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I was reading a study on the synthesis of Diethyl Methylphosphonite and it mentioned three ways to make it. The first way they said was costly and complicated. The second way was then explained in the study alongside methods on how to improve it. This is all that was said about the third way "the third means is the reduction of Diethyl Methylphosphonate. This method is strict for the selection of reducing agent."

Nothing else was explained. I was wondering what the reducing agent might be? And what the steps were to perform this synthesis? It seems to me that a reduction reaction would be a lot more straightforward than the method provided. Unless expense might be the factor in play. Thanks in advance for anyone who can answer.

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This paper1, like the one given in the comments by Waylander, is behind a paywall but also indicates the use of boranes, specifically $\ce{BH3/B2H6}$. According to a graphical abstract given in front of the paywall, the Lewis-acidic boron coordinates to phosphorus to achieve the reduced state. The fate of the oxygen from the $\ce{P=O}$ bond is not shown but this probably also ends up coordinated with a boron atom. When the $\ce{P – B}$ bond is hydrolyzed the oxygen from the water is again coordinated to boron leaving the phosphorus bonded to hydrogen and reduced.

Reference

  1. Sowa, S. and Pietrusiewicz, K.M. (2019), "Chemoselective Reduction of the P=O Bond in the Presence of P–O and P–N Bonds in Phosphonate and Phosphinate Derivatives". Eur. J. Org. Chem., 2019: 923-938. https://doi.org/10.1002/ejoc.201801518
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