Synthesis of 6-methoxy-2,2-dimethyl-2H-1-benzothiopyran and 6,7-dimethoxy-2,2-dimethyl-2H-1-benzothiopyran,sulfur analogues of precocene I and precocene II

Preparation of title compounds 5 , sulfur analogues of the natural insect antijuvenile hormones precocene I and II, is described. The synthetic pathway involves conversion of the appropriate thiophenol 2 into the corresponding thiochroman-4-one 4 followed by reduction and dehydration. The ¹³C nmr data for all the above products are also reported.     

Bentonitic earth catalyzed rearrangement of aryl 1,1-dimethylpropargyl ethers. Synthesis of 2,2-dimethyl-2H-1-benzopyrans

Mexican Bentonitic earth (Tonsil) catalyzed the Claisen rearrangement of aryl 1,1-dimethylpropargyl ethers under mild conditions to provide 2,2-dimethyl-2H-1-benzopyrans. The synthesis of encecalin 2f and desmethoxyencecalin 2i , two biologically active products among other natural products ( 2b, 2e ) was performed by this procedure.     

Construction of 6-amino-2,2-dimethyl-3,4,6-trisubstituted-2H-1-benzopyran library by solid phase synthesis

We report the solid-phase library construction of 2000 analogues of 6-amino-2,2-dimethyl-3,4,6-trisubstituted-2H-1-benzopyran. The polymer-bound hydroxyalkoxychromanes 5, produced by nucleophilic reactions with various alcohols on epoxides generated in situ, served as key intermediates for subsequent diversification. Further reactions on these hydroxyalkoxychromanes 5 with various electrophiles, such as alkyl halides and acid halides, produced the desired 6-amino-2,2-dimethyl-3,4,6-trisubstituted-2H-1-benzopyran analogues 9, 10, and 11. The progress of reactions could be monitored as solid-bound intermediates by ATR-FTIR or HR-MAS-NMR spectroscopy. The final compounds, obtained in good yields and high purity upon cleavage from the resins, were characterized by LC/MS, HRMS, (1)H NMR, and (13)C NMR spectroscopy.     

Oxidation reactions of 3,4,5-triamino-1,2,6-thiadiazine 1,1-dioxide. Preparation of 3,5-diamino-4H-1,2,6-thiadiazin-4-one 1,1-dioxide

Oxidation reactions of 3,4,5-triamino-1,2,6-thiadiazine 1,1-dioxidc with hydrogen peroxide and chromium trioxide are reported. 3, 5-Diamino-4H-1,2,G-thiadiazin-4-one 1,1-dioxide is synthesized by different methods.     

Fluorinated chromenes. III. Synthesis of 3-fluoro-2,2-dimethyl-2H-chromenes

The reaction of 2-fluoro-1,1-dimethoxy-3-methylbut-2-ene ( 3 ) with phenols in dry pyridine leads to 3-fluoro-2,2-dimethyl-2H-chromenes. 3-Fluoro analogues of the natural insect antijuvenile hormones Precocene I ( 1a ) and II ( 1b ) have been prepared by this method.     

A novel synthesis of precocenes. Efficient synthesis and regioselective O-alkylation of dihydroxy-2,2-dimethyl-4-chromanones

The reactions of trihydroxybenzenes 1a-c and 3-methylbut-2-enoic acid ( 2 ) in a zinc chloride/water/phosphoryl chloride system afford either the new trihydroxyphenylbutenone derivatives 3b,c or dihydroxy-2,2-dimethyl-4-chromanones 4a-c in good yields. Compounds 3b,c can be cyclized in high yields to 4b,c in 5% sodium hydroxide solution. Regioselective O-alkylation of 4a-c leads to 5a-f in good yields. O-Alkylation of 5a-f , followed by reduction and dehydration, results in the formation of precocene 3 ( 7d ) and its regioisomer 7a-c,e,f . Methylation of 4a-c gives 6g-i . Subsequent reduction and dehydration affords precocene 2 ( 7h ) and its regioisomers 7g,i .