Pterocarpans synthesis

Benzofurobenzopyrans, 4, 995-1000 6H-Benzofuro[3,2-c][l]benzopyrans, 6a,l la-dihydro-— see Pterocarpans Benzofurofurans mass spectrometry, 4, 585 Benzofuro[2,3-d]pyridazines synthesis, 4, 985... 

The lithiation of phenols protected as acetals—methoxymethyl acetals like 140 in particular—is especially valuable the second oxygen supplies a powerful coordination component to their directing effect (Scheme 69) The regioselective lithiation of 141 was used in the synthesis of the pterocarpans 4 -deoxycabenegrins A-I. 

Kiss, L. et al., Chiroptical properties and synthesis of enantiopure cis and trans pterocarpan skeleton. Chirality, 15, 558, 2003. 

Welle, R. and Grisebach, H., Induction of phytoalexin synthesis in soybean enzymatic cyclization of prenylated pterocarpans to glyceollin isomers. Arch. Biochem. Biophys., 263, 191, 1988. 

The first synthesis of pterocarpan was accomplished. by Suginome and Iwadare (60BCJ567). 2 -Hydroxyisoflavone, prepared from 2,2 -dihydroxydeoxybenzoin with ethyl formate and sodium, was reduced either with sodium borohydride or LAH to yield a mixture of stereoisomeric 2 -hydroxyisoflavan-4-ols. Treatment of this mixture with acid under mild conditions gives pterocarpan (Scheme 51). Racemic pterocarpin has also been prepared by this method (67ABC1490). 

Another synthesis of pterocarpans starts from the coumestan system. LAH treatment results in reductive cleavage of the a-pyrone ring (Scheme 52). Benzofuran derivative (242) is thermally cyclized to (243) (64JCS4212 see also 78IJC(B)372), which may also be formed... 

A very interesting and promising synthesis of pterocarpans (76CC500) involves Heck arylation of a 2-chromene (Scheme 53). The requisite chloromercuriphenol is readily available through the action of mercury(II) acetate, followed by sodium chloride, on 3,4-(methylenedioxy)phenol. 

The reaction of chromenes with mono- and bis- imides of 1,4-benzoquinones (6, X = O or NCOPh) is promoted by Lewis acids and affords pterocarpans and azapterocarpans, respectively (95TL2713). A total synthesis of the pterocarpan, neorautenane, involves a chemoselective coupling of a benzodipyran with o-chloro-mercuriophenol (95JCS(P1)949). 

The regioselective lithiation of 277 was used in the synthesis of the pterocarpans 4 -deoxycabenegrins A-I. 

As shown in the following scheme, a SEM-ether derived phenyl acetylene was treated with PtClj in the presence of CO to give a benzo[4>]furan, which was first subjected to desilylation, followed by Pd-catalyzed intramolecular etherification, affording the tetracyclic skeleton of pterocarpane family of phytoalexins <05JA15024>. A similar type of synthetic transformation was so applied to make a key intermediate in the total synthesis of vibsanol <05JA15022>. 2,3-Disubstituted benzo[h]furans were prepared under very mild reaction conditions by the Pd/Cu-catalyzed cross-coupling of various o-iodoanisoles and terminal... 

The results of screening legumes have often proved of systematic interest. For example, in the tribe Vicieae where over 60 species were examined, a major dichotomy emerged (Table 3). The genera Lathyrus and Pisum were united by the synthesis of plsatln and related pterocarpans. By contrast, members of Vicla and Lens uniformly accumulate furanoacetylenes, such as wyerone (13), a compound first characterized by Wain and his coworkers from broad bean in 1968 (14). 

As already observed in the triazolium-catalyzed benzoin reaction, electron-donating substituents (e.g. methoxy) lead to moderate to good enantiomeric excesses, up to 71%, whereas electron-withdrawing groups cause a strong decrease in enantioselectivity. Again, deactivation of the aldehyde function leads to lower catalytic activity but higher enantioselectivities. The chromanones accessible via this method are useful intermediates for the synthesis of pterocarpans [51, 52]. 

A different approach for the synthesis of racemic /rans-pterocarpans was also developed. A frans-fused 2-3-disubstituted dihydrobenzofuran was produced by AgBF,-promoted intramolecular cyclization, and after reduction of an ester function the six-membered oxygen ring was formed by Mitsunobu cyclization <01T7113>. 

Alternatively, chalcone reductase (CHR also known as deoxychalcone synthase) together with chalcone synthase and NADPH as a cofactor act in the formation of isoliquiritigenin, which is then isomerized, again by the enzyme chalcone isomerase, to form liquiritigenin, the precursor to daidzein, and the pterocarpan phytoalexins. A type II chalcone isomerase that seems to be found exclusively in the legumes catalyzes this isomerization reaction. Glycitein synthesis is not yet clearly defined, but is likely derived from liquiritigenin via flavonoid 6-hydroxylase, and an unidentified methyltransferase. 

The synthesis ( )-pterocarpan was achieved by the Heck coupling of 7-benzyloxy-2H-chromene with 2-iodophe-nol in [C4CiIm]PF6 and in the presence of the [PdCl2(PhCN)2]/Ph3P/Ag2C03. ... 

Synthesis, stereochemistry, structural classification, and chemical reactivity of natural pterocarpans (6H-benzofuro[3,2-r]chromenes) 13CRV 1614. 

Jimenez-Gonzalez, L., Garcia-Munoz, S., Alvarez-Corral, M., Munoz-Dorado, M. and Rodriguez-Garcia, I. 2006. Silver-catalyzed asymmetric synthesis of 2,3-dihydrobenzo-furans A new chiral synthesis of pterocarpans. Ghem. Eur. J. 12 8762-8769. 

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