Carotenoids and related compounds. Part 40. Synthesis of trikentriorhodin and other β-diketones

Abstract

Three routes to polyene 0-diketones are described.Condensation of 8'-apo-P-carotenal (4) and of 8,8 '-diapo-carotene-8,8'-dial (6) with butylamine in the presence of tri-isobutyl borate gave the Schiff's bases (5) and ( 7 ) respectively. These reacted with the boric oxide complex of acetylacetone t o give the polyene B-diketones (8) and ( 9).Reaction of the di-lithium salt of 3-methylpent-I -en-4-yn-3-01 (32) with pivalic anhydride (1 1 ) yielded the acetylenic ketone (34)' which on hydration furnished the P-diketone (36). This was converted into the Wittig salt (39) which condensed with the trienedial (44) t o give the polyene pdiketones ( 45) and ( 46).Polyene carboxylic esters were found t o condense with methyl ketones, in the presence of lithamide, t o give P-diketones in high yield. Thus methyl 8'-apo-~-carotenoate (59)' for which a synthesis from ( 44) is reported, condensed with the trimethylsilyl derivative of the optically active hydroxy-ketone (64) t o give, after hydrolysis of the protecting group, trikentriorhodin (1). Comparison of the c.d. properties of the synthetic compound, w i t h those reported for the natural pigment, indicate that the latter has the 3S, 5R configuration.

Hybrid Synthetic and Computational Study of an Optimized, Solvent-Free Approach to Curcuminoids

“…The same color change pattern is also observed when imine is synthesized independently. The possibility of converting imines to the corresponding curcuminoids upon reaction with complex 5 was independently confirmed by Chopra 14 for solvent-based conditions and by us for solvent-free conditions. Since the imine (or iminium ion) formation can only occur with primary (or secondary) amines, in retrospect, it is not surprising that tertiary amines have been reported to be ineffective catalysts for curcuminoid formation.…”

“…Chopra et al speculated that the actual intermediate is a Schiff base formed by the substituted benzaldehyde and amine in the presence of a borate ester. 14 Reaction of 8′-apo-β-carotenal 6 was carried out using tri(isobutyl) borate and n -butyl amine after the formation of complex 5 and did not result in the condensation of aldehyde ( Scheme 3 ) but provided several Schiff base intermediates, e.g., compound 7 . 14 Isolated compounds upon combining with the boric oxide complex of acetylacetone 5 in ethyl acetate under reflux for 14 h produced polyene diketones after treatment with HCl and crystallization from ethyl acetate ( Scheme 3 ).…”

“… 14 Reaction of 8′-apo-β-carotenal 6 was carried out using tri(isobutyl) borate and n -butyl amine after the formation of complex 5 and did not result in the condensation of aldehyde ( Scheme 3 ) but provided several Schiff base intermediates, e.g., compound 7 . 14 Isolated compounds upon combining with the boric oxide complex of acetylacetone 5 in ethyl acetate under reflux for 14 h produced polyene diketones after treatment with HCl and crystallization from ethyl acetate ( Scheme 3 ). 14 Although speculated, similar imine compounds, e.g., 7 , were neither observed during the TLC monitoring of the reactions nor isolated for the synthesis of curcumin itself.…”

“… 14 Isolated compounds upon combining with the boric oxide complex of acetylacetone 5 in ethyl acetate under reflux for 14 h produced polyene diketones after treatment with HCl and crystallization from ethyl acetate ( Scheme 3 ). 14 Although speculated, similar imine compounds, e.g., 7 , were neither observed during the TLC monitoring of the reactions nor isolated for the synthesis of curcumin itself.…”

Cyanation of α-Ketoalkynes Catalyzed by Nickel in Water

“…Compounds 5 , 6 , 8 , 9 , 10 , and 11 were prepared by this method. Their spectral (IR, 1 H NMR, 13 C NMR) and elemental analyses were in accord with those reported.…”