Search

Abstract: An efficient access to tetrahydrofuran‐fused bicyclo[2.2.2]oct‐2‐enes via palladium‐catalyzed cyclization of oxygen‐tethered 2,7‐alkadiynylic carbonates with 2‐(buta‐2,3‐dienyl)malononitrile has been developed. Perfect chiral induction was observed when a substituent was introduced to the propargylic position affording the optically active polycyclic products of both enantiomers. Control experiments showed that the oxygen tether of 2,7‐alkadiynylic carbonates and the two cyano groups in allene are indispensible for this transformation. [ABSTRACT FROM AUTHOR]

Allene-yne-allene and allene-ene-allene N-tosyl-linked substrates with two chiral centres in the α-position of the allene moiety were satisfactorily prepared starting both from racemic and chiral propargylic alcohols. The Wilkinson's complex-catalyzed [2+2+2] cycloaddition reaction of these substrates was evaluated. In the case of enantiomerically pure bisallenes, high stereoselectivity was observed, giving a diastereomerically pure cycloadduct. The chirality of starting bisallene substrates can be completely transferred to the cycloadducts, representing an atom-economical and enantiospecific process for the construction of fused polycycles. However, when reacting an oxygen-linked allene-ene-allene substrate, the stereoselectivity decreased and two diastereoisomers were formed. A detailed characterization study of the resulting cycloadducts allowed us to identify the enantioisomer generated in the cycloaddition. [ABSTRACT FROM AUTHOR]