Tandem Ene/[4 + 2] Cycloaddition Reaction for the Synthesis of 9-Benzylphenanthrenes from Arynes and α-(Bromomethyl)styrenes

A tandem reaction for the synthesis of phenanthrenes from arynes and α-(bromomethyl)styrenes is reported. The transformation proceeds via an ene reaction of α-(bromomethyl)styrenes with arynes, followed by a [4 + 2] cycloaddition reaction. The reaction generates 9-benzylphenanthrene derivatives in moderate to excellent yields.

1,3-Butadiynamides the Ethynylogous Ynamides: Synthesis, Properties and Applications in Heterocyclic Chemistry

1,3-butadiynamides-the ethynylogous variants of ynamides-receive considerable attention as precursors of complex molecular scaffolds for organic and heterocyclic chemistry. The synthetic potential of these C4-building blocks reveals itself in sophisticated transition-metal catalyzed annulation reactions and in metal-free or silver-mediated HDDA (Hexa-dehydro-Diels-Alder) cycloadditions. 1,3-Butadiynamides also gain significance as optoelectronic materials and in less explored views on their unique helical twisted frontier molecular orbitals (Hel-FMOs). The present account summarizes different methodologies for the synthesis of 1,3-butadiynamides followed by the description of their molecular structure and electronic properties. Finally, the surprisingly rich chemistry of 1,3-butadiynamides as versatile C4-building blocks in heterocyclic chemistry is reviewed by compiling their exciting reactivity, specificity and opportunities for organic synthesis. Besides chemical transformations and use in synthesis, a focus is set on the mechanistic understanding of the chemistry of 1,3-butadiynamides-suggesting that 1,3-butadiynamides are not just simple alkynes. These ethynylogous variants of ynamides have their own molecular character and chemical reactivity and reflect a new class of remarkably useful compounds.

The Aryne Ene Reaction

Intermolecular aryne ene reactions present opportunities to arylate a wide range of unsaturated substrates in a single step, whilst intramolecular reactions provide expedient access to valuable benzofused carbo- and heterocyclic frameworks. This short review will chart the development of the aryne ene reaction from initial reports that rationalise unexpected byproduct formation in competing [4+2] and [2+2] cycloadditions through to its exploitation in contemporary synthetic methodology.

1 Introduction

2 Alkene Ene Reactions

2.1 Intermolecular

2.2 Intramolecular

3 Alkyne Ene Reactions

3.1 Intermolecular

3.2 Intramolecular

4 Allene Ene Reactions

5 Aromatic Ene Reactions

6 Hetero Ene Reactions

6.1 Enols

6.2 Enamines

6.3 Imines

7 Conclusions

A Rare Alder-ene Cycloisomerisation of 1,6-Allenynes

Thermally induced cycloisomerization reactions of 1,6-allenynes gives α-methylene-γ-lactams via intramolecular Alder-ene reactions. The mechanism is supported by computational and deuterium labeling studies. This thermal, non-radical method enables the discovery of a hitherto unknown route that proceeds via a divergent mechanism distinct from the previous [2+2] cycloisomerization manifold.