2.3- disubstituted cyclobutenone

Chloro-2,3-disubstituted cyclobutenones undergo a Pd-assisted cross coupling with 2-stan-nylated furans subsequent heating to 100°C gives 4-hydroxybenzo[6]furans (Equation (65)) <93JOC3550>. 

The rhodium-catalyzed reaction of 2,3-disubstituted cyclobutenone 89 with electron-deficient alkenes dehvered 2,3,6-substituted phenols 90 (Scheme 3.51) [60]. 

Disubstituted 4-chloro-2-cyclobutenones 75 undergo the palladium-catalyzed cross-coupling reaction with vinyl- and arylstannanes 76 or vinylzir-conium reagents to give the 4-R sa,-2-cyclobutenones 77. Without isolation, these cyclobutenones 77 are rearranged to the substituted phenols 78 on thermolysis [38], Application of this method to the stannylated heteroaromatics 79 provides a synthetic route to the aromatic benzoheterocycles 80 [39]. (Scheme 27 and 28)... 

Cyclobutenones. Cyclobutenones and cyclobutenediones undergo photochemical rearrangement to unsaturated acids in a manner analogous to that of 6,6-disubstituted-2,4-cyclohexadienones. Irradiation of Formula 133 in ether saturated with water gives Formula 134 (49). In... 

Not surprisingly, cyclobutenones have also been isolated from reactions of chromium a/Arj /alkoxycarbenes, where no competing jc-system is present [49], and from Qo -disubstituted arylalkoxylcarbenes in which bond formation to the arene is blocked [50]. By contrast. 

Naphthoquinones from cydobutenediones (13,97-98 209-120 14, 253-254 16, 102). Liebeskind et al. have developed a stereocontrolled route to 2,3-disubstituted quinones from 2-alky -3-a koxycyclobutenediones (1). Thus addition of ArLi to 1 followed by methylation provides 2 in 50-75% yield. Reaction of 2 with RLi followed by a quench with trifluoroacetic anhydride and NH4CI provides the cyclobutenone 3. These products are converted into quinones 4 by pyrolysis at 140 followed by oxidation (CAN). 

Tin Derivatives. A regiocontrolled method for construction of substituted benzofurans, dibenzofurans, benzothiophenes, and dibenzothiophenes uses 4-chloro-2,3-disubstituted-2-cyclobutenones as reactants together with a heterocycle (Scheme 17). In the construction... 

Pd(PhCN)2Cl2-catalyzed reaction of 4-chloro-2,3-disubstituted-2-cyclobutenones with aryl or 1-alkenylstannane reagents afforded substituted benzannulated heteroaromatics (eq 19). This process was designed to provide 4-vinylic- (or arylic- or heteroarylic-) cyclobutenones via a palladium catalyzed cross-coupling reaction. The cross-coupled products, in turn, would be transformed to substituted phenols upon thermolysis. 

Acyclic y-epoxy-sulphones have been converted into cyclobutenones (Scheme 28)while cyclic /8-epoxy-sulphones have been used for the synthesis of a,/8-disubstituted cyclopentenones (Scheme 29). 

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