Aldol reaction, aqueous media intramolecular

Wittig-Homer reaction with 1,4- and 1,5-dialdehydes.1 Reaction of these aldehydes with 1 equiv. of a Wittig-Horner phosphonate in an aqueous medium with K2C03 as base is accompanied by an intramolecular aldolization to provide five- or six-membered cycloalkenols. 

In an intramolecular case, it was shown that, in an aqueous medium, the nature of the acidic or basic catalyst had a dramatic effect on the outcome of the aldolisation (Denmark and Lee, 1992). Acid-induced aldol condensation of ketoaldehyde 1 provided the syn hydroxyketone 2, while the anti isomer 3 arose from base-catalyzed reactions ... 

The aqueous medium influences not only the reaction rate but also the stereoselection of the aldol addition. One significant example [13] is the intramolecular cyclization of ketoaldehyde depicted in Scheme 7.2. In organic solvents there is a preference for syn or anti adduct depending on the presence of coordinating cations (K, Na, Li, MgBr ) or a complexing agent such as... 

A Michael reaction coupled with aldol-type condensation has been used in the one-pot synthesis of allylrethrone (Scheme 7.7), an important component of an insecticidal pyrethroid [32]. The conjugative addition of 5-nitro-l-pentene to methyl vinyl ketone is catalyzed by AI2O3 and occurs in the absence of solvent. An intramolecular aldol-type condensation is then carried out in alkaline aqueous medium after the conversion of the nitro group into a carbonyl by the Nef reaction. 

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See also in sourсe #XX -- [ , ]

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