[Show abstract][Hide abstract] ABSTRACT: [reaction: see text] A total synthesis of (+)-aspidospermidine (1) is described. The key reactions used in the synthesis of this pentacyclic Aspidosperma alkaloid were a deracemizing imine alkylation/Robinson annulation sequence, a selective "redox ketalization", and an intramolecular Schmidt reaction. A Fischer indolization step carried out on a tricyclic ketone mirrored the sequence reported by Stork and Dolfini in their classic aspidospermine synthesis.
The Journal of Organic Chemistry 01/2006; 70(26):10645-52. · 4.56 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The Lewis acid-promoted reactions of alkyl azides with ketones can afford several products. Chief among these result from a Schmidt-like insertion of the azide into the carbon−carbon bond adjacent to the carbonyl group. Alternatively, an acid-promoted rearrangement of the azide to an iminium species can occur, mostly with benzylic azides; the iminium species can then be trapped by the enol of the carbonyl compound in a variation of the Mannich reaction. The scope of each of these reactions, the dependence of the observed products upon azide and ketone structure, and the nature of acid promotion are discussed. In broad strokes, cyclohexanones and other cyclic ketones react in the presence of TiCl4 to afford insertion products, whereas the Mannich route predominates when benzyl azide and triflic acid are used. The features that lead to each reaction type and possible mechanistic implications are discussed.
Journal of The American Chemical Society - J AM CHEM SOC. 07/2000; 122(30).
[Show abstract][Hide abstract] ABSTRACT: [reaction--see text] A total synthesis of (+)-aspidospermidine (1) is described, featuring an intramolecular Schmidt reaction as the key step. The effects of stereochemistry and protecting group status on the regio- and chemoselectivity of this reaction were examined.
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[Show abstract][Hide abstract] ABSTRACT: Treatment of benzyl azide with triflic acid or titanium tetrachloride effects 1,2-phenyl migration with concomitant liberation of molecular nitrogen. The resulting N-phenyl iminium ion intermediate readily combines with enolizable carbonyl substrates to form Mannich bases.