Science of Synthesis

Whitehead, A.; Sieck, S. R.; Mukherjee, S.; Hanson, P. R., Science of Synthesis, (2005) 21, 917.

Diastereoselective reductions of acylphosphonates occur with moderate selectivity to generate the corresponding α-hydroxy phosphonates. For example, reduction of acylphosphonate ‌35‌ (which is obtained from the acid chloride ‌34‌) with sodium cyanoborohydride gives diethyl (2S)-1-hydroxy-3-methyl-2-(phthalimido)butylphosphonate (‌36‌) as an 85:15 diastereomeric mixture (‌Scheme 11‌).[‌37‌] Similarly, in the case of acylphosphonate derivatives of cytidine arabinoside, sodium cyanoborohydride reduction leads to a 5:1 mixture of α-hydroxy phosphonate epimers.[‌38‌] Reduction of α-oxo-β-phthalimido phosphonates with borane–methyl sulfide complex provides products with diastereomeric ratios as high as 10:1.[‌39‌] When catecholborane and catalytic amounts of an oxazaborolidine are employed, a single diastereomer for the reduced product is observed.

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References