Cobalt(I)-catalyzed Neutral Diels-Alder Reactions of 1,3-Diynes with Acyclic 1,3-Dienes

Abstract

The cobalt catalyzed neutral Diels-Alder reaction of various acyclic 1,3-dienes and norbornadiene with 1,3-diynes can be controlled to give the 1:1 adduct, whereas the 1:2 adducts are only formed with sterically less hindered 1,3-dienes. With unsymmetrical 1,3-diynes the regiochemistry is mainly controlled by steric factors for unfunctionalized diynes, whereas the regiodirecting methoxymethyl substituent favors the Diels-Alder reaction at the closest triple bond. The combination of steric effects and the methoxymethyl substituent exclusively generates one of the two possible neutral Diels-Alder products. The mild oxidation of the dihydroaromatic products by stoichiometric amounts of DDQ, or alternatively under electrochemical regeneration of the spent oxidizing agent at the anode, generates phenylacetylene derivatives, from the 1:1 adduct, or biphenyl derivatives, from the 1:2 adduct, respectively.

Key words

cobalt - neutral Diels-Alder reaction - 1,3-diyne - 1,3-diene - dihydroaromatic compounds

References

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3

The regioselectivity for the neutral Diels-Alder reactions of 1,3-pentadiene with unsymmetrical alkynes and 1,3-diynes is quite low, generally in the range of 60:40.