Allyhc hahdes

It is possible to combine both the type I and the type II situations in the coupling of a chiral aldehyde with a substituted allyhc hahde. Such is the case in the coupling of unprotected aldoses (e.g., glyceraldehyde)... 

Substituted allyhc hahdes give mixtures of products resulting from bond formation at both C-1 and C-3 of the allyhc system, with the product ratio favoring the product formed by reaction at the less substituted site. The portion of the product formed by reaction at C-1 in allyhc systems may result from direct substitution, but it has also been suggested that a... 

N-Alkylpyrroles may be obtained by the Knorr synthesis or by the reaction of the pyrrolyl metallates, ie, Na, K, and Tl, with alkyl haUdes such as iodomethane, eg, 1-methylpyrrole [96-54-8]. Alkylation of pyrroles at the other ring positions can be carried out under mild conditions with allyhc or hensylic hahdes or under more stringent conditions (100—150°C) with CH I. However, unless most of the other ring positions are blocked, poly alkylation and polymerisation tend to occur. N-Alkylation of pyrroles is favored by polar solvents and weakly coordinating cations (Na", K" ). More strongly coordinating cations (Li", Mg " ) lead to more C-alkylation. 

The Heck reaction may also proceed in an intramolecular fashion if the aryl hahde is covalently boimd to the aUyl substrate. In this case the sequential allyhc substitution-Heck-cycIization with Pd acetate as a catalyst takes place very smoothly as an imimolecular process and furnishes the polycon-densed pyrroHdones 91 in excellent yields (Scheme 29). 

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