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An aqueous medium containing catalytic amounts of a tertiary amine was employed to direct the chemoselectivity of the reaction of aldehydes with 1a. With DBU, 2 was formed at room temperature as a rare exemplary of Baylis-Hillman reactions in heterocyclic enones. DABCO alternated the pathway toward an aldol reaction to form syn/anti mixtures of 3 with the syn isomers being the major products. With Et(3)N, aldol condensation dominated., (© 2011 American Chemical Society)

A room temperature convenient disproportionation or reduction of aldehydes prompted by lithium bromide and triethylamine is described in a solvent-free environment. Distribution of the products to selectively direct the process toward Cannizzaro or Tishchenko reactions is controlled by the type of workup selection. The presence of hydrogen donor alcohols in the mixture completely diverts the process toward the Meerwein-Ponndorf-Verley reaction.

[reaction: see text] A room-temperature convenient Cannizzaro reaction prompted by magnesium bromide ethyl etherate and triethylamine is described for smooth conversion of aromatic aldehydes into their respective alcohols and carboxylic acids. The methodology is applicable to both inter- and intramolecular reactions and could be directed to obtain the carboxylic moiety in the form of an acid, an amide, or an ester compound depending on the selected reaction conditions or workup procedure.

Diels-Alder reactions of 2,4-hexadienol or its O-methyl ether with acrylate derivatives at 120 degrees C give mixtures of the four possible adducts with low selectivity. At ambient temperature and in the presence of Mg(II) or Al(III) Lewis acids, reactions of the dienol (but not the ether) are highly selective. Control experiments suggest that the Lewis acid serves both to tether the diene and dienophile and to induce an "intramolecular" reaction of the resulting "self-assembled" intermediate.