Synthesis of Chiral α,δ-Dioxygenated Allylic Stannanes as Reagents for Carbohydrate Synthesis and Homologation

Abstract

The delta-oxygenated allylic stannanes 4.4 and 4.5, prepared through addition of Bu(3)SnLi to gamma-OTBS crotonaldehyde 4.3c followed by etherification of the adduct with TBS-Cl or MOM-Cl, undergo transmetalation with InCl(3) and in situ addition to aldehydes leading to mainly anti adducts 5.1 or 5.2, accompanied by varying amounts of syn diastereomers. Selectivities of >95:5 can be realized with the MOM reagent 4.5 and ynals 4.3d and 4.3e or cyclohexanecarboxaldehyde 4.3a. With enals 4.3b and 4.3c, 80:20 mixtures of anti and syn adducts are formed. The S enantiomer 10.1 of stannane 4.5 has also been prepared as a reagent for carbohydrate synthesis. Accordingly, addition to alpha-ODPS acetaldehyde 10.2 in the presence of InCl(3) leads to the adduct 10.3 as an inseparable 90:10 mixture of anti and syn diastereomers. Dihydroxylation of the OTBS derivative 10.4 affords the potential altrose precursor 10.5 in 81% yield.

Preparation of γ-siloxyallyltributylstannanes and their use in the synthesis of (±)-1-deoxy-6,8a-di-epi-castanospermine

“…2 These behaviours of heterosubstituted allylstannanes have been reviewed by several groups with a special emphasis on the crucial importance of the experimental conditions on the stereochemistry of the reaction [3][4][5] and exploited for syntheses in sugar series. 6,7 As far as we are concerned, we have recently been interested in the allylstannation of glyceraldehyde derivatives through aldopentose syntheses 2 and in the already known allylstannation of iminium salts. 8,9 We successfully applied these methods for the synthesis of polyhydroxypiperidines.…”

Enantioselective Syntheses of Pachastrissamine and Jaspine AviaHydroxylactonization of a Chiral Epoxy Ester

“…According to the synthetic plan, known unsaturated aldehyde 8 21) was subjected to Córdova's asymmetric epoxidation conditions by using D-proline-derived organocatalyst 9 to give epoxy aldehyde 10 in an 80% yield (Scheme 2).…”

“…After 2.5 h, the mixture was filtered through a pad of Celite and the filtrate was concentrated in vacuo. The residue was chromatographed over SiO 2 (hexane/EtOAc (4R,5S)-4-(tert-Butyldimethylsilyloxy)-5-tetradecyldihydrofuran-3-one (21). To a stirred solution of 20 (296 mg, 0.550 mmol) in CH 2 Cl 2 (9.4 ml) containing a phosphate buffer (pH 7.0, 0.1 M, 0.47 ml) was added DDQ (151 mg, 0.660 mmol) at room temperature.…”

Asymmetric Synthesis of Acyclic Amines Through Zr‐ and Hf‐Catalyzed Enantioselective Alkylzinc Reagents to Imines

“…Diethylzinc, dimethylzinc (2.0 M in toluene), Zr(O-i-Pr) 4 · i-PrOH (99.9%), o-anisidine, and all commercially available aldehydes were purchased from Aldrich and used without further purification except the following: hydrocinnamaldehyde and heptaldehyde were distilled from CaCl 2 and valeraldehyde was distilled under inert atmosphere. 4-(3-Oxopropyl)benzoic acid methyl ester, [14] 6-oxohexanoic acid isopropyl ester, [15] 5-oxopentanoic acid methoxymethylamide, 6-oxohexanoic acid methoxymethylamide, [16] 2-tert-butyldiphenylsiloxyacetaldehyde, [17] and 4-tert-butyldimethylsiloxybutyraldehyde [18] were prepared according to literature procedures. Bis(4-methylpentyl)zinc and dioctylzinc were prepared via a B-Zn exchange according to literature precedence.…”