Prenylflavans from Tephrosia watsoniana

2H‐Chromenes Generated by an Iron(III) Complex‐Catalyzed Allylic Cyclization

“…As 4a and 4b were obtained in good yields, the total synthesis of a natural product, tephrowatsin B, was envisioned (Scheme ). Tephrowatsin B was isolated from Tephrosia watsoniana, a plant which is known for its insecticidal activities and was described as a racemic mixture 5. The synthesis started from the commercially available 2,4,6‐trimethoxybenzaldehyde 7 which was selectively monodemethylated using tribromoborane and the resulting phenol 8 was obtained in 45% yield and subsequently C ‐allylated at C‐3 by a two‐step procedure, implying an O ‐allylation followed by a thermal Claisen rearrangement.…”

Enantioselective Synthesis of Chromenes via a Palladium‐Catalyzed Asymmetric Redox‐Relay Heck Reaction

“…Chromene and chroman rings are key heterocycles present in a variety of natural occurring products and bio‐active molecules such as ( S )‐candenatenin E, hilgartene, BW683C, and tephrowatsin E (Figure ). Thus the development of efficient synthetic methods to access these motifs has received a tremendous amount of attention, and many strategies have been reported .…”

Flavans and proanthocyanidins

“…Tephrosia watsoniana leaf (Gomez et al, 1985) e 4',5, 7-lriOMe O(c) Xanthorrhea preissii resin (Birch & Salahuddin , 1964) l::l 4', 7-diOH-3'-OMe -6.9(m) Iryanthera elliptica wood (Braz Filho et al, 1980a) '" Dracaena draco resin (Camarda et al, 1983) l::l Zephy ranthes flava bulbs (Ghosal et al, 1985b) l::l... 7-0 H-3', 4'-methylenedioxy -14.2 Zephyranthes flava bulbs (Ghosal et al, 1985b) '1;:) "'l 3', 4'-diOH-5,7-diOMe 0 Iryanthera coriacea wood (Franca et al, 1974) <:> 2'-OH-7-0Me-4', 5'-m ethylenedioxy 0 l ry anthera juruensis wood (Franca et al, 1974) l::l Zephyr anthesflava bulb (Ghosal et al, 1985) ....…”

“…Dracaena dracoresin (Camarda et al, 1983) 2', 7-diOH-4', 5'-meth ylenedioxy-6, 8-diMe Iryanthera laevis wood (Braz Filho et al, 1980b) 2', 7-diOH-4', 5'-methylenedioxy-5, 8-diMe l ry anthera laevis wood (Braz Filho et al, 1980b) 2', 5-diOH-4', 5'-methylenedioxy-6, 8-diMe lryanthera laevis wood (Braz Filho et al, 1980b) (4) Prenylated 5,7 -diOMe-8-pr* -79.5(c) Tephrosia watsoniana leaf (Gomez et al, 1985) Tephrosia madrensis leaf (Gomez et al, 1983) 3',4', 7-triOH-2',5'-di-pr (kazinol A) -l1(c) Broussonetia papyrifera cortex (Ikuta et al, 1985) kazinol B (2.15) -20(c) Broussonetia papynf era cortex (Ikuta et al, 1985) nitenin (2.16) Tephrosia nitens leaf (Gornez et al, 1984) Tephrosia watsoniana leaf (Gomez et al, 1985) (5) O-Glycosides 5-0 H-7-0 Glc (koaburanin) -64.2(e) Enkianthus nudipes leaf (Ogawa et al, 1970) 7, 4'-diOMe-5-0 Glc (dichotosin) -34.5(m) Hoppea dichotoma root (Ghosal et al, 1985a) 4', 7-diOH-5-0Xyl…”