Abstract
The palladium-catalyzed coupling of unsaturated halides or triflates with organostannanes (the Stille reaction) or with organo-boronic acids (the Suzuki reaction) has envolved as a powerful means of carbon-carbon bond formation. As an extention of our work on the synthesis and reactivity of positively charged bridge-head nitrogen containing fused azinium salts, we have been studying the formation of polyfused heteroaromatics with angular anellation pattern.The reaction of such positively charged salts with nucleophiles has proven to be a suitable tool for the preparation of heteroaryl dienes, which have been shown to be excellent intermediates for several ring closure reaction. A selection of results will be presented, including applications to natural product synthesis.
Highlights
In organic chemistry the formation of carbon-carbon bonds - especially between sp2-atoms - has always been a great challenge
In the last decades the introduction of organometallic reagents and catalysts into organic synthesis opened up new routes to establish such connections
Our aim was the synthesis of various pyridine, pyridazine- and v-triazine-containing angularly fused heteroaromatic systems implaying the strategy shown in Scheme 1, which is based on the ring-closure of the suitably substituted asymmetric biaryl compounds prepared from the corresponding organometallics and aryl halides by Pd(0)-catalysed cross-coupling reaction
Summary
In organic chemistry the formation of carbon-carbon bonds - especially between sp2-atoms - has always been a great challenge. Our aim was the synthesis of various pyridine-, pyridazine- and v-triazine-containing angularly fused heteroaromatic systems implaying the strategy shown in Scheme 1, which is based on the ring-closure of the suitably substituted asymmetric biaryl compounds prepared from the corresponding organometallics and aryl halides by Pd(0)-catalysed cross-coupling reaction. Somewhat to our surprise we isolated the corresponding N-oxide derivative (7) of the expected ring-closed product in 76% yield.
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