Synthesis and new reactions of allenyl carbonyls

We report here the development of new and more general synthetic pathways for the preparation of allenyl and alkynyl carbonyls. These highly dense functionalized compounds were utilized as key intermediates for the synthesis of [3.2.1] and [3.3.1] bicyclic framework, the motifs found in many natural products. A convenient method described for the dehydration of ketoesters to generate conjugated and deconjugated alkynyl esters and conjugated allenyl esters. This sequential one-pot method involves the formation of a vinyl triflate monoanion intermediate that leads to the selective formation of alkynes or allenes depending on additives and conditions used. Product outcomes appear to be a function of unique monoand dianion mechanisms which are described. Our design of a Morita-Baylis-Hilman (MBH) reaction to include a fast silyl 1,3- Brook rearrangement has enabled the first ever anion-catalysis. This new reaction makes possible the addition of both aliphatic and aromatic aldehydes to s ilylallenes leading to carbinol allenoates. These new MBH reactions products allow for a fasttracked synthesis of [3.2.1] bisoxa-bicycles which make up the framework of many biologically active natural products including Vitisinol D. The development of cyclic addition of hydrazine nitrogen to unactivated alkynes catalyzed by non-metals is reported. Starting from readily accessible silyl allenyl esters, alkynyl hydrazines are prepared in one step and subsequently undergo unprecedented cyclization reactions in the presence of ammonium and phosphonium catalysts leading to dehydro-azaproline products. These heterocycles were also produced in high enantiomeric excesses using chiral ammonium phase transfer catalysts via a kinetic resolution pathway.