H-Pyran-4-one

Naphtho[2,l -h]pyran-1 -one, 2,3-dihydro-dehydrogenation, 3, 724 halogenation, 3, 731 Naphthopyranones synthesis, 3, 805 Naphthopyran-2-ones, dihydrosynthesis, 3, 802 Naphtho[l, 2-h]pyran-2-ones synthesis, 3, 802 Naphtho[2,1 -h]pyran-3-ones synthesis, 3, 803, 856 Naphtho[2,1 -c]pyran-4-ones synthesis, 3, 831 Naphtho[2,3-c]pyran-l-ones synthesis, 3, 831 Naphthopyrans H NMR, 3, 580 IR spectra, 3, 594 synthesis, 3, 743, 748, 750, 763 UV spectra, 3, 598 Naphthopyrans, dihydrosynthesis, 3, 778, 783 Naphtho[l,2-h]pyran-4-thione, styryl-properties, 3, 708... 

An Improved Preparation of 3-Bromo-2(H)-pyran-2-one An Ambiphilic Diene for Diels-Alder Cycloadditions. 

AN IMPROVED PREPARATION OF 3-BROMO-2(H)-PYRAN-2-ONE AN AMBIPHILIC DIENE FOR DIELS-ALDER CYCLOADDITIONS (2H-Pyran-2-one, 3-bromo-)... 

A. 3-Bromo-5,6-dihydro-2(H)-pyran-2-one. A 1-L, three-necked, round-bottomed flask, equipped with a magnetic stirring bar, a pressure-equalizing addition funnel, a drying tube that contains sodium hydroxide pellets, and a thermometer, is charged with 10.15 g (0.103 mol) of 5,6-dihydro-2(H)-pyran-2-one (Note 1) and 350... 

TLC analysis was carried out on precoated plastic silica gel plates (with fluorescent indicator) using diethyl ether as eluant. With this eluant, the R of starting material is 0.50 and the Ri of 3,4-dibromo-3,4,5,6-tetrahydro-2(H)-pyran-2-one is 0.83. In addition to these two spots, a third spot, R = 0.55, corresponding to 3-bromo-5,6-dihydro-2(H)-pyran-2-one was detected. TLC analysis is not always reliable and it is better to analyze a small aliquot by NMR. 

The final series of five procedures presents optimized preparations of a variety of useful organic compounds. The first procedure in this group describes the preparation of 3-BROMO-2(H)-PYRAN-2-ONE, a heterodiene useful for (4+2] cycloaddition reactions. An optimized large scale preparation of 1,3,5-CYCLOOCTATRIENE, another diene useful for [4+2] cycloaddition, is detailed from the readily available 1,5-cyclooctadiene. Previously, the availability of this material has depended on the commercial availability of cyclooctatetraene at reasonable cost. A simple large scale procedure for the preparation of 3-PYRROLINE is then presented via initial alkylation of hexamethylenetetramine with (Z)-1,4-dichloro-2-butene. This material serves as an intermediate for the preparation of 2,5-disubstituted pyrroles and pyrrolidines via heteroatom-directed metalation and alkylation of suitable derivatives. The preparation of extremely acid- and base-sensitive materials by use of the retro Diels-Alder reaction is illustrated in the preparation of 2-CYCLOHEXENE-1.4-DIONE, a useful reactive dienophile and substrate for photochemical [2+2] cycloadditions. Functionalized ferrocene derivatives... 

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