Synthesis of D‐ and L‐2‐Amino‐2‐deoxyarabinose and 1,4‐Dideoxy‐1,4‐iminolyxitol by (C₂ + C₃)‐Nitroaldol Addition with 2‐O‐Benzylglyceraldehyde

Abstract

P-02-C1 angle is less acute than in epo~ides.[~l The most interesting feature of this structure is that it keeps the "memory" of its phosphaalkene precursor. The sum of the W-P-C6, W-P-C1, and Cl-P-C6 angles (357.3') is close to 360°, as in the parent phosphaalkene complex.r3b1 The plane of the oxaphosphirane ring is almost orthogonal to the WPCl C6 mean plane [90.3(0.2)"]. The phosphorus atom appears to retain its initial sp2 hybridization. Even the P-C1 bond [1.778(6) A] is shorter than expected for a normal P-C single bond. The structure of 3 also shows that the epoxidation of the P = C double bond takes place with retention of the initial trans stereochemistry of 1 [C3-P-CI-C6 dihedral angle 161.3(5)"]. However, with the less hindered phosphaalkene complex 2, this retention is not complete. Indeed, the epoxidation of 2 mainly leads to 4.[*] The 'H-NMR spectrum of 4, like that of 3 shows no H-C1-P coupling.r41 Thus, 4 probably has the same trans stereochemistry as 3. However, besides 4 (h31P = +2.9 in C,D,), another compound 5 (h31P = +6.2) is produced in minor amounts (ca. 10%). This compound is probably the cis isomer corresponding to 4. Finally, the main decomposition path of the oxaphosphiranes 3 and 4 in the mass spectrometer involves splitting of the ring into the terminal phosphinidene complex [Mes-P=W(CO),] and the aldehydes RCHO. This process is exactly the reverse of the first described synthesis of this ring."] ExperimentalA solution of m-chloroperbenzoic acid (1.9 g, 1.1 x lo-, mol) in THF (10 mL) was added dropwise to a solution of the phosphaalkene complex 1 (5.3 g, 1 x lo-, mol) in THF (30 mL). The reaction was slightly exothermic. After evaporation of T H E the residue was extracted with hexane. The extract after removal of hexane was recrystallized from pentane/CH,CN. 5.0 g of 3 (-86%). colorless crystals: m.p. 68-69 "C. The same procedure with 2 gave 4 in 40% yield after recrystallization; m.p. 61 -64°C (along with ca 10% of the cis isomer).

Syn-Selective Michael Addition of Nitromethane Derivatives to Enoates Derived from (R)-(+)-Glyceraldehyde Acetonide

“…It was observed that the syn/anti ratio at C-3 in the resulting adducts 5a , 5b , and 5g , as well as the epimeric ratio at the CNO 2 (C-1‘) chiral center in adducts 5b and 5g , was constant, regardless the reaction time and the base employed. Due to the acidity of the hydrogen atoms on the carbon bearing the nitro group, it seems reasonable to assume that formation of these chiral centers is thermodynamically controlled, particularly in light of the report that for aldol addition reactions involving nitronates the stereogenic center bearing the nitro group is easily epimerizable . In contrast, the constant syn/anti ratios seemed to indicate that the chirality at the newly generated center C-3 is kinetically controlled, although the possibility of a rapid equilibration through a retro-Michael−Michael reaction could not, a priori, be completely excluded.…”

A Mesoporous Aluminosilicate Nanoparticle-Supported Nickel–Boron Composite for the Catalytic Reduction of Nitroarenes

“…Traditionally, the synthesis of aromatic amines from their corresponding nitro compounds is performed at high temperatures and pressures, in the presence of hydrogen gas and a metallic catalyst such as Pt, Pd, Fe, Sn, or the well-known Raney nickel (eq ). − …”