The [n]radialenes are a unique family of fundamental [n]-membered carbocyclic structures with radiating alkenes, which have attracted significant synthetic and theoretical attention. Whereas [3]-, [4]-, and [6]radialenes have been prepared and studied, all efforts to synthesize the five-membered ring compound have thus far met with failure. Here we describe the first synthesis of the fundamental hydrocarbon [5]radialene, C10H10. Our approach was a departure from previous radialene syntheses in that it utilized a low-temperature decomplexation of a stable organometallic compound, rather than high-temperature elimination or rearrangement. Our strategy was guided by analysis of previous radialene syntheses, which indicated rapid decomposition in oxygen, and ab initio calculations, which revealed an extraordinary susceptibility of [5]radialene to undergo Diels-Alder dimerization/polymerization. The origin of this susceptibility was traced to a small distortion energy associated with the formation of the transition structure geometry from the relaxed reactant monomers and to a narrow HOMO-LUMO gap.

The first four-fold cross coupling reaction involving alkenic partners leads to the title hydrocarbon on multi-gram scale in one step from commercially available precursors. In stark contrast to its close structural relatives, tetravinylethylene is a remarkably robust, bench-stable compound. The π-bond rich hydrocarbon is shown to undergo one-pot sequences of pericyclic reactions leading to the formation of complex systems with four new rings, seven C-C bonds and ten stereocenters with a very high level of stereoselectivity. Insights into the reactivity of this and related systems is provided using the accurate composite ab initio MO G4(MP2) method.

Computational and experimental studies offer fresh insights into the neglected tetravinylethylene class of compounds. Both the structures and the outcomes of exploratory reactions of the parent hydrocarbon are predicted and explained in detail through high-level composite ab initio MO G4(MP2) computational studies.

The first general synthesis of branched tetraenes ([4]­dendralenes) involves two or three steps from inexpensive, commodity chemicals. It involves an unprecedented variation on Suzuki–Miyaura cross-coupling, generating two new C–C bonds in a one-flask operation with control of diastereoselectivity. The broad scope of the method is established through the synthesis of more than 60 diversely substituted [4]­dendralene molecules, along with substituted buta-1,3-dienes and other [n]­dendralenes. [4]­Dendralenes are demonstrated to be significantly more kinetically stable than their well-known [3]­dendralene counterparts. The first stereoselective synthesis of these compounds is also reported, through the catalyst-controlled generation of both E- and Z-diastereomeric products from the same precursor. Novel, through-conjugated/cross-conjugated hybrid molecules are introduced. The first selective dienophile cycloadditions to substituted [4]­dendralenes are reported, thus paving the way for applications in target-oriented synthesis.

The first four-fold cross coupling reaction involving alkenic partners leads to the title hydrocarbon on multi-gram scale in one step from commercially available precursors. In stark contrast to its close structural relatives, tetravinylethylene is a remarkably robust, bench-stable compound. The p-bond rich hydrocarbon is shown to undergo one-pot sequences of pericyclic reactions leading to the formation of complex systems with four new rings, seven C À C bonds and ten stereocenters with a very high level of stereoselectivity. Insights into the reactivity of this and related systems is provided using the accurate composite ab initio MO G4(MP2) method.Tetravinylethylene (TVE, 1, Scheme 1) is the smallest symmetrical alkene-based structure containing both throughconjugation and cross-conjugation. Very little is known about the structure, stability and reactivity of TVE (1) or its Scheme 1. TVE (1): reported synthesis and related structures.Scheme 2. Four-fold cross-coupling approach to TVE (1).