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Butenolide formation

The acetogenin (+)-solamin and analogs were prepared via a ruthenium-catalyzed Alder-ene reaction/butenolide formation (Scheme 37).96 Of particular note is the ability of the ruthenium to catalyze the reaction in the presence of free hydroxyls, sulfides, and sulfones. Yields ranged from 65% for the sulfide to 88% for the sulfone. Trost has also applied this reaction to the total synthesis of (+)-ancepsenolide, which features a bis-Alder-ene reaction (Scheme 38).97... [Pg.595]

Chiral Rh(II) oxazolidinones Rh2(BNOX)4 and Rh2(IPOX)4 (25a,b) were not as effective as Rh2(MEPY)4 for enantioselective intramolecular cyclopropanation, even though the steric bulk of their chiral ligand attachments (COOMe versus i-Pr or CH2Ph) are similar. Significantly lower yields and lower enantioselectivides resulted from dinitrogen extrusion from prenyl diazoacetate catalyzed by either Rh2(4.S -lPOX)4 or Rh2(4S-BNOX)4. This difference, and those associated with butenolide formation [91], can be attributed to the ability of the carboxylate substituents to stabilize the carbocation form of the intermediate metal carbene (3b), thus limiting the Rh2(MEPY)4-catalyzed reaction to concerted carbene addition onto both carbon atoms of the C-C double bond. [Pg.213]

Scheme 4.8. Butenolide formation from gem-dihalocyclopropanecarboxylic acids. Scheme 4.8. Butenolide formation from gem-dihalocyclopropanecarboxylic acids.
Scheme II Butenolide Formation in Catalytic Intramolecular Cyclopropanation... Scheme II Butenolide Formation in Catalytic Intramolecular Cyclopropanation...
Interactive mechanism for palladium-catalysed carbonylative butenolide formation... [Pg.1085]

The butenolide formation proceeds even in the absence of Ag salt [155]. The furan 407 was obtained directly by the reaction of methyl 2,3-alkadienoate... [Pg.163]

Efficient Synthesis of Cardenolides. A general and efficient method has been described for the synthesis of cardenolides, consisting of (1) a-methylsulfenylation of pregnen-20-one, (2) Refor-matsky reaction, and (3) butenolide formation by alumina chromatography of the epoxy ester obtained from the S-methylated Reformatsky product (eq 4). ... [Pg.398]

The strategy for the conversion of 140 into securinine (1) was essentially the same except for the oxidation step, which required softer conditions (Scheme 22). Interestingly, lower yields were observed for the butenolide formation in the securinine series (0.1% overall yield, 18 steps). [Pg.74]

Along with the structural elucidation of nirurine (45), Cordell and coworkers proposed a plausible biosynthetic pathway leading to this compound (Scheme 46). One of the key features of this mechanism was the involvement of a dopamine-building block instead of the usual tyrosine precursor for the elaboration of the CD rings. Thus, the cormection of ornithine unit (266) to dopamine (267) could give rise to intermediate 268 after butenolide formation. Then, attack of the nitrogen to the carbonyl moiety followed by reduction of the C8—C9 double bond and elimination of a molecule of water would furnish compound 43. Finally, a nucleophilic attack of the C8—OH onto the corresponding C5—N1 iminium ion of 43 would deliver nirurine (45). [Pg.100]

Pd hydride. Subsequent enolate formation, double bond isomerization, and carbonylation give the butenolide 582. [Pg.208]

The reaction of vinyloxiranes with malonate proceeds regio- and stereose-lectively. The reaction has been utilized for the introduction of a 15-hydroxy group in a steroid related to oogoniol (265)(156]. The oxirane 264 is the J-form and the attack of Pd(0) takes place from the o-side by inversion. Then the nucleophile comes from the /i-side. Thus overall reaction is sT -StM2 type, in the intramolecular reaction, the stereochemical information is transmitted to the newly formed stereogenic center. Thus the formation of the six-membered ring lactone 267 from 266 proceeded with overall retention of the stereochemistry, and was employed to control the stereochemistry of C-15 in the prostaglandin 268[157]. The method has also been employed to create the butenolide... [Pg.325]

Triethylammonium formate is another reducing agent for q, /3-unsaturated carbonyl compounds. Pd on carbon is better catalyst than Pd-phosphine complex, and citral (49) is reduced to citronellal (50) smoothly[55]. However, the trisubstituted butenolide 60 is reduced to the saturated lactone with potassium formate using Pd(OAc)2. Triethylammonium formate is not effective. Enones are also reduced with potassium formate[56]. Sodium hypophosphite (61) is used for the reduction of double bonds catalyzed by Pd on charcoal[57]. [Pg.520]

Hydroxymethylene formation proceeded in the standard fashion (7 ) to give a 93% yield of 22. Carcinogenic hexamethyl-phosphoric triamide was replaced by N-methylpyrrolidone as the solvent for the condensation reaction of 22 with the bromo-butenolide 23 in the presence of excess K.CO. and gave a mixture of racemic strigol (1) (35%) and 4 -epistrigol (25) (39%), which were readily separated by chromatography on silica gel. [Pg.442]

Fiandanese and coworkers [103] described a new approach for the synthesis of the butenolides xerulin (6/1-207) and dihydroxerulin (6/1-208), which are of interest as potent noncytotoxic inhibitors of the biosynthesis of cholesterol (Scheme 6/1.53). The key transformation is a Pd°-catalyzed Sonogashira/addition process of 6/1-204 or 6/1-206 with (Z)-3-iodo-2-propenoic acid 6/1-205, which is followed by the formation of a lactone to give 6/1-207 and 6/1-208, respectively. [Pg.393]

The total synthesis of (+)-asimicin also uses this methodology for the introduction of the butenolide in one of the final steps, the formation of 117 from 116 (Scheme 15.34) [78], Owing to the small scale (18 pirn o 1), an excess of catalyst had to be used. [Pg.895]

Anomalous reactions are reported for some butenolides. Thus compound 46 does not cyclize in the expected manner [130]. Formation of the observed products can be rationalised on the assumption that electrogenerated base can interact with... [Pg.79]

The nucleus of the one-time widely prescribed prescribed COX-2 inhibitor, rofecoxib, better known by its trade name Vioxx , actually comprises a butenolide rather than a classical heterocycle. The drug was withdrawn from the market at full flood due to an unexpectedly high incidence of adverse cardiovascular side effects. The compound is included at this point to emphasize the breadth of the SAR for COX-2 anti-inflammatory agents. Reaction of phenylacetic acid (35-1) with ethyl bro-moacetate in the presence of triethylamine leads to the formation of the ester (35-2). Treatment of that intermediate with a strong base generates a carbanion at the benzyhc position in an intramolecular reaction, this attacks the terminal ester carbonyl to yield the butenolide (35-3). Reaction of that compound with triflic anhydride converts the... [Pg.261]


See other pages where Butenolide formation is mentioned: [Pg.180]    [Pg.55]    [Pg.496]    [Pg.258]    [Pg.329]    [Pg.16]    [Pg.258]    [Pg.1349]    [Pg.1350]    [Pg.1349]    [Pg.1350]    [Pg.180]    [Pg.55]    [Pg.496]    [Pg.258]    [Pg.329]    [Pg.16]    [Pg.258]    [Pg.1349]    [Pg.1350]    [Pg.1349]    [Pg.1350]    [Pg.4]    [Pg.355]    [Pg.142]    [Pg.126]    [Pg.20]    [Pg.100]    [Pg.399]    [Pg.937]    [Pg.13]    [Pg.4]    [Pg.323]    [Pg.861]    [Pg.33]    [Pg.620]   
See also in sourсe #XX -- [ Pg.131 ]




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