Gibberellin ketone

Methylenation. The species obtained from the reaction of TiCl4 with zinc in < II iBr, and THF is the reagent of choice for methylenation of the gibberellin ketones I and 2, which undergo marked epimeri/ation at the adjacent chiral center on... 

Pioneering work on the desulphonylation of jS-ketosulphones was carried out by Corey and Chaykovsky - . This reaction was part of a sequence which could be used in the synthesis of ketones, as shown in equation (53). The main thrust of this work was in the use of sulphoxides, but Corey did stress the merits of both sulphones and sulphonamides for different applications of this type of reaction. The method soon found application by Stetter and Hesse for the synthesis of 3-methyl-2,4-dioxa-adamantane , and by House and Larson in an ingenious synthesis of intermediates directed towards the gibberellin skeleton, and also for more standard applications . Other applications of the method have also been madealthough it does suffer from certain limitations in that further alkylation of an a-alkyl- -ketosulphone is a very sluggish, inefficient process. Kurth and O Brien have proposed an alternative, one-pot sequence of reactions (equation 54), carried out at — 78 to — 50°, with yields better than 50%. The major difference between the two routes is that the one-pot process uses the desulphonylation step to generate the enolate anion, whereas in the Corey-House procedure, the desulphonylation with aluminium amalgam is a separate, non-productive step. 

Rearrangement of gibberellin Ax (IV) to the ketone (V) and oxidation of the latter gave a diketone (VI) which, on dehydrogenation gave 1,7-dimethyl-fluoren-2-ol (VII) whose structure was established by synthesis (13). 

Figure 15. Ring C ketones obtained from gibberellin Alt aUogibberic acid, and...

The diazo ketone methodology has provided a general route to gibberellins. Thus treatment of the diazo ketone 1, obtained from 1,7-dimethoxynaphthalene, with TFA resulted in the tricyclic dienedione 2, which was converted in a few steps to 3, which contains the B, C, and D rings of gibberellic acid (4).2... 

A total synthesis of ( )-royleanone from 5,7,8-trimethoxy-l-tetralone (123) has been described.129 The tetralone was converted into the tricyclic ketone (124), which was in turn converted into 11,12,14-trimethoxypodocarpatriene (125). Demethyla-tion and oxidation afforded the quinone (126 R = H) which was alkylated to give royleanone (126 R = Pr ). Synthetic studies in the resin acid series have led130 to the preparation of the dicarboxylic acid (127) with a cis a/b ring junction. The preparation of some tetracyclic ketones as intermediates for gibberellin synthesis has been described.131 132 The key reaction involves photolysis of a diazoketone (128) to afford the tetracyclic system (129). In a synthesis of phyllocladene from abietic acid... 

This reaction provided a key step in a stereocontrollcd total synthesis of r/Z-gibberellin A, 4 (3). Thusreactionoftheenone(l) with cxcessdiethylaluminumcyanidein methylene chloride at room temperature gave the C/D cij-cyano ketone (2) in 87% yield. Note... 

Irradiation of the a -unsaturated ketone derived by manganese dioxide oxidation of methyl gibberellate, affords, in the solid state, a dimer in which addition of the unsaturated ketone across the terminal methylene group has occurred. Photolysis in solution leads to addition of the solvent to the unsaturated ketone. Some interest has centred on the partial synthesis of gibberellin Ajg (105), whose total synthesis was reported earlier. Details of the conversion of gibberellin A g into some 5-lactones related to gibberellin A15, and on the partial synthesis of gibberellin Ajg nor-ketone from 7-hydroxykaurenolide, reported... 

The unsaturated ketone (70) is a catabolite of gibberellin A29. It has been prepared107 from gibberellic acid. The 2-position of gibberellins is metabolically reactive and consequently the biological activity of a number of 2-substituted... 

The procedure was used successfully in the synthesis of gibberellin C from the dienone group (7).4 The ketone group at C8 was protected by ketalization, carboxylation was conducted by the Robinson-Cornforth method, the resulting acid esterified with diazomethane, and finally the diketo diester (8) was obtained after... 

A partial synthesis of gibberellin Ajj nor-ketone from 7-hydroxykaurenolide has been described. The key stage in this synthesis is the activation of the C-20 methyl group by photolysis of a C-19 amide (173). 

The alternative fate, i.e. other than elimination of the 1,4-biradical formed by a Norrish Type II process, is the formation of cyclobutanols. Such is the outcome of the irradiation of the gibberellin derivative (64a) which yields the cyclobutanol (65). Treatment of this derivative with a tritium or deuterium donor affords the labelled derivative (64b).Azetidinols (66) are formed on irradiation of the ketones (67) in ethereal solution. The azetidinols (66) arise by way of the Norrish... 

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