Rearrangement dienol-benzene

S)-norprotosinomenine (135). This was established (120) in feeding experiments with C. laurifolius DC. The proposed route is summarized in Scheme 34, where reduction of 136 to 141 was originally thought to occur, followed by a dienol-benzene rearrangement to 142. However, cyclization of 142 to isococculidine (36) is hard to visualize, although intermediate 143 was postulated. An alternative route (11a) involves reduction of the diphe-noquinone 144 to 145, followed by cyclization to 146 and further elaboration to 36. 

In a similar way, O-methylflavinantinol (59) rearranges under the action of boron trifluoride etherate to give, via the neospirinedienone 60, the iminium salt 61, whose catalytic reduction produces laurifonine (4) in excellent overall yield (55) (Scheme 15). Laurifonine (4) has also been obtained by TFA-promoted dienol-benzene rearrangement of 59 followed by reduction with sodium borohydride 24). 

A parallel biogenetic scheme has been suggested by Theuns et al. (24) for the formation of neodihydrothebaine (7) in Papaver bracteatum. In this case the route proceeds through the isomeric salutaridinol (103), which is derived by para-ortho coupling of reticuline (Scheme 29). It has been suggested that salutaridinol (103) (or thebaine) is the precursor of bractazonine (8), but in this case via a proerythrinadienone formed by aryl migration in the dienol-benzene rearrangement (24) (Scheme 30). 

In view of the similarity between the reaction mechanisms proposed for the dienone-phenol and the dienol-benzene rearrangements it is hardly surprising that the two groups of reactions exhibit similar trends. The dienol 29) [171] and derivatives with 2-methoxy [X73], 3-methyl [174,175], or ii-hydroxyl substituents [ 176] follow path A leading mainly to 4-methyl derivatives (31). 

Barton and Cohen (48) were the first to suggest the seminal idea that dienones could be intermediates in the biosynthesis of aporphine alkaloids from benzylisoquinolines, since such dienones could rearrange to the aporphine nucleus either through a dienone-phenol or a dienol-benzene rearrangement as shown in the scheme on the following page. 

The dienol-benzene rearrangement has been used to advantage to explain the structures of several abnormal aporphine alkaloids (49) from a biogenetic point of view, and has also allowed the first s3uithesis of the aporphine alkaloid isothebaine (L) (50). (+ )-Orientaline (XLVII) was oxidized by alkaline ferricyanide to give a mixture of two dienones (XLVIII) in 4% yield. One of the dienones was reduced with sodium borohydride to a mixture of two dienols XLIX which, without... 

Two studies have appeared dealing with the phenolic oxidative coupling of the dihydric benzylisoquinoline LI. In the first study, oxidation of LI with potassium ferricyanide yielded two dienones (LII), one of which was obtained crystalline. The crystalline material was reduced with sodium borohydride to two noncrystalline dienols (LIII) which underwent dienol-benzene rearrangement in anhydrous methan-olic hydrogen chloride to ( )-corydine (XXVI). Rearrangement of the... 

The dienone-phenol rearrangement is widely employed for the synthesis of many polycyclic structures, the formation of which demands an expansion of one of the cycles. Thus, the aporphine-type plant alkaloids 307-310 can be obtained via the dienone-phenol rearrangement of orientalinone 305 and dienol-benzene rearrangement of orientaUnol 306 (equation 148). 

Analogous rearrangements were reported for similar systems such as proaporphines , the alkaloids of Croton sparsiflorusMorong and cannabinoids . The dienone-phenol and dienol-benzene rearrangements were studied in the eupodienone-1 series (a constituent of Eupomatia laurina R. Br.). These compounds 311 were transformed under a variety of acidic conditions into dibenzocyclooctene derivatives (equation 149). 

The mechanism of the dienol-benzene rearrangement has yet to be elucidated the configurations of C-10 and C-13 of orientalinol-I (see 70) are unknown. In order to see if the product (72) of an allylic rearrangement could be interposed between orientalinol-I and isothebaine, H-labelled (72) was fed as a mixture of dienols to P. orientale. No incorporation was found, but the significance of this is not clear as the configuration at the spiro centre is uncertain. 

The reduction with borohydride and the acid-catalyzed dienone-phenol/dienol-benzene rearrangements leave the center of chirality at C-6a intact. Consequently, the absolute configuration of this center can be intercorrelated with that of the benzylisoquinoline, proaporphine, and aporphine alkaloids (Schemes 1, 2, and 20). 

The biosynthesis of aporphine alkaloids takes the course—laudanoso-line, norlaudanosoline, reticuline, or orientaline—by means of phenolic oxidation via the cyclohexadienone proaporphine (27, 28, 39, 40, 47, 49, 65, 66, 68, 69,147,148,150, 229, 231, 240, 250, 275, 349, 445, 451, 512) after dienone-phenol or dienol-benzene rearrangement, as described in more detail in the preceding section. The foregoing results, considered as a whole (39,49), provide good evidence that isothebaine is biosynthesized in P. orientale along the following pathway ... 

Other references related to the dienol-benzene rearrangement are cited in the literature. ... 

This reaction is related to the Dienol-Benzene Rearrangement. 

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