Highly Brominated Norbornanes by Photobromination as Precursors for the Convenient Synthesis of 2,3,5,6-Tetrabromo- and 2,3,5,6-Tetramethoxy-substituted Norbornadienes

Abstract

H i g h l y b r o m i n a t e d N o r b o r n a n e s b y P h o t o b r o m i n a t i o nAbstract: An efficient synthesis is described for hexabromonorbornane by photobromination of norbornadiene. Double dehydrobromination of the hexabromide by t-BuOK affords in high yield 2,3,5,6-tetrabromonorbornadiene, its copper-assisted treatment with sodium methoxide leads to the 2,3,5,6-tetramethoxy derivative. The tetrabromide constitutes a valuable precursor for the preparation of functionalized tetrasubstituted norbornadienes.When norbornadiene is converted photochemically to the higher-energy quadricyclane, the stored energy may be released by reverting catalytically the strained quadricyclane to its norbornadiene. Since norbornadiene itself does not undergo efficient valence isomerization upon direct and/or sensitized irradiation, norbornadienes with appropriate chromophores have been synthesized and their photoisomerization examined. 1 In this context, tetrasubstituted norbornadienes have attracted considerable attention because their quadricyclanes may serve as potential solar-energy storage cells, but a convenient preparation of such norbornadienes is still lacking. 2 In particular, the 2,3,5,6-tetrasubstituted norbornadienes should be of interest, but their preparation has been to date quite difficult. In addition, substituted norbornadienes have served as key intermediates in the synthesis of natural products such as the prostaglandin endoperoxides PGH 2 and PGG 2 , 3 cis-trikentrin, 4 and B-santalol. 5Most literature syntheses of 2,3,5,6-tetrasubstituted norbornadienes rely on the Diels-Alder reaction between cyclopentadienes and highly activated acetylenes. Unactivated acetylenes are poor dienophiles, which limits the type of norbornadienes accessible by this method to derivatives with electron-withdrawing groups.Recently, we have succeeded in the preparation of 2,3,5,6-tetrabromonorbornane 3 by the selective bromination of norbornadiene 1 and we have developed a synthetic method for dibromonorbornadienes by dehydrobromination of the tetrabromide 3. 6 It was our intention to employ the exhaustive photobromination of norbornadiene to obtain still higher brominated norbornanes and norbornadienes. Presently, we report an effective and convenient procedure for the synthesis of 2,3,5,6-tetrabromonorbornadiene and demonstrate its value as precursor to the corresponding tetramethoxy-substituted derivative.The bromination of norbornadiene at the reflux temperature of CCl 4 afforded the two diastereomeric 3,5-dibromonortricyclanes 2 and the three diastereomeric 2,3,5,6-tetrabromonorbornanes 3, which were readily separated by fractional distillation in 40% and 54% yields (Scheme). 6 The subsequent photobrominations were performed in CCl 4 by irradiation with a projector lamp (250 W, visible light) in an immersion photochemical apparatus. 7The photobromination of the diastereomeric mixture of 3,5-dibromonortricyclane 2 with one or two equivalents of bromine at room temperature in CCl 4 resulted in a complex reaction mixtu...

Cycloaddition Reactions of Benzonorbornadiene and Homonorbornadiene: New Isoxazoline and Pyridazine Derivatives

“…). Cycloadditions to the double bond of the compounds such as norbornadiene derivatives were occurred form exo faces because of electron density . The electron density of isolated double bond belongs to benzonorbornadiene ( 4 ), and data (NMR and HRMS) of adducts 7a – d are consistent with the proposed structures.…”

“…Benzonorbornadiene ( 4 ) and homonorbornadiene ( 5 ) are norbornadiene derivatives and can be rearranged with reagents such as bromine because of their strained structure . Norbornadiene derivatives including nitrogen–oxygen atoms and their rearrangement products may be important.…”

Journey Describing Applications of Oxone in Synthetic Chemistry

“…Previous literature showed that a good number of methods are available for preparation of the p -peroxyquinols and that these methods included the use of oxygen and H 2 O 2 . − However, despite their efficiency, these methods have not yet been applied extensively. Treatment of 3,4,5-trimethylphenol ( 120 ) with Oxone in a basic medium afforded p -peroxyquinol 131 in 93% yield (Scheme ).…”

1,2-Dihaloalkenes in Metal-Catalyzed Reactions

“…In their synthesis of macamides, Kelley and co-workers used this strategy to prepare diene 103 from (E/Z)-1,2-dibromoethene (8b) by reaction with organoaluminum reagent 102 (Scheme 29). 44 In this case, the remaining bromide was functionalized through lithiation, followed by nucleophilic attack on glutaric anhydride (104) to provide macamide precursor 105.…”

“…Cakmak and co-workers obtained 2,3,5,6-tetramethoxynorbornadiene (207) as the sole product when they performed the Cu-assisted C-O bond formation between 2,3,5,6-tetrabromonorbornadiene (206) and sodium methoxide (Scheme 61). 104 Zhou and co-workers took advantage of microwave irradiation to perform a similar reaction and transform 2,3-di-halo-1,4-naphthoquinones (84) into 2,3-dihydroxy-1,4naphthoquinone (209), using aqueous potassium hydroxide as the nucleophile and with CuCl 2 /proline lithium salt (208) as the catalyst (Scheme 62). 105…”