Ring synthesis coumarin

Cupric sulfate Coumarin ring synthesis CuSQj o... 

Zn-carbonate and NaHCOg ground together, suspended in methylene chloride, 2-carbethoxy-3-bromocyclopent -2- enone and 3a, 4-dihydroxy-6-methoxy-3a, 8a-di-hydrofuro[2,3-b]benzofuran added, and stirred 20 hrs. at room temp, under Ng rac. aflatoxine M. Y 32%. - This new coumarin ring synthesis is particularly useful with acid-sensitive phenols, when the classical Pedimann synthesis is not applicable. F. e. s. G. Biichi and S. M. Weinreb, Am. Soc. 93, 746 (1971). 

Pyrid inel anil ine Coumarin ring synthesis... 

One of the hits found in the Chem Inform reaction database is shown in the window for reaction substructure searches in Figure 10.3-55. It fits the synthesis problem perfectly, since in the synthesis direction it forms the coumarin ring system directly, in one step. 

Ring synthesis of coumarins 9.3.2. / From phenols and 1,3-ketoesters... 

The Pechmann condensation also played a key role in the Biichi group s efforts toward the total synthesis of aflatoxin Bi (44). In this work, the central coumarinic ring system of aflatoxin was prepared by condensing the racemic tricyclic phenol 40 with ethyl methyl-3-oxoadipate (41) in methanolic HCl at 5 °C to provide tricycle 42 in 57% yield. The use of methanol as a solvent was crucial to the success of this reaction, as attempts to perform this reaction in sulfuric acid led to the rapid isomerization of 40 to the corresponding benzofuran-3-acetic acid, which could be converted to the analogous coumarin product only in very poor yield. Subsequent cyclization of the pendant ester moieties of 42 afforded pentacyclic lactone 43. Treatment of 43 with disiamylborane resulted in selective reduction of the dihydrofuranone to the corresponding hemiaminal, which was then acetylated and pyrolyzed (240 °C) to provide ( )-aflatoxin Bi (44). 

Owing to exceptional sensitivity of the tricyclic phenol (A) to acidic reagents, direct condensation with 2-carbethoxycyclopentane-l,3-dione (i) under von Pechmann coumarin synthesis conditions proved impossible. However, the bromide (ii) readily underwent condensation to give the desired coumarin ring D when zinc carbonate was used both as catalyst and acid scavenger. 

Coumarin is usually prepared by heating salicylaldehyde with acetic anhydride and sodium acetate (i.e., the Perkin cinnamic acid synthesis, p. 23 6), whereby the 0" hydroxy-cinnamic acid (I) undergoes cyclisation to coumarin. Coumarins having substituents in the benzene ring can often be similarly prepared. 

The Pechmaim reaction has found extensive appHcations for the synthesis of numerous coumarin derivatives (39). Coumarin derivatives substituted in the pyrone ring can be obtained by condensing phenol with beta-ketoesters. For example, 4-methylcoumarin (3) is obtained with ethyl acetoacetate... 

Synthesis of the coumarin derivative 11.58 containing two isomeric triazolyl rings is indicated in Scheme 11.24- The substituted pyrazolyl derivative of naphthalimide 11.59 is prepared by a reaction sequence somewhat similar in principle to that already shown in Scheme 11.14, using 4-amino-1,3,5-trimethylpyrazole in the penultimate step followed by quaternisation. 

A review of Claisen rearrangements in aqueous solution has appeared. The synthesis of natural products utilizing tandem Diels-Alder additions with sigmatropic rearrangement processes has been reviewed, and a brief review of the regioselective synthesis of coumarins, quinolones and thiocoumarins with 3,4-fused pyran or furan ring systems by the Claisen rearrangement has been presented. ... 

In the early 1970 s potent acaricidal activity in 3-aryl-4-hy-droxy-coumarins. III, and 2-aryl-l,3-indanediones, IV, and their enol esters was discovered at Union Carbide (1,2). Extensive synthesis and screening of analogs in the dione and enol ester series led to the field test candidates Va and Vb, active against both motile forms (mite) and eggs. Va and Vb embodied certain structural and physicochemical features shown by published QSAR studies (2,3) to be important in determining the level of activity in the 1,3-indanedione series (1) the dimension D2 across the aryl ring must be near 7A and symmetry is preferred (2) the... 

Several reports for the synthesis of coumarins have used lactone formation to erect the tricyclic core (Equation 44) < 1995T3197,1999SC929>. Other approaches to similar coumarins include the ring opening of an epoxide (Equation 45) <2002TA1799>. 

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