-unsaturated ketones (for example, see Figure 10.59), a,/3-unsaturated esters (Figure 10.60), and a,/3-unsaturatcd nitriles (Figure 10.61). The corresponding reaction products are bifunctional compounds with C=0 and/or C=N bonds in positions 1 and 5. Analogous reaction conditions allow Michael additions to vinyl sulfones or nitroalkenes. These reactions lead to sulfones and nitro compounds that carry a C=0 and/or a O N bond at the C4 carbon. 

For example, the addition to vinyl sulfones has attracted a lot of attention mainly because of the synthetic possibilities that the sulfone group affords in terms of its wide possibilities to undergo a wide variety of transformations. iPBP 15a and prolinal-deiived aminal 12b catalysts have proved their usefulness in the Michael addition of aldehydes to this particular class of Michael acceptors, showing that good yields of the desired Michael adducts could be obtained under the optimized conditions, although with moderate enantios-electivities (Scheme One of the main problems of this particular... 

Scheme 2.99 Catalytic enantioselective conjugate addition to vinyl sulfones...

In order to explain the stereoselectivity of this reaction, the authors have proposed a plausible transition-state model depicted in Scheme 1.5, in which the bulky biaryl silyl ether moiety exerted steric shielding, resulting in the formation of the observed stereoisomer. This enantioselective addition to vinyl sulfones, in combination with desulfonation, offered a unique, asymmetric entry to a-alkylated aldehydes and their derivatives. 

Reactions WITH EtECTROPHitic AtKENEs 2.1.3.1 Nucleophilic Addition to Vinyl Sulfones... 

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