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5.8.1.2 Reduction with Phosphinic Acid and Its Derivatives

DOI: 10.1055/sos-SD-206-00491

Yorimitsu, H.; Oshima, K.Science of Synthesis: Water in Organic Synthesis, (20121652.

Tributyltin hydride and tris(trimethylsilyl)silane are undoubtedly useful mediators in radical chemistry; however, the toxicity of difficult-to-remove tin compounds and the cost of group 14 metal hydrides are serious drawbacks. Since 1990, phosphinic acid, commonly called hypophosphorous acid, and its derivatives have emerged as inexpensive and readily removable radical reducing agents.[‌11‌,‌14‌‌16‌,‌28‌‌30‌] Nowadays, phosphinic acid derivatives are widely used as reliable mediators in organic synthesis. Barton pioneered the use of phosphinates (hypophosphites) as tin hydride substitutes.[‌31‌,‌32‌] Because aqueous phosphinic acid is commercially available, an aqueous medium is likely to be the natural choice in which to perform a radical reduction with this acid; however, since phosphinic acid is a strong acid (pKa 2), a base needs to be added for neutralization. Many bases, including sodium hydrogen carbonate and tertiary amines, serve well in this context. Sodium phosphinate is commercially available, inexpensive, and almost neutral; it is also worth noting that such a phosphinate salt is a far better radical mediator than the parent acid.[‌33‌,‌34‌]

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Mee eeeee ee eeeeeeeeee eee eeeeeeeeeee-eeeeeeee eeeeeee eeeeeeeeee ee eee ee eeee ee eee eeeee 88 eeeee eeeeeeee, eee ee eeeee eeeeeeeeeeee. Meeee 8 eeeeeeeeee eee eeeeeeeee; eeee, eeeee eeeeeee eee eeeeeeee eee ee eeeeeee eeeeeee eeeee eeeeeeeee eee eeeeeeeeee. Meee eeeeeee eee eeeeeeee eeeeeeeeee ee eeee eeeeeeee, eee eeee eeeeeeee eee eeee eeeeeeee eee eeee eeeeeee eeeeeeeeee eeeeeeeeee eeeeeeeeeee. Meeeeeeeeeee eee eeeeeee MeeeeeMeMeeeee eeeeeeeeee. Meeee eeeeeeeeeee eee eeee eeee eeeeeeeeee eee eeeee eeeeeee eeeeeeeeeee ee eeeeeeee; ee eeeeeeee, eee eeeeeeeeee ee eeeee eeeeeeeee eeeeeee eeeeeeeeee eeee.

Meeee 8 Meeeeeee ee Meeeeeeee Meeeeeeeee ee Meeeeeeeeee-Meeeeeee Meeeeee Meeeeeeeee

Meeeeeeee Meee Meeeeeeeee
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Meeee 8 Meeeeeeeeee-Meeeeeee Meeeeee Meeeeeeee[‌88‌‌88‌]

Meeee Meeeeeeee Meeeeeeeee Meeeeee Meeee (%) Mee
8 M8MM8, Me8M, MMMM, ee eeeeeee, eeeeee 88 [‌88‌,‌88‌]
8 [Me(MM8)88MMe8]MM8M8, MMMM, M8M, eeeeee 88 [‌88‌]
8 M8MM8, Me8M, MMMM, ee eeeeeee, eeeeee 888 [‌88‌,‌88‌]
8 M8MM8, Me8M, MMMM, ee eeeeeee, eeeeee 88 [‌88‌,‌88‌]
8 M8MM8, Me8M, MMMM, ee eeeeeee, eeeeee 888 [‌88‌,‌88‌]
8 M8MM8, Me8M, MMMM, ee eeeeeee, eeeeee 88 [‌88‌,‌88‌]
8 Me8MMM8M8, MMMM, M8M, 88°M 88 [‌88‌]
8 Me8MMM8M8, MMe8, M8M, ee 88 [‌88‌]
8 M8MM8, Me8M, MMMM, ee eeeeeee, eeeeee 88 [‌88‌,‌88‌]
88 Me(MM8)88MM8M M8MM8, MeMMM8, MMMM, ee MeMM, eeeeee Me(MM8)88Me 888 [‌88‌,‌88‌]
88 Me(MM8)88MM8M M8MM8, MeMMM8, MMe8, ee MeMM, ee Me(MM8)88Me 88 [‌88‌,‌88‌]
88 M8MM8, MeMMM8, MMMM, ee MeMM, eeeeee 88 [‌88‌,‌88‌]
88 M8MM8, MeMMM8, MMMM, ee MeMM, eeeeee 88 [‌88‌,‌88‌]
88 [Me(MM8)88MMe8]MM8M8, MMMM, M8M, eeeeee 888 [‌88‌]
88 M8MM8, MeMMM8, MMe8, ee MeMM, ee 88 [‌88‌,‌88‌]
88 M8MM8, MeMMM8, MMMM, M8M, eeeeee 88 [‌88‌]
88 M8MM8, MeMMM8, MMMM, M8M, eeeeee 88 [‌88‌]
88 M8MM8, MeMMM8, MMMM, M8M, eeeeee 88 [‌88‌]
88 M8MM8, MeMMM8, MMMM, M8M, eeeeee 88 [‌88‌]
88 eMeMMMeMM8M M8MM8, MeMMM8, MMMM, M8M, eeeeee eMeMM8MM8M 88 [‌88‌]
88 M8MM8, MeMMM8, MMMM, M8M, eeeeee 88 [‌88‌]
88 M8MM8, MeMMM8, MMMM, M8M, eeeeee 88 [‌88‌]

Meeeeeeeeeee eee ee eeee ee eeeeeee eeeeeeeeeeeeee eeeeeeeee eeeeeee eeeeeeeeeeee ee eeeeeee eeeee eeeee eeeeeee eeeeeeeeee eeeeeeeee 8,8-eeeeee[8-(8,8-eeeeeeeeeeeeeee-8-ee)eeeeeee] eeeeeeeeeeeeeee (8, MM-888) (Meeee 8).[‌88‌,‌88‌,‌88‌‌88‌] Mee eeeeeeeeeee-eeeeeeee eeeeeeeeeeee ee eeee-eeeeeeee eeeeeeeeeee eee eeeeeeeeeeee ee eeeeee eeeeeee eee, eee ee ee eeeeeeeee eee eeeeeeee eeeeee ee ee eeeeee ee eeeeeee eeeeeeeee. Meeeeee eeeee-eeeeeee eeeeeeeeee eee ee eeeeeee ee eeeee,[‌88‌] eeeeeeeeeee eeeeeeeeee eeeeee ee eeeeeee ee eeeeeee eeeeeee,[‌88‌,‌88‌] ee ee eeeee eeee eee eee ee e eeeeeeeeee.[‌88‌‌88‌]

Meeeeeeeeeeeee eeeeeee eeeeeeeee ee eeeeeee eeeeeee ee eeeeeeeee eeeeeee eeee eeeeeee ee eeeeeee eeeee eeee eee eee ee eeeeeeeeeee eeeee eee eeeeeeeeee eeee ee 8,8-eeeeee(8-eeeeeeeeeeee eeee) (8, MMMM),[‌88‌,‌88‌,‌88‌,‌88‌,‌88‌] eeee eeeeeeee eeeeeee ee eee eeeeeeeeeee eeeeeee 8 eee eeeee ee Meeeee 8.[‌88‌,‌88‌] Meee, eee eeeeeeee ee e eeeeeeeeee ee eeeeeeeeeee ee eeeeeee eee eeee eeeeeeeee eeeeeee eeeeeeeee.

Meeee 8 Meeeeee Meeeeeeeeeee eeee Meeeeeeeeeee[‌88‌,‌88‌,‌88‌,‌88‌,‌88‌]

Meeee Meeeeeeee Meeeeeeeee Meeeeee Meeee (%) Mee
8 M8MM8, MeMMM8, MMMM, M8M, eeeeee 88 [‌88‌]
8 M8MM8, MeMMM8, MMMM, ee MeMM, eeeeee 88 [‌88‌,‌88‌]
8 M8MM8, MeMMM8, MMMM, ee MeMM, eeeeee 88 [‌88‌,‌88‌]
8 M8MM8, MeMMM8, MMe8, ee MeMM, ee 88 [‌88‌,‌88‌]
8 M8MM8, MeMMM8, MMMM, ee MeMM, eeeeee 88 [‌88‌,‌88‌]
8 M8MM8, MeMMM8, MMe8, ee MeMM, ee 88 [‌88‌,‌88‌]
8 M8MM8, MeMMM8, MMMM, ee MeMM, eeeeee 88 [‌88‌,‌88‌]
8 M8MM8, MeMMM8, MMe8, ee MeMM, ee 88 [‌88‌,‌88‌]
8 8-eeeeeeeeeeeeeeeee eeeeeeeeeee, MMMM, MM-888,e M8M, 88°M 88 [‌88‌]

e MMMM=eeeeeeeeeeeeeeeeeeeeee eeeeeee; MM-888=8,8-eeeeee[8-(8,8-eeeeeeeeeeeeeee-8-ee)eeeeeee] eeeeeeeeeeeeeee (8).

Meeeee 8 Meeeeeeeeeeeee Meeeeee Meeeeeeee ee Meeeeeeee Meeeeee[‌88‌,‌88‌]

Meeeeeeeeee 8

M8 M8 Meeeeeeeeee Meeee (%) Mee
Me MM8Me 8-eeeeeeeeeeeeeeeee eeeeeeeeeee, MMMM, MMMM, 888°M 88 [‌88‌]
Me MM8Me 8-eeeeeeeeeeeeeeeee eeeeeeeeeee, MMMM, MMe8, 88°M 88 [‌88‌]
Me MM8Me [Me(MM8)88MMe8]MM8M8, MMMM, eeeeee 88 [‌88‌]
Me MM8Me 8-eeeeeeeeeeeeeeeee eeeeeeeeeee, MMMM, MMMM, 88°M 88 [‌88‌]
Me MM 8-eeeeeeeeeeeeeeeee eeeeeeeeeee, MMMM, MMMM, 88°M 88 [‌88‌]
Me Me 8-eeeeeeeeeeeeeeeee eeeeeeeeeee, MMMM, MMMM, 88°M 88 [‌88‌]
eMe MM8Me [Me(MM8)88MMe8]MM8M8, MMMM, eeeeee 88 [‌88‌]
(MM8)8MM8M MM8Me [Me(MM8)88MMe8]MM8M8, MMMM, eeeeee 88 [‌88‌]

e MMMM=eeeeeeeeeeeeeeeeeeeeee eeeeeee; MMMM=8,8-eeeeee(8-eeeeeeeeeeee eeee) (8).

Meeeeeeeeeeeeeee eeeeeeeeeeeeee eeeeeee eeeeeeee ee ee eeeee eeeeeee ee e eeeeeeeeee eeeee eeeee eeeee eeeee eeeee eeeeee eeeeeeeeeee eeeee eeeeee ee eeee eeee e eeeeeeee eeeeeeee eeee ee 88 (Meeeee 8).[‌88‌] Meeeeeee eeee ee ee eeeeeeeee eeeeeeeeeee, eee eeeeeeeeeee eee e eeeee eeeeee ee e eeeeee eeeee ee e eeeeeeee.

Meeeee 8 Meeeeeeeeeeeeeee Meeeeee Meeeeeee ee e Meeeeeeeee Meeee Meeee[‌88‌]

Mee eee(M-eeeeee eeeeeeeeeeeeeee) eeeeee ee eeeeeee eeeee eee ee eeeeeee ee eee eeeeeeeeeeeee eeeeeee eeeee eeeeeeeeeee eeeee (Meeee 8).[‌88‌,‌88‌,‌88‌] Me eeeeeeeeeee eeeeee ee eeeee eeeeeeeee. Mee eeeeeeeee eeeeeee eeeeeee M-eeeeeee eeeeeeeeeeeeeeeee, eeeeeee (M)-eeeeeeeeeee eeeeeeeeeee eee eeeeee ee eee eeeeeeeee ee eeeeee-eeeee eeeeee eeee eeeeeeeeeee.

Meeee 8 Meeeeeeee ee Meeeeee eeee Mee(M-eeeeee eeeeeeeeeeeeeee) Meeeee ee Meeeeee Meeee[‌88‌,‌88‌]

Meeee Meeeeeeee Meeeeeeeeee Meeeeee Meeee (%) Mee
8 8-eeeeeeeeeeeeeeeee eeeeeeeeeee, MMMM, 88°M 88 [‌88‌]
8 8-eeeeeeeeeeeeeeeee eeeeeeeeeee, MMMM, 88°M 88 [‌88‌]
8 8-eeeeeeeeeeeeeeeee eeeeeeeeeee, MMMM, 88°M 88 [‌88‌]
8 [Me(MM8)88MMe8]MM8M8, eeeeee 88 [‌88‌]
8 8-eeeeeeeeeeeeeeeee eeeeeeeeeee, MMMM, 88°M 88 [‌88‌]
8 [Me(MM8)88MMe8]MM8M8, eeeeee 88 [‌88‌]
8 8-eeeeeeeeeeeeeeeee eeeeeeeeeee, MMMM, 88°M 88 [‌88‌]
8 [Me(MM8)88MMe8]MM8M8, eeeeee 88 [‌88‌]

e MMMM=eeeeeeeeeeeeeeeeeeeeee eeeeeee.

M eeeeeeeeeee ee eeeeeeeeee eeee, eeeeee eeeeeeee eeeeeeeee, eee eeeeeeeeeeeeeeeeeeeeee eeeeeee eee eeeeeee eeeeeee eeeeeeeeeeeeee ee eeeee eeeeeee ee eeeeeee eeeee eeeee ee eeeeeeeeee ee eeeeee eeeeeeee. Mee eeeeeee, eeeeeeeeeeeeeee eeeeeee eeeeeeeeeeeeeeeeeeeee eeee ee 88% eeeee ee eeee eeeeeeee (Meeeee 8).[‌88‌]

Meeeee 8 Meeeeee Meeeeeeeeeeee ee Meeeeee Meeee[‌88‌]

Meeeeeeeee eeeeeeeeee eeee eeeeeee eee eeeeeee eeeeeeeeeee ee ee eeeeeee eeeeee eeee ee eee eeeeee 88 (Meeeee 8).[‌88‌] Me eeeeeee eeee eeeeee ee eeeeeeeee eeeeeeeeeeeee, eeeeeee ee eeeeeeeee eeeee eee eee eeee eeeee; eeeeeeeee, eeeeeee eeeeeeee eeeeeeeeeee eeee e eeeeeee eeeeeeee eeeeeeee eeee eee eeeeeee eeeeeeeee eeeeeeeeeee.

Meeeee 8 Meeeeee Meeeeeeeeee eeee Meeeeeeeee Meeeeeeeeee[‌88‌]

Meeeeeeeeeee Meeeeeeee

Meeeee Meeeeee (Meeee 8, Meeee 88):[‌88‌]

MMMMMMM: Meeeeeeeee eeee ee eeeeeeeee eee eeeeee eeeee ee eee eeee ee eeeeeee.

8-Meeeeeeeee eeeeeee (8.88e, 8.8eeee), MMMM (88ee, 8.88eeee), eee MeMMM8 (8.8e, 88eeee) eeee eeeeee ee e eeeee eee MeMM (8eM) eee eeeee. Meee, 88% ee M8MM8 (8.8eM, 88eeee) eee eeeeeeeee eeeeeeeeee ee eee eeeeeee eeeeeeee eee eee eeeee eee eeeeeee eeee eeeee. Mee eeeeeee eee eeeeee ee eeeeee eee 8e, eee eeee eeeeee eee eeeeee eeee eeeee (88eM). Mee eeeeeee eee eeeeeeeee eeee MeMMe (8×88eM). Mee eeeeeeee eeeeeee eeeee eee eeeee (Me8MM8) eee eeeeeeeeeeee eeeee eeeeeee eeeeeeee. Meeeeeeeeeeeeee eeeeeeeeeeee (eeeeee eee) eeeeeeee eee eeeee eeeeeeee; eeeee: 8.888e (88%).

8-Meeee-8,8-eeeeeeeeeeee[8.8.8]eeeeee (Meeee 8, Meeee 8); Meeeeee Meeeeeeee:[‌88‌]

MMMMMMM: Meeeeeeeee eeee ee eeeeeeeee eee eeeeee eeeee ee eee eeee ee eeeeeee.

MeMM (8eM) eee MeMMM8 (8.88e, 88eeee) eeee eeeeee ee e 88-eM eeeee eee 88% ee M8MM8 (8.8eM, 88eeee) eee eeeee eeeeeeee ee eee eeeeeeeeee eeee eeeeeeee eeeeeeee. Mee eeeeeee eee eeeeeee eee 88eee. (8M*,8M*)-8-(Mee-8-eeeeeee)-8-eeee-8,8,8,8-eeeeeeeeee-8M-eeeee (8.88e, 8.8eeee) eee MMMM (88ee, 8.88eeee) eeee eeeeee ee e eeeeeeeee eeeee, ee eeeee eee eeeee eeeeeeeeeee eeee eee eeee eeeee. Mee eeeee eee eeeeeee eeee eeeee eee eee eeeeeee eee eeeeee ee eeeeee eee 88eee. Meeee eeeeeee, eee eeeeeee eee eeeeee eeee eeeee (88eM), eee eee eeeeeee eee eeeeeeeee eeee MeMMe (8×88eM). Mee eeeeeeee eeeeeee eeeeee eeee eeeee (Me8MM8) eee eeeeeeeeeeee eeeee eeeeeee eeeeeeee. Meeeee eeeeeeeeeeeeee (eeeeee eee) eeeeeeee eee eeeee eeeeeeee; eeeee: 8.888e (88%).

8-Meeeeeeeeeeeeee Meeeee Meeeeee (8, M8=Me; M8=MM8Me); Meeeeee Meeeeeeee:[‌88‌]

Meeeeeeeeeeeeee (8.888eM, 8.88eeee), eeeeee eeeee eeeeeee (88ee, 8.88eeee), MMMM (888ee, 8.88eeee), e 8.88M eeee ee 8-eeeeeeeeeeeeeeeee eeeeeeeeeee ee 8,8-eeeeeee (8.88eM, 8.88eeee), eee MMMM (8; 88ee, 8.88eeee) eeee eeeee ee eeeeeeee M8M (88eM). Mee eeeeeee eee eeeeeee ee 888°M eee 8.8e. Meeee eeeeeee, eee eeeeeeeee eeee eee eeeeeee eeee MeMMe (88eM), eee eee eeeeeee eeeee eee eeeeee eeee M8M (88eM) eee eeee eeee eeeee (88eM), eeeee (MeMM8), eee eeeeeeeeeeee. Mee eeeeeee eee eeeeeeee ee eeeeeeeeeeeeee (eeeeee eee, eeeeee/MeMMe 88:8) ee eeeeee eee eeeee eeeeeeee; eeeee: 888ee (88%).

eeee-(M)-8,8-Mee(8,8-eeeeeeee-8,8-eeeeeeee-8-ee)eeeeee (Meeee 8, Meeee 8); Meeeeee Meeeeeeee:[‌88‌]

8,8:8,8-Me-M-eeeeeeeeeeeeee-8,8-eee-M-[(eeeeeeeeeeeeee)eeeeeeeeeeeee]-e-eeeeeeee (88ee, 8.88eeee), 8-eeeeeeeeeeeeeeeee eeeeeeeeeee (888ee, 8.88eeee), eee MMMM (888ee, 8.88eeee) eeee eeeee ee eeeeeeee M8M (8eM). MMMM (8; 8×88ee, 8.88eeee) eee eeee eeeee ee 8-e eeeeeeeee ee eee eeeeeee, eeeee eee eeee ee 88°M. Mee eeeeeeeee eeeeeee eee eeeeee ee ee eee eeeeeee eeee MeMMe (88eM), eee eeee eee eeeeeeeee eeeeeee eeeee eee eeeeee eeee M8M (88eM) eee eeee eeeee (88eM). Mee eeeeeee eeeee eee eeeee (MeMM8) eee eeeeeeeeeeee, eee eee eeeeeee eee eeeeeeee ee eeeeeeeeeeeeee (eeeeee eee, eeeeee/MeMMe 8:8) ee eeeeee eee eeeee eeeeeeee; eeeee: 88ee (88%).

References