Organophosphorus Compounds, Part 149. Preparation of 1,3-Oxaphospholes by Transition Metal-Catalyzed Reactions of α-Diazo-β-dicarbonyl Compounds with tert-Butylphosphaacetylene

Abstract

In the presence of Rh 2 (OAc) 4 as catalyst the cyclic a-diazo-b-dicarbonyl compounds 7a-c react with tert-butylphosphaacetylene 2 under elimination of nitrogen to furnish the 1,3-oxaphosphole derivatives 8a-c. The feasible competing reaction with formation of the 1,2,4-diazaphospholes 9a-c has not been observed.The class of the 1,3-oxaphospholes still constitutes a relatively unknown area in the fertile field of heterophosphole chemistry. 2 Currently, only two separate routes to nonbenzo-condensed 1,3-oxaphospholes have been described: Thus, 1,3-oxaphosphole derivatives can be obtained either by reaction of phosphaacetylenes with Fischer-type chromium carbene complexes or by 1,3-dipolar cycloaddition reactions of isomünchnones with the phosphaacetylenes. [3][4][5] Although the reaction of the isomünchnone 5 with the phosphaacetylene 2 furnishes the 1,3-oxophosphole derivative 6 in very good yield in a highly specific reaction, 3,4 the 1,3-oxaphosphole 3 prepared from the carbene complex 1 is isolated in merely 35% yield. 5 The reason for this low yield is the fact that the reaction is not specific for formation of the 1,3-oxaphosphole but is instead accompanied by a side reaction furnishing the phosphaarene species 4. 5 By use of catalytic amounts of rhodium(II) acetate we have now successfully realized reactions between the cyclic a-diazo-b-dicarbonyl compounds 7 and tert-bu- Scheme 1Downloaded by: National University of Singapore. Copyrighted material.

New Route to Access an Acyl‐Functionalized Phosphasilene and a Four‐Membered Si‐P‐C‐O Heterocycle

“…The angle on the phosphorus atom is comparable to another four‐membered ring with a CP bond (C‐P‐C 76.9(1)°) 21. The t Bu group on the carbon atom is bent toward the oxygen atom and thus away from the phosphorus atom (C17‐C16‐P1: 130.5(2) and 131.1(2)° vs. C17‐C16‐O1: 115.6(2) and 115.2(2)°), which was previously observed for another PCO heterocycle (C‐C‐P: 131.75(14)° vs. C‐C‐O: 113.4(2)°) 20a…”

Organophosphorus Compounds in Organic Electronics

“…In contrast, other heterophospholes, such as 1,3‐thiaphospholes are thought to be aromatic; however, recent calculations also indicate that the HOMO in these compounds is mainly located on the P=C fragment . In the solid‐state structures of some 1,3‐oxaphospholes, enhanced aromaticity is anticipated from the observed P=C bond length, which falls in between a typical single and double bond . These theoretical and experimental findings clearly show that the bonding situation in phospholes largely depends on several factors, such as their substituents, enforced planarity, and other electronic factors.…”

“…[32] In the solid-state structures of some 1,3-oxaphospholes,e nhanced aromaticity is anticipated from the observed P=Cb ond length, which falls in between at ypical single and double bond. [33] Theset heoretical and experimental findings clearly show that the bonding situation in phospholes largely depends on severalf actors, such as their substituents,e nforced planarity,a nd other electronic factors. Moreover the introduction of additional heteroelements can lead to drastic alterations of the parent system.…”

Transition Metal-Mediated Synthesis of Monocyclic Aromatic Heterocycles

“…534 Interestingly, Regitz showed that the Rh(II)-catalyzed reaction of α-diazocarbonyl compounds with tert -buthylphosphaacetylene furnishes 1,3-oxaphospholes. 535 …”