Mild, Racemization Free Cleavage of Ketone SAMP-Hydrazones with Oxalic Acid - Recycling of the Chiral Auxiliary

Abstract

Cleavage of ketone SAMP-hydrazones 1a-f with a saturated aqueous oxalic acid solution gives the corresponding ketones 2a-f in excellent yields and with high enantiomeric purity (ee = 90 -99%). The chiral auxiliary SAMP is recovered from the aqueous phase in good yield (85%) and with unchanged enantiomeric purity. This racemisation free cleavage procedure is compatible with functionalities sensitive to oxidative cleavage conditions, such as ozonolysis, or to strong acids.

The Dihydroxyacetone Unit—A Versatile C3Building Block in Organic Synthesis

“…[33a, 39] However, not only alkyl halides can be used as electrophiles for a-alkylation reactions. We could show that the reaction also proceeds with tosylaziridine (Scheme 14).…”

Asymmetric Synthesis of 2‐Amino‐1,3‐diols and D‐erythro‐Sphinganine

“…[6] In the first step the SAMP-hydrazone (S)-1 was alkylated in the α-position. [7] Subsequently, the chiral auxiliary was removed by treatment with a saturated aqueous solution of oxalic acid [8] to afford the acetal-protected Scheme 1. a) tBuLi, THF, Ϫ78°C, then RX, Ϫ100°C; b) aq. oxalic acid; c) -Selectride  , THF, Ϫ78°C; d) MsCl, CH 2 Cl 2 , Et 3 N, 0°C Ǟ room temp.…”

“…R t ϭ 11.83 min (CP-Sil-8, 100Ϫ10Ϫ300 4, 29.5, 63.9, 65.7, 70.3, 71.5, 73.5, 98.9, 127.6, 127.8, 128.1, 138.6 ppm 13 C NMR (100 MHz, CDCl 3 ): δ ϭ 14. 1, 18.4, 22.7, 24.9, 29.3, 29.5, 29.6, 29.6, 29.7, 31.3, 31.9, 65.0, 66.2, 72.0, 98. 1, 28.3, 44.6, 58.1, 62.3, 69.9, 99.1, 119.3, 128. (7), 69 (28), 65 (5), 59 (100), 56 (8), 55 (7), 54 (8), 53 (28), 45 (15). C 9 H 14 BrN 3 O 2 (276.13): calcd.…”

Asymmetric Synthesis of 2‐Mono‐ and 2,3‐trans‐Disubstituted Azetidines

“…This was accomplished by heating the hydrazines with an excess of borane tetrahydrofuran complex according to a standard procedure developed in our group. [28] Purification by flash column chromatography afforded the pure amines 4 in good yields (64Ϫ92%) as shown in Table 3. Table 3.…”