2H-PYRAN-2-ONE, 5,6-DIHYDRO

Dihydro-2H-pyran-2-ones (e. g., 4-195) are valuable intermediates in the synthesis of several natural products [67]. Hattori, Miyano and coworkers [68] have recently shown that these compounds can be easily obtained in high yield by a Pd2+-catalyzed [2+2] cycloaddition of ct, 3-unsaturated aldehydes 4-192 with ketene 4-193, followed by an allylic rearrangement of the intermediate 4-194 (Scheme 4.42). In this reaction the Pd2+-compound acts as a mild Lewis acid. a,(3-unsaturated ketones can also be used, but the yields are below 20%. 

Complementary to the hetero-Pauson-Khand reaction (see Section 2.2.6), [2 + 2] cydoaddition of ketenes and aldehydes provides rapid access to P-lactones from relatively simple starting materials. Cationic [Pd(dppb)(CH3CN)2]Bp4 was selected as the optimal catalyst (Scheme 2.64) (122,123]. A tandem allylic rearrangement/ring expansion sequence was also developed that provides elaboration of P-lactones to 3,6-dihydro-2H-pyran-2-ones in a one-pot process (Scheme 2.65) [123]. 

The rhodium-catalyzed asymmetric conjugate addition is applicable to a,yS-unsaturated esters (Scheme 3.8). Hayashi reported [20] that the reachon of 5,6-dihydro-2H-pyran-2-one 19a with phenylboronic acid gave a 94% yield of phenylated lactone (S)-20am with 98% enanhomeric excess. For the linear enoates, organoboronic acids did not give... 

The other factor that may determine the type of cell death is the chemical structure of inducing agents [14]. We have recently found that u,(>-unsaluraled ketones such as 4,4-dimethyl-2-cyclopenten-l-one, a-methy-lene-y-butyrolactone, 5,6-dihydro-2H-pyran-2-one [15], codeinone [16], and morphinone [17] and a-hydroxylketones such as 3,3,3-trifluoro-2-hydroxy-1-phenyl-1-propanone induced caspase-independent cell death [18], induced vacuolization or autophagosome formation engulfing organelles, but without induction of apoptosis markers. 

A new class of bicyclic oxalactam, 8-oxa-6-azabicyclo[3.2.1]octan-7-one 61 was synthesized by intramolecular cyclization of 3,4-dihydro-2H-pyran- 2-carboxamide 62 using p-toluenesulfonic acid as a catalyst in an equivalent mixture of DMF and benzene at 100 °C for 4 hours57, S8. Corresponding conversion of 3-cyclohexane carboxamide 63 to bicyclic lactam 64 has never been accomplished54. ... 

To a stirred solution of dry N,N-diisopropylamine (1.1 ml, 7.85 mmol) in THF (10 ml) cooled to 0°C was added nBuLi (2.5 M in hexanes, 3.14 ml, 7.85 mmol) over several min. After the solution was stirred for 10 min following the addition, the reaction mixture was cooled to -78°C, and an additional 1 ml of THF was added. The acetic acid (+)-6-ethyl-5-methyl-2-(l-methyl-l-hydroxy-2-buten)-yl-3,6-dihydro-2H-pyran ester (1.65 g, 6.54 mmol) in THF (7 ml) was slowly added over a 40 min-period at -78°- (-70)°C. After the reaction was stirred for 5 min, TBSCI (1.18 g) in THF-HMPA (1 1,6 ml) was added in one portion. The cooling bath was then removed, and the reaction mixture was allowed to warm to 0°C and stirred for 1 h, then at room temperature for an additional 1 h, and finally 1.5 h at 65°C. The yellow solution was cooled to room temperature and diluted with THF (60 ml), then treated with a 10% HCI aqueous solution (16 ml). The reaction mixture was stirred at room temperature for 3 h The solvent was evaporated and the residue diluted with Et20 and treated with a 1.0 N KOH aqueous solution the organic phase was discarded, and the aqueous solution was washed with Et20. The basic solution was acidified with 10% HCI and the product isolated by ether extraction. This afforded 1.0 g (61%) of a 12 1 mixture of (+)-6-ethyl-5-methyl-2-(3-methyl-hex-4-enoic acid)-3,6-dihydro-2H-pyran as a colorless oil. This mixture was carried through the next reaction without further purification. 

A process for preparing a tautomeric mixture of the product of Step 3, (R)-3-hexyl-5,6-dihydro-4-hydroxy-6-undecyl-2H-pyran-2-one, (I), and (R)-5,6-dihydro-6-undecyl-2H-pyran-2,4(3H)-dione, (II), and (2), respectively, is described (3). 

Full experimental details have been published of the syntheses of kasugamycin (272, R = C(NH)C02H) from 3,4-dihydro-6-methyl-2H-pyran-2-one (271) and of methyl a-DL-mycaminoside (274), a-DL-oleandroside (275), a-DL-cy-maroside (276), a-DL-tyveloside (277), and a-DL-chromoside C(278) from 3,4-dihydro-2-ethoxy-6-methyl-2H-pyran (273). The schemes of these syntheses have been presented. ... 

However, when 36 was heated with a-amino heterocycles or with cyclic 1,3-dicarbonyl or potential 1,3-dicarbonyl compounds, 3-heteroarylp)rr-azol derivatives were obtained. In this manner 36 afforded, when heated with 2-aminopyridine and 3-amino-lH-pyrazol in acetic acid under reflux for 2 h and 5 h, respectively, 3-(5-ethoxy-l-phenyl-lH-pyrazol-3-yl)-4H-pyrido[l,2-fl]pyrimid-4-one (38) and 6-(5-ethoxy-l-phenyl-lH-p5rrazol-3-yl)pyrazolo[l,5-fl]pyrimid-7(lH)-one (39) in 70% and 77% 5deld, respectively. Similarly, 36 afforded with cyclicjS-dicarbonyl compounds, such as 4-hydroxy-6-methyl-2H-pyran-2-one and 5,5-dimethylcyclohexane-l,3-dione by heating in acetic acid for 4 h and 8 h, respectively, the corresponding 3-(5-ethoxy-l-phenyl-lH-pyrazol-3-yl)-7-methyl-2H,5H-pyrano[4,3- 7]pyran-2,5-dione (40) and 3-(5-ethoxy-l-phenyl-IH-pyrazol-3-yl)-7,7-dimethyl-7,8-dihydro-2H-chromene-2,5-dione (41) in 26% and 82% yield, respectively (Scheme 15). 

Shao, L., T. Seki, H. Kawano, and M. Saburi Asymmetric Hydrogenation of Methyl 3,5-Dioxohexanoate Catalysed by Ruthenium-binap Complex A Short Step Asymmetric Synthesis of Dihydro-6-methyl-2H-pyran-2-one. Tetrahedron Letters, 32, 7699 (1991). 

Metab. of C. piceae. [ag +23.8 (e, 0.34 in CHCI3). 4-Deoxy, 3,4-didehydro [154878-77-0]. 5,6-Dihydro-6-nonyl-2H-pyran-2-one, 2- Tetradecen-5-olide... 

P-d-Glucopyranosyloxy) -5,6-dihydro-4,6-dimethyl-2H-pyran-2-one. 4-P-d-Glucopyranosyloxy-3-methyl-2-hexen-5-olide... 

Preparation of Racemic 6,8-Dioxabicyclo[3.2.1]octan-7-one. To an aqueous solution of sodium 3,4-dihydro-2H-pyran -2-carboxylate (50 g) was added 6N hydrochloric acid (64 ml) in a few minutes keeping the temperature below lO C with external ice-cooling. After the addition of a sufficient amount of sodium chloride to saturate the solution, it was extracted several times with diethyl ether. The ether extract was washed three times with a saturated sodium chloride aqueous solution and dried over anhydrous sodium sulfate. The solvent was removed under reduced pressure and the residue was distilled. Yield 78% bp 68-70 C (4 mmHg) (lit.[9], bp 62-64 C (3 mmHg)). The monomer was dried over calcium hydride and fractionally distilled just before use. 

Preparation of (+)-(1R,5R)-6,8-Dioxabicyclo[3.2.1]-octan-7-one. An aqueous solution of sodium 3,4-dihydro-2H-pyran-2-carboxylate (25 g) was slightly acidified with 6N-hydrochloric acid, and the liberated carboxylic acid was extracted several times with diethyl ether. The ether extract was then added to an ice-cooled diethyl ether solution of dehydroabietylamine (46 g) which had been purified by repeated recrystallization of its acetate. Immediately after the addition, a white mass was formed. After being allowed to stand for half an hour, it was separated and re-... 

Sumitomo and coworkers prepared 6,8-dioxabicyclo[3.2.l]octan-7-one (37) and 6-aza-8-oxabicyclo[3.2.lJoctan-7-one (36) from 3,4-dihydro-2H-pyran-2-carbaldehyde (acrolein dimer), and polymerized these monomers by ring-opening methods (Fig. 15). The lactam (36) was polymerized to a high molecular weight polyamide (39). 

Propionic acid, 2-iodo-3-nitro-, ethyl ester [Propanoic acid, 2-iodo-3-mtro-, ethyl ester], 65 2//-Pyran, 3,4-dihydro-, 51 2//-PYR AN-2-ONE, 49 2H Pyran 2-one, 5 bromo 5,6-dihydro, 50 27/-PYRAN-2-ONE, 5,6 DIHYDRO-, 49 PYRIDINE, 2,3,4,5 TETRAHYDRO, 118 Pyridines, -substituted, 34 a Pyrone-6-carboxyhc acid [2H Pyran-6-Larboxyhc acid 2-oxo ], 51 Pyrroles, 34... 

Bromo-2(H)-pyran-2-one 2H-Pyran-2-one, 3-bromo- (8,9) (19978-32-6) 3-Bromo-5,6-dihydro-2(H)-pyran-2-one 2H-Pyran-2-one, 3-bromo-5,6-dihydro-(11) (104184-64-7)... 

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