Asymmetric Syntheses of the Flavonoid Diels–Alder Natural Products Sanggenons C and O

Abstract

Metal-catalyzed, double Claisen rearrangement of a bis-allyloxyflavone has been utilized to enable a concise synthesis of the hydrobenzofuro[3,2-b]chromenone core structure of the natural products sanggenon A and sanggenol F. In addition, catalytic, enantioselective [4+2] cycloadditions of 2′-hydroxychalcones have been accomplished using B(OPh)3/BINOL complexes. Asymmetric syntheses of the flavonoid Diels–Alder natural products sanggenons C and O have been achieved employing a stereodivergent reaction of a racemic mixture (stereodivergent RRM) involving [4+2] cycloaddition.

Synthesis, Characterization, Cytotoxic Activity, and Metabolic Studies of Ruthenium(II) Polypyridyl Complexes Containing Flavonoid Ligands

“…[38][39][40][41] Therefore, in order to Therefore, the synthesis of [Ru(DIP)2(mor)](OTf) involved an additional protection step shown in Scheme 1. Following a similar procedure to Qi et al, 42 the selective protection at the 2', 4', 3 and 7 positions with trimethylsilyl (TMS) protecting group was achieved. The protection step was performed in the presence of triethylamine and TMS-Br in THF and, following an aqueous workup, the protected morin was used in the complexation step without any further purification.…”

Asymmetric Synthesis of Dihydronaphthalene‐1,4‐Diones via Carbene‐Catalyzed Stereodivergent Reaction

“…Although the yield is 50% theoretically, the technique of divergent RRM is advantageous in providing diversified products and shortening the synthetic routes . Selected applications of this technique can be found in the total synthesis of (−)‐cyanthiwigin G/(+)‐cyathin A 3 , rotigotine/( S )‐8‐OH‐DPAT, (+)‐erogorgiaene/(−)‐colombiasin A,– and sanggenon C/sanggenon O, etc. In all these cases, the technique of divergent RRM proved to be the best choices in making the above structurally related pairs of natural products.…”

Recent topics of the stereodivergent synthesis of natural products

“…Porco and co-workers tried the total synthesis of sanggenons C (15a) and O (15b) by employing stereodivergent reaction of a racemic mixture. 18,20 First, double Claisen rearrangement of 16 with rare earth metal triflates was examined and Yb(OTf)3 was found to give the desired double rearranged product 17 in 72% yield (Scheme 5). After protection of 17 with TBSOTf/Et3N, cross-metathesis of the resulting diene with isobutene by using second generation Grubbs catalyst afforded prenylated product 18 in 92% yield in two steps.…”