22. Gibberellic acid. Part XXI. The stereochemistry of rings B, C, and D

The chemistry of the gibberellins

“…Reduction with hydrazine is more stereospecific, giving the 16p-methyl compound as the only isolable Hydrogenolysis and further catalytic reduction brings about the inversion of configuration at C-10.33 The cis-fused A/B ring junction in (18) leads to a difference in reactivity of the 3-hydroxyl group when the hydrogenolysis products and the corresponding gibberellin A, derivatives are compared, (vide infra). An X-ray analysis of the hydrogenolysis acid, 'hydrogeno-1 ' (14), revealed that it retained a P-proton at C-9. 34 The products of relactonization of the hydrogenolysis acids possess the same C-5 and C-9 stereochemistry as the parent gibberellic acid.…”

“…Catalytic hydrogenation of methyl gibberellate (1 1) (e.g. over 10 YO palladium on charcoal or with platinum in acetic acid) is accompanied by hydrogenolysis of the lactone On the one hand reduction affords gibberellin A, methyl ester (1 3) and the 16-epimeric tetrahydroderivatives (1 5) whilst on the other hand hydrogenolysis led to a series of di-and tetrahydro-acids (14), (16), (17). The acids, depending on the ease of access of the remaining double bond, could be further reduced to hexahydro-acids.…”

“…and chiroptical), and X-ray studies. [13][14][15][16][17] In the course of the subsequent chemical work there have been a number of X-ray studies on other gibberellins and their derivatives. A comparison has been carried outls between the methyl esters of the C,, gibberellin A,, (7) and the C,, gibberellin A, (5).…”

Stereochemical Aspects of Some Rearrangements of Gibberellic Acid

“…Chlorination of the methyl ester of gibberellin A 1 2 R = OH, gave 24 R = CH 2 Cl. 51 Bromination of methyl gibberellate was more complex. Simple bromination gave the rearrangement product 24 R = CH 2 Br.…”

General strategy for gibberellin synthesis: total syntheses of (.+-.)-gibberellin A1 and gibberellic acid

“…The introduction of a C(10) oxygen function with concomitant elaboration of the thermodynamically less stable cis-B/C ring fusion3b was achieved through the addition of the~ylborane'~ (ether, 0 "C, 3.5 h; Na2HP04, H202, 35 (23) An extensive range of alkyne, alkene, and alkane-derived organometallic reagents, in the presence or absence of amines and Lewis acids, was added to 14 and dihydrel4, but either enolization or no reaction was observed. ments to the isomeric acids were made through analogy with the 13-deoxy analogues9 and confirmed by I3C NMR spectra of the derived methyl esters 10 and 1l,l6 which indicated shielding by the ester function of C( 14) in the 6a-epimer and of C(15) in the 60-epimer.…”