A new one-pot approach to construct α-carbonyl bicyclic furans from easily accessible diynones is described. This reaction sequence proceeds via a Diels-Alder cycloaddition reaction catalyzed by dimethylaluminum chloride followed by a 5-exo-dig cyclization/oxidation reaction catalyzed by copper(II) chloride. This methodology generates α-carbonyl-functionalized dihydroisobenzofuran derivatives in good to excellent yields.

General Methods. All reactions were performed in flame-dried glassware under a N 2 atmosphere. Solvents were degassed and dried by standard methods before use. Purification of the crude products was carried out by column chromatography using silica gel. Analytical TLC was performed on a silica gel GF 254 plate. The TLC plates were visualized under ultraviolet (UV, 254 nm) light or by staining with PMA or CAM. NMR spectra were recorded on a 400 or 500 MHz NMR spectrometer in CDCl 3. Proton chemical shifts are expressed in parts per million (ppm, δ scale) and are referenced to residual protium in the NMR solvent (CDCl 3 , δ 7.26). Data for 1 H NMR are reported as follows: chemical shift, multiplicity (s=singlet, d=doublet, t=triplet, q=quartet, m= multiplet, br=broad), coupling constant (J) in Hertz, and integration. Carbon chemical shifts are expressed in parts per million (ppm, δ scale) and are referenced to the carbon resonance of the NMR solvent (CDCl 3 , δ 77.16). Infrared (IR) spectra were recorded on an ATR/FTIR spectrometer as a thin film on a composite of zinc selenide and diamond crystal and only major functional group peaks are reported in cm-1. High-resolution mass spectra (HRMS) were obtained on a high-resolution Q-TOF mass spectrometer (ionization mode: ESI). Commercially available reagents and solvents were used without further purification. Diynones 1a-1f 1,2 and 1g-1h, 3 as well as diene 2d 4 were synthesized according to reported procedures. S3 General Procedure for Diels-Alder reaction of diynones: To a solution of diynone 1 (1.0 equiv.) and diene 2 (5.0 equiv.) in dichloromethane (ca. 0.05-0.15 M) was added dimethylaluminum chloride (1.0 M in hexanes, 1.0 equiv.) slowly over 10 minutes. The reaction mixture was stirred at room temperature for 1-5 h, quenched with dilute aq. NaHCO 3 , dried over anhydrous MgSO 4 and filtered. The solvent was removed in vacuo and the crude product was purified by column chromatography (silica gel).

A new synthetic methodology has been developed for the synthesis of dihydroisobenzofuran carboxaldehyde derivatives. The reaction proceeds by a silver‐catalyzed protodesilylation/5‐exo‐dig cyclization/oxidation reaction to provide a broad scope of products with yields ranging from 55–91 %. Control experiments show that protodesilylation precedes the 5‐exo‐dig cyclization step in the catalytic cycle. The synthetic utility of these highly functionalized products was showcased through a number of chemoselective chemical transformations.