A Remarkable Catalyst-Free Photochemical Alkene Hydrophosphination with Bis(trimethylsilyl)phosphonite

Abstract

This publication delves into a comprehensive exploration of a new synthetic route to functionalized phosphorus-derived compounds. Bis-(trimethylsilyl)-phosphonite HP-(OSiMe₃)₂, prepared in a high yield from H₃PO₂, was found to be an excellent reagent for hydrophosphination of activated, unactivated, and amino acid-derived olefins under UV irradiation and catalyst-, solvent- and glovebox-free conditions. The resulting phosphorus trivalent compounds have been subjected to postfunctionalization, leading to the formation of H-phosphinate, phosphonate, and thiophosphonate end products in good to excellent yields. With a combination of experimental and theoretical calculations, the mechanism for this hydrophosphination reaction has been investigated, revealing a radical process.

Keywords: P-chemicals; bis(trimethylsilyl)phosphonite; catalyst-free; divergent synthesis; hydrophosphination; photochemistry.

1

Present work encompasses the hydrophosphination with BTSP and post-transformations to organophosphorus.

2

Method A: 1) Drying, 2) BSA (2 equiv), quantitative. Method B: 1) aq. ammonia, filtration, 88%, 2) HMDS (1.1 equiv), quantitative. Method C: 1) Drying, 2) HMDS (1.1 equiv), 76% conversion. Method D: 1) aq. ammonia, filtration, 88%, 2) BSA (2 equiv), 83% conversion.

3

³¹P­{¹H} and ³¹P NMR monitoring of the hydrophosphination reaction between BTSP 2b (1.43 mmol, 1 equiv) and hexene (2.86 mmol, 2 equiv).

4

On/off experiment: BTSP 2b (1.43 mmol, 1 equiv) and hexene (2.86 mmol, 2 equiv). ³¹P­{¹H} and ³¹P NMR monitoring.

5

Mechanistic studies support the radical pathway. ^a Full conversion after 9h45 of reaction. ^b Conversion was based on ³¹P NMR.

6

Calculated minimum-energy pathway for a model reaction.

7

Reactivity of HP­(OSiMe₃)_{2 2} toward 4-vinyl-cyclohexene, (S)-limonene, and styrene. ^a Isolated yield.

8

Scope of the hydrophosphination procedure leading to H-phosphinates 4a-s salt. Conditions: 2b (1.43 mmol, 1 equiv), alkene (2 equiv for aliphatic or 1 equiv for aromatic substrates), irradiation at 254 nm. ^a Isolated yield. ^b Conversion based on ³¹P NMR.

9

Synthesis of phosphonates 5a-salt, 5e-salt and thiophosphonates 6a-salt, 6e-salt using post-transformations.

10

Synthesis of aminoadipate and glutamate analogues 11–14-salt.