Hexadehydro Diels-Alder/Alkynyliodanation Cascade: A Highly Regioselective Entry to Polycyclic Aromatics

Abstract

We report here a cascade process integrating the hexadehydro Diels-Alder (HDDA) reaction with alkynyliodanation, enabling efficient synthesis of highly substituted aryl-λ³-iodanes. Heating a mixture of a tetrayne and an alkynylbenziodoxole induces regioselective insertion of the tetrayne-derived aryne into the alkynyl-iodine(III) bond, yielding a 1,4-dialkynyl-2-iodanyl-3-aryl(or alkyl)benzene derivative. The unique regiochemistry facilitates subsequent π-extension, allowing divergent access to polyaromatic frameworks, such as helicenes and cyclopenta[cd]pyrenes, underscoring the utility of aryne carboiodanation in complex aromatic synthesis.

Scheme 1. HDDA–Aryne Trapping Reactions for the Synthesis of Polycyclic Aromatic Hydrocarbons

Scheme 2. HDDA/Alkynyliodanation Cascade: Scope of EBXs and Tetraynes

The reaction was performed using 0.1 mmol of 1 and 0.2 mmol (2 equiv) of 2. The regioisomer ratio (determined by ¹H NMR) is shown in the parentheses.

Figure 1

DFT-optimized structures of aryne generated via HDDA of 1h (INT) and transition states of alkynyliodanation with Ph-BEX (2a) leading to 3ha (TS1) and its regioisomer (TS2) (level: M06-2X/6-311++G(2df,2p)-SDD (for I)/SMD(MeCN)//M06-2X/6-31G(d)-SDD (for I)). The distances are shown in Å.

Scheme 3. π-Extension of Polysubstituted Aryl-BXs for the Synthesis of Polycyclic Aromatic Compounds

See the Supporting Information for the detailed reaction conditions.