Fifty Years of (Benz)oxaphospholene Chemistry

Abstract

The first synthesis of benzoxaphospholenes dates back to the 1960s. Since then,t he structuralv ariety of reported (benz)oxaphospholenesh as steadily increased. Organophosphorusc ompounds have caught the interesto fs ynthetic chemists for ac ouple of decades now because of their interesting biological properties. Oxaphospholenes,i n particular,c ould serve as carbohydrate mimetics, and benzoxaphospholenes have been reported to possess bactericidal, insecticidal, herbicidal, and fungistatical properties. Transesterification reactions and addition of phosphorus nucleophiles to carbonylc ompoundsw ere reaction types that led to the production of the first (benz)oxaphospholenes.When it was discovered that allenylphosphonates could easily be obtainedf rom propargyl alcohols and dialkylh alophosphites, the electrophile-induced cyclization reaction of these allenylphosphonate precursors resulted in ah uge boom in the amounto fr eports on oxaphospholene synthesis. To this day,t his methodi ss till frequently used. Ring-closing metathesis and Horner-Wadsworth-Emmons reactions have also provent heir potentialf or the preparation of oxaphospholenes. In recent years, Pd, Rh and Au-catalysis have made their entry,g enerating (benz)oxaphospholenes from a wide variety of simple substrates. Ac ouple of miscellaneous methods are summarized at the end of the Review.[a] J.

Three-Step Synthesis of Chiral Spirocyclic Oxaphospholenes

“…Moreover, oxaphospholenes have attracted the interest of synthetic chemists for half a century already, and they have been investigated for their fungistatic, antiviral, and antioxidant activities. 19 Even though the halocyclization of (3-cyclohexyl)allenylphosphonates to spirocyclic oxaphospholenes has been known for a few decades, 20,21 this is the first example of the design of such chiral spirocyclic compounds. The synthesis we envisioned is based on three successive transformations from readily available chiral starting materials.…”

“…Inspired by our expertise in oxaphospholene chemistry, − the synthesis of phosphorus-containing allenes , and heterocycles, − we envisioned the synthesis of chiral spirocyclic oxaphospholenes 4 , which may be of interest for the design of new chiral phosphonic acid catalysts. Moreover, oxaphospholenes have attracted the interest of synthetic chemists for half a century already, and they have been investigated for their fungistatic, antiviral, and antioxidant activities . Even though the halocyclization of (3-cyclohexyl)­allenylphosphonates to spirocyclic oxaphospholenes has been known for a few decades, , this is the first example of the design of such chiral spirocyclic compounds.…”

Visible-Light-Induced C(sp2)–P Bond Formation by Denitrogenative Coupling of Benzotriazoles with Phosphites

“…The initial experiment was carried out using 1-(benzoyl)­benzotriazole ( 1aa ) as the model substrate, triethyl phosphite as the phosphorylation agent, and Ir­(ppy) 2 (dtbbpy)­PF 6 as catalyst at room temperature in DMSO. To our delight, after irradiating with 15 W blue LEDs for 10 h, the product 3aa , an important intermediate in the synthesis of benzoxaphospholenes, was obtained in 61% yield (for details, see Supporting Information (SI), Table S1). After a series of condition screenings, we found CH 3 CN to be the optimal solvent, Ir­(ppy) 2 (dtbbpy)­PF 6 to be the most efficient catalyst, and P­(OEt) 3 (3.0 equiv) to be the best phosphorylation agent, respectively (SI, Tables S2 and S3).…”