Formal Synthesis of 3-Deoxy-d-manno-2-Octulosonic Acid (KDO) via a Highly Double-Stereoselective Hetero Diels−Alder Reaction Directed by a (Salen)Co^II Catalyst and Chiral Diene

Abstract

This paper presents a formal total synthesis of 3-deoxy-D-manno-2-octulosonic acid (KDO) based on a highly double-stereoselective hetero Diels-Alder reaction between an electron-rich diene and ethyl glyoxylate catalyzed by (Salen)Co(II) complex, a new catalyst for Diels-Alder reactions. A facial specific hydroboration followed by oxidative workup leads to a diol system with the trans-diequatorial arrangement of hydroxyl groups at the C-4 and C-5. Inversion of the configuration of the C-5 hydroxyl group in 12 and then ketal formation afford the desired target diisopropylidene-2-deoxy-KDO methyl ester (18), which can be converted to KDO according to the literature procedure.

Enantioselective Diels−Alder Reactions of Optically Active (Buta-1,3-dien-2-yl)(salen)cobalt(III) Complexes

“…These con- formers have dihedral (torsion) angles around the C(38)ϪC(39) and C(88)ϪC(89) bonds of 68Ϫ70°, similar to (dienyl)(glyoxime)cobalt complexes we have reported previously. [14] The Co(1)ϪC(38) and Co(2)ϪC(88) distances of 1.962(9) Å and 2.007 (13) Å are also similar to those seen in the glyoxime ligand series. [14] In solution, we saw no 1 H NMR line broadening over a temperature range of 25 to Ϫ63°C.…”

“…[11] Jacobsen and co-workers have reported the use of these (salen)Co complexes as catalysts for enantioselective epoxide ring opening [12] and their use as hetero DielsϪAlder catalysts has been reported by Wu et al in 1998. [13] Scheme 1 Leung et al reported that they reduced the (salen)Co II complexes 2a, 2b with sodium amalgam and treated the corresponding anion with unspecified alkyl halides. [11] However, they could not isolate the presumably formed alkylation products.…”

“…The solid-state structure approximates to a centrosymmetric arrangement in space group P1. The two crystallographically independ- (7) 1.304(9) N(51)ϪC(57) 1.292(9) N(2)ϪC (14) 1.291(9) N(52)ϪC(64) 1.305(9) N(1)ϪC (8) 1.486 (7) N(51)ϪC(58) 1.484(7) N(2)ϪC (13) 1.494 (7) N(52)ϪC(63) 1.471(7) C(6)ϪC (7) 1. those we have observed previously for cobaltϪsp 2 -carbon bonds. [2,3,14] Crystal data and structure refinement parameters are provided in Table 3.…”

“…The red-orange crystals were washed with ice-cold methanol (25 mL, 2 ϫ). [13] (S,S)-(؉)-Cobalt(II) Complex 2b: The reaction described above was repeated with (S,S)-(ϩ)-N,NЈ-bis(3,5-di-tert-butylsalicylidene)cyclohexane-1,2-diamine 1b, and 2b (33. 1 mmol) in freshly distilled THF (10 mL) was added over 5 min, and the mixture was stirred at Ϫ78°C for 2 h, allowed to warm to 25°C, and stirred for an additional 18 h. The reaction mixture was vacuum-filtered through a coarse fritted funnel into degassed ice-cold aqueous sodium hydroxide solution (500 mL, 0.25 ) and stirred for 2 h. The dark green product was collected by vacuum filtration.…”

Synthesis, characterization, solvatochromic behavior and crystal structures of complexes [CoIII(salophen)(thioacetamide)2]ClO4 and [CoIII(salophen)(thiobenzamide)2]ClO4

“…Quadridentate Schiff base cobalt complexes have been widely studied, particularly as homogeneous catalysts, oxygen carriers, and models of compounds with biological function [1][2][3][4][5][6][7][8][9][10][11][12]. It is known that variation of the size and nature of the ligand can be responsible for changes in the coordination geometry around central metal ions.…”