Paniculides, synthesis

The key step in Smith s paniculides synthesis was the oxidation of the cyclobutanone (198) to the epoxylactones (199) and (200), which were separated by flash chromatography 69). 

Panfuran — see 1,2,4-Triazine, 3-amino-6-[(5-nitro-2-furyl)vinyl]-Paniculide C synthesis, 1, 446 Pansoil ... 

For the construction of oxygen-functionalized Diels-Alder products, Narasaka and coworkers employed the 3-borylpropenoic acid derivative in place of 3-(3-acet-oxypropenoyl)oxazolidinone, which is a poor dienophile in the chiral titanium-catalyzed reaction (Scheme 1.55, Table 1.24). 3-(3-Borylpropenoyl)oxazolidinones react smoothly with acyclic dienes to give the cycloadducts in high optical purity [43]. The boryl group was converted to an hydroxyl group stereospecifically by oxidation, and the alcohol obtained was used as the key intermediate in a total synthesis of (-i-)-paniculide A [44] (Scheme 1.56). 

With Tartrate-Derived Chiral 1,4-Diol/Ti Complexes A catalytic asymmetric Diels-Alder reaction is promoted by the use of a chiral titanium catalyst prepared in situ from (Pr O TiC and a tartrate-derived (2.R,3.R)-l,l>4,4-tetraphenyl-2,3-0-(l-phenylethylidene)-l,2,3,4-butanetetrol. This chiral titanium catalyst, developed by Narasaka, has been successfully executed with oxazolidinone derivatives of 3-borylpropenoic acids as P-hydroxy acrylic acid equivalents [40] (Eq. 8A.21). The resulting chiral adduct can be utilized for the first asymmetric total synthesis of a highly oxygenated sesquiterpene, (-i-)-Paniculide. 

The reagent (2) has been used for a total synthesis of paniculide A (4), a highly oxygenated bisabolene, by annelation of methyl a-formylpropionate with 2 followed by dehydration.2... 

Selective deprotection of a MOM ether in the presence of an acid labile p-methoxybenzyl ether was accomplished as part of a synthesis of Paniculide.447 Treatment of 241.1 [Scheme 4.241] with methanolic HQ at 0 °C for 4 days lib-... 

Jacobi extended this methodology for the synthesis of the novel sesquiterpene ( )-paniculide A (528) (Scheme 66) (84TL4859). Thermal cycloaddition of 518 in ethylbenzene in a similar condition afforded the methoxyfuran 520 in 94% yield through the intermediate 519. Phenylselenation of 520 with LDA and phenylselenyl chloride gave a 1 1 mixture of phenylselenides 521, which upon kinetic deprotonation-protonation afforded the a-isomer (522) in... 

Jacobi s synthesis of ( )-paniculide-A involves an intramolecular Diels-Alder reaction of the alkynic ketone (31). This compound was prepared in >90% yield (Scheme 9) by acylation of a lithium alkynide with the A7-methoxy-A7-methylamide (30). Addition of the anion to other derivatives related to (30) such as an acid chloride, a trifluoroacetic mixed anhydride, an acyl imidazole, S-(2-pyridyl) thiolates and a mixed carbonic anhydride (from ethyl chloroformate) led to either bis-addition or to proton abstraction. Notice should be made of the stability exhibited by the A7-methoxy-A7-methylamide group while the oxa-zole moiety was being introduced. ... 

Amano, S., Takemura, N., Ohtsuka, M., Ogawa, S., Chida, N. Total synthesis of paniculide Afrom D-glucose. Tetrahedron 1999, 55, 3855-3870. 

Narasaka and Yamamoto applied catalyst 406 in the cycloaddition of 1-aceto xy-3-methyl-1.3-butadiene (409) to 3-boryl propenoic acid derivative 410 (equation 122). Cycloadduct 411 was employed in the total synthesis of (-fl-paniculide ". ... 

As noted in Scheme 38,3-borylpropenoic acid derivative 45 functions as an effective dienophile with several butadienes [108]. The impetus for the development of this particular dienophile was the low reactivity observed for the corresponding 3-acetoxypropenoic acid derivative. Subsequent to cycloaddition, the boryl moiety may be stereospecifically oxidized to the corresponding alcohol and, as such, dienophile 45 effectively functions as a P-hydroxyacrylic acid surrogate. An asymmetric synthesis of (-l-)-paniculide A relied on this strategy as the key transformation [109]. 

Synthesis of Evodone Synthesis of Ligularone and Petasalbine Synthesis of Paniculide-A Synthesis of Gnididione Synthesis of Norsecurinine Synthetic Approach to Geigerin Synthesis of Stemoamide Thiofurans and Amidofurans... 

Paniculide-A is structurally the least complicated of the paniculides, a family of highly oxygenated sesquiterpenes from Andrographis paniculata. Jacobi s synthesis of paniculide-A began with a four-step conversion of 3-methyl glutaric anhydride 175 to the oxazole acetylenic ketone 176 (Fig. 3.54). Cycloaddition of... 

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