3- propenyl pyrans

Bromination of a methyl group in a pyran-2-one is a useful first step to a number of derivatives, for example 4-methoxy-6-(l-propenyl)pyran-2-one (329) (74JOC3615). NBS monobrominates methyl groups only on the benzene ring of coumarins and nuclear bromination has not been observed (47CR937). 

Destannylative reactions. l-Trimethylstannyl-2,4-pentadiene reacts with aldehydes and ketones in a -y-selective manner, whereas conjugated dienes are generated from 3-(tributylstannyl)propenyl pyrans. ... 

Pyran-2-one, 4-methoxy-6-( 1 -propenyl)-synthesis, 3, 690 Pyran-2-one, 6-methyl-bromination, 3, 690 Pyran-2-one, 6-(2-methylpropenyl)-synthesis, 3, 796 Pyran-2-one, 3-methylthio-synthesis, 3, 796 Pyran-2-one, 3-nitro-6-phenyl-oxidation, 3, 681 Pyran-2-one, 6-phenyl-chlorination, 3, 679... 

Z)-4,4,5,5-tetramethyl-2-[3- 2-trimethylsilylethoxy)-2-propenyl -1,3,2-dioxaboroUme yield 45% (Z)-2-[3-(tetralnclr -2H-pyran-2-y/oxy)-2-propenyl]-4,4,5,5-tetramethyl-1,3,2-dioxaborolane yield 52%. 

Relatively few studies of the reactions of allylboron compounds and ketones have appeared. Ketones are less reactive than aldehydes, and as a result these reactions tend to be much slower and often less diastereoselectivc. The reaction of (Z)-4,4,5,5-tetramethyl-2-[3-(tctrahy-dro-2/A-pyran-2-yloxy)-2-propenyl]-1,.3,2-dioxaborolane and ethyl 2-oxopropanoate, for example, was conducted under 6 kbar pressure at 45 C for 80 hours to give a 9 1 mixture of syn-and antz-diastereomers of 1 in 85% yield49. 

Z)-2-Acetoxy-ethenyl]-l -methyl-2-(2-methyl-l-propenyl)- E15/1, 113 [5,6-H2 —2H-pyran +... 

Tetrahydro-4-methyl-2-(2-metliyl-l-propenyl)-2//-pyran (2) Typical Procedure67 ... 

The reaction course strongly depends on the solvent employed. In fact, when (Z)-6-nonen-2-ol (1) is cyclized in dimethyl sulfoxide, no migration of the double bond occurs and tetrahydro-2-methyl-b-ffis)- -propenyl]-2//-pyran (2) is obtained in quantitative yield. The cyclization proceeds with high 1,3-asymmetric induction and the major product has the 2,6-cis relationship. The larger substituents preferentially occupy the equatorial position, due to thermodynamic control of the reaction and equilibration of the chair conformers81. 

TV-Substituted 2-oxo-jV-(2-propenyl)-2//-pyran-6-carboxamides underwent spontaneous IMDA reaction under the conditions employed for their formation from TV-substituted 2-propenylamines and 2-oxo-2//-pyran-6-carbonyl chloride44. The products 19 were converted in almost quantitative yield on gentle heating to 2,4-disubstituted 2,3-dihydro-l//-isoindol-l-... 

Elenolide. 4-(l-Formyt-l-propenyl)-3,4-dihydro-2-oxo-2H-pyran- -carboxylic acid methyl ester. 

Hydroxy-6-propenyl-2-pyrone heated 3 hrs. at 100° with crotonoyl diloride in tetrachlorethane in the presence of TiCl4 3,4-dihydro-2-methyl-7-propenyl-2H,5H-pyrano[4,3-b]pyran-4,5-dione. Y 70%. K. Kato, Y. Hirata, and S. Yama-mura, Chem. Commun. 1969, 95. 

Isobutenyl methyl ketone. See Mesityl oxide 2-lsobutenyl-4-methyltetrahydropyran. See Tetrahydro-4-methyl-2-(2-methyl-1-propenyl)-2H-pyran... 

Methyl 2-methyl-2-propenoate, polymer with 2-methyl-2-propenoic acid, 1,2-ethanediyl ester. See Methyl methacrylate crosspolymer 4-Methyl-2-(2-methyl-1 -propenyl) tetrahydro-2H-pyran. See Tetrahydro-4-methyl-2-(2-methyl-1-propenyl)-2H-pyran... 

Terpinyl formate Terpinyl isobutyrate Terpinyl isovalerate Terpinyl propionate 4,5,6,7-Tetrahydro-3,6-dimethylbenzofuran Tetrahydrofurfuryl acetate Jetrahydrofurfuryl alcohol Tetrahydrofurfuryl butyrate Tetrahydrofurfuryl cinnamate Tetrahydrofurfuryl propionate Tetrahydrolinalool Tetrahydro-4-methyl-2-(2-methyl-1 -propenyl)-2H-pyran Tetrahydro-pseudo-ionone Tetramethyl ethylcyclohexenone 2,3,5,6-Tetramethylpyrazine... 

Figure 4. Electron ionization mass spectra [111 of three isomers (a) acetic acid 2-propenyl ester (b), tetrahydro-2H-pyran-2-one, and (c) 3-methyl-2-butenoic acid illustrating the variation in mass spectral pattern with change in structural features.

The effect of structural change on the mass spectral pattern is illustrated in Figure 4, which compares the 70 eV mass spectra of the three isomers acetic acid 2-propenyl ester, tetrahydro-2H-pyran-2-one and 3-methyl-2-butenoic acid. The spectra were taken from the NIST Mass Spectral Database (11). 

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