Sequential Norrish Type II Photoelimination and Intramolecular Aldol Cyclization of 1,2‐Diketones in Carbohydrate Systems: Stereoselective Synthesis of Cyclopentitols

Abstract

Öffnen und wieder schließen: Die Photoanregung von 2,3‐Diulosen I mit sichtbarem Licht löst eine ungewöhnliche sequenzielle Umlagerung aus: eine Norrish‐II‐Photoeliminierung unter Bildung der isolierbaren acyclischen Photoenol‐Zwischenstufe II, an die sich eine intramolekulare Enolexoaldolisierung anschließt. Die Kontraktion des Pyranoserings führt zu neuartigen Cyclopentitolen III. R=Acyl, Alkyl, Silyl.

Sequential Norrish Type II Photoelimination and Intramolecular Aldol Cyclization of α‐Diketones: Synthesis of Polyhydroxylated Cyclopentitols by Ring Contraction of Hexopyranose Carbohydrate Derivatives

“…4, 6,7, (18): Prepared from 11 (70 mg, 0.125 mmol) following the general procedure (Method B) using NaIO 4 (107 mg, 0.5 mmol) and RuO 2 ·x H 2 O (1.1 mg). The reaction mixture was stirred at room temperature in the dark for 1 h. The residue was purified by rapid silica gel column chromatography (hexanes/EtOAc 9:1) to give 18 (46 mg (0.6 mL), was placed in a resonance tube and irradiated with a daylight lamp at 30 8C for 2 h. The mixture was concentrated under reduced pressure and the residue was purified by silica gel column chromatography (hexanes/EtOAc 9:1), to give (2S,3aS,4S,5R,6S,6aR)-4,5,6-tris(benzyloxy)-6a-[(benzyloxy)methyl]-2-hy- 13 C NMR (100.6 MHz, CDCl 3 ): d = 20.6 (CH 3 ), 51.6 (CH), 71.8 (CH 2 ), 72.0 (CH 2 ), 72.6 (CH 2 ), 73.3 (CH 2 ), 74.3 (CH 2 ), 82.6 (CH), 85.0 (CH), 87.7 (C), 88.5 (CH), 99.2 (C), 127. , 135.9 (C), 137.5 (C), 137.6 (C), 137.8 (C), 208.3 ppm (C); IR (film) (19) (1.4 mL), was placed in a resonance tube and irradiated with a daylight lamp at room temperature for 3 h. The mixture was concentrated under reduced pressure and the residue purified by silica gel column chromatography (hexanes/EtOAc 9:1) to give (3aS,4S,5R,6S,6aR)-4,5,6-tris ( (1) (1 mL), was placed in a resonance tube and irradiated with a daylight lamp at 30 8C for 1 h. The mixture was concentrated under reduced pressure and the residue purified by silica gel column chromatography (hexanes/EtOAc 8:2) to give (3aS,4S,5R,6-S,6aR)-4,5,6-tris(benzyloxy)-6a-(acetyloxy)methyl-2-hydroxy-2-methylte- (27) (100) (100) (100)…”

“…The reaction was monitored by 1 H NMR spectroscopy, complete consumption of starting material was observed after 9 h. Then, the reaction mixture was heated at 60 8C for 5 h and concentrated under reduced pressure. The residue was solved in CH 2 Cl 2 (0.82 mL) cooled to 0 8C and acetylated by adding Ac 2 O (29 mL, 0.306 mmol) and DMAP (37 mg, 0.306 mmol) followed by stirring at room temperature for 2 h. The reaction mixture was concentrated under reduced pressure and the residue partially resolved by silica gel column chromatography (hexanes/EtOAc 8:2) to give (2R,3aS,5R,6S,6aR)-6a-[(tert-butyldiphenylsilyl)oxy]methyl-5,6-dimethoxy-2-methyl-3-oxohexahydro-2H-cyclopenta[b]furan-2-yl acetate (44) 13,H 7.27;found: C 66.11,H 7.58. 4,7,: Prepared from 33 (111 mg, 0.486 mmol) following the general procedure (Method A) using dimethyl sulfide (71 mL, 0.970 mmol).…”

“…The residue was purified by rapid silica gel column chromatography (hexanes/EtOAc 97:3) to give 70 (19 mg, 0.039 mmol, 69 %) as a yellow oil and the known lactone 73 [47] (2 mg, 0.005 mmol, 6 %). 85.4 (CH), 113.3 (C), 127.9 (4 CH), 129.9 (CH), 130.0 (CH), 132.5 (C), 132.6 (C), 135.5 (2 CH), 135.6 (2 CH), 192.2 (C), 197.7 ppm (C); 13…”

“…a colorless oil as a mixture of isomers(23.5 mg, 0.043 mmol, d.r., 1:0.9, 67 %): 1 H NMR(500 MHz, CDCl 3 ; complex spectrum, only clearly distinguished signals are reported): d = 1.35 (s, 3 H),1.42 (s, 3 H), 2.03 (s, 3 H), 2.09 (s, 3 H), 3.07 (d, J = 1.9 Hz, 1 H), 3.11 (d, J = 3.2 Hz, 1 H), 3.92 ppm (d, J = 5.4 Hz, 1 H);13 C NMR (100.6 MHz, C 6 D 6 ; complex spectrum, only clearly distinguished signals are reported): d = 20.8 (CH 3 ), 20.9 (CH 3 ),21.5 (CH 3 ), 22.5 (CH 3 ), 52.7 (CH), 54.9 (CH), 65.8 (CH 2 ), 65.9 (CH 2 ), 87.7 (CH), 87.9 (C), 88.7 (C), 99.3 (C), 100.0 (C), 170.3 (C), 170.4 (C), 206.6 (C), 210.3 ppm (C); IR (film): ñ = 3424, 2927, 1742 cm À1 ; MS (EI): m/z (%): 546 (< 1) [M + ], 503 (< 1); HRMS (EI): m/z calcd for C32 H 34 O 8 : 546.2254 [M + ]; found: 546.2273; elemental analysis calcd (%) for C 32 H 34 O 8 (546.61): C 70 31,. H 6.27; found: C 70.10, H 6.40.…”

“…The residue was purified by rapid silica gel column chromatography (hexanes/EtOAc 1:1) to give 21(38 mg, 0.072 mmol, 59 %) as a yellow oil. [a] D = + + 52 cm 3 g À1 dm À1 (c = 2.32 in CHCl 3 ); 1 H NMR (400 MHz, CDCl 3 ): d = 2.12 (s, 3 H), 3.34 (dd, J = 13.3, 5.0 Hz, 1 H), 3.51 (dd, J = 9.8, 7.2 Hz, 1 H), 3.55 (dd, J = 13.3, 2.4 Hz, 1 H), 3.77 (dd, J = 8.0, 7.4 Hz, 1 H), 4.08 (dd, J = 8.2, 7.4 Hz, 1 H), 4.43 (ddd, J = 9.7, 4.6, 2.1 Hz, 1 H), 4.50-4.82 (m, 6 H), 5.60 (d, J = 7.2 Hz, 1 H), 7.18-7.37 ppm (m, 15 H);13 C NMR (100.6 MHz, CDCl 3 ): d = 23.5 (CH 3 ), 51.7 (CH 2 ), 72.6 (CH), 74.0 (CH), 74.1 (CH 2 ), 74.3 (CH 2 ), 74.7 (CH 2 ), 77.7 (CH), 78.2 (CH), 80.2 (CH), 127.8-128.6 (15 CH), 136.7 (C), 137.7 (C), 137.9 (C), 197.2 (C), 199.8 ppm (C); IR (film): ñ = 2925, 2099, 1731, 1715 cm À1 ; MS (ESI + ): m/z (%): 584 (100) [M + +MeOH+Na]; HRMS (ESI + ): m/z calcd for C 31 H 35 N 3 NaO 7 : 584.2373 [M + +MeOH+Na]; found: 584.2372. All attempts at obtaining correct elemental analysis for this azide in two different analyzers failed.…”