Several phthalocyanines carrying hydrophobic components have been synthesized and shown to bind to a group of cyclodextrin dimers with a carbon−carbon double bond in the linker. The complexes are soluble in water. On irradiation in the presence of oxygen, the singlet oxygen produced cleaves the olefinic linkers in the complexes, resulting in precipitation of the sensitizers. This process concentrates the sensitizers in the light beam, a process that has useful potential in photodynamic therapy.

Cyclodextrin dimers as cleavable carriers of photodynamic sensitizers.

The addition of stabilized nucleophiles to activated π-systems is one of the oldest and most useful constructive methods in organic synthesis, dating back more than a hundred years. In 1887 Michael, after whom the most well-known example of this reaction was named, published the first of a series of papers on this reaction describing the addition of the sodium salt of both diethyl malonate (1) and ethyl acetoacetate (2) to ethyl cinnamate (3) to give the products (4) and (5), respectively (equation 1).1 This Michael reaction, in which a carbanion stabilized by one or usually two electron-withdrawing groups adds to the β-carbon of an α,β-unsaturated carbonyl derivative, represents one of the earliest and most highly utilized methods for carbon–carbon bond formation. In that same 1887 paper,1a Michael also reported the synthesis of triethyl cyclopropane-1,1,2-tricarboxylate (9) from (1) and ethyl α-bromoacrylate (6) via the intermediates (7) and (8), a synthetic route to cyclopropanes used often today (Scheme 1). In 1894 he showed that an alkynic ester could also function as the electrophilic component in these reactions, e.g. (1) and (10a) or (10b) giving (11a) or (11b), respectively (equation 2).2 This reaction and its variants were in wide use around the turn of the century to prepare straight chain polycarboxylates, e.g. the reaction of (12) to give (13; equation 3) and cyclohexane-1,3-diones, e.g. (15; equation 4) (via Knoevenagel and Claisen condensations).3 The combination of Michael addition followed by intramolecular aldol condensation and decarboalkoxylation furnishes cyclohexenones, e.g. isophorone (17; equation 5), from enones such as mesityl oxide (16) and the salt of ethyl acetoacetate (2).4 This process of annulation was made much more general in the 1930s by Robinson and his coworkers,5 who showed that vinyl ketones and their derivatives, e.g. Mannich bases, could be used with simple ketone enolates to produce cyclohexenones of a wide variety, e.g. (20; equation 6), a process which has come to be known as the Robinson annulation.6

Stabilized Nucleophiles with Electron Deficient Alkenes and Alkynes

Highly selective palladium-catalyzed internal alpha-arylations of alkyl vinyl ethers with aryl and heteroaryl bromides were conveniently conducted in aqueous DMF with potassium carbonate as base and with DPPP as bidentate ligand. The corresponding acetyl arene products were, after hydrolysis, isolated in good to excellent yields. This Heck reaction procedure does not require toxic thallium or expensive silver salt additives, is promoted by water, and is suggested to proceed via charged organopalladium intermediates. Single-mode microwave irradiation was utilized in one example to shorten the reaction time.

Aqueous DMF−Potassium Carbonate as a Substitute for Thallium and Silver Additives in the Palladium-Catalyzed Conversion of Aryl Bromides to Acetyl Arenes

Celmira da G. Burgos

Papers

Annulation of α-formyl α,β-unsaturated ketones by a Michael addition-cyclization sequence. A versatile synthesis of alicyclic six-membered rings