Single cyclobutanone

The fact that equatorial attack occurs exclusively, is deduced by consideration of the stereospecific ring enlargement into a single cyclobutanone inversion at the migration terminus is obtained upon treatment with europium(III). ... 

The same sequence was applied to 2-methacrolein (8). In this case a single cyclobutanone (9) was formed. This product was subjected to fragmentation of the corresponding cyclobutanol, which resulted in the unsaturated alcohol 10 in high yield. 

The ambivalent aptitude of sulfur [19] to stabilize adjacent anionic as well as cationic centers is a remarkable fact that has shown to be a reliable feature for the assembly of four-membered ring scaffolds utilizing cyclopropyl phenyl sulfides [20]. Witulski and coworkers treated the sulfide 1-69 with TsOH in wet benzene (Scheme 1.19) [21]. However, in addition to the expected cyclobutanone derivative 1-70, the bicyclo[3.2.0]heptane 1-70 was also obtained as a single diastereoisomer, but in moderate yield. Much better yields of 1-71 were obtained using ketone 1-72... 

Prochiral cyclobutanones with a single substituent at the 3 position proved to be poor substrates for this catalyst (132). Selectivities ranging from 26-47% ee are obtained, Eq. 112. The authors postulate that initial attack of the peracid on the car-... 

Ketene acetals and thioacetals can be used as ketene equivalents in cyclobutanone synthesis in situations where ketene to alkene cycloadditions are inefficient such as in the case of electron-deficient alkenes.14 Although thermal cycloadditions of ketene acetals and thioacetals with electron-deficient alkenes have been observed (see Section 1,3.2.1.), such cycloadditions proceed more efficiently and under milder conditions with metal catalysts. Efficient cycloadditions between ketene dimethyl acetal and alkenes substituted by a single electron-withdrawing group have been reported.15... 

Nucleophilic addition to four-membcred carbocycles is usually restricted to cyclobutanones. A typical example in this reaction category is the single-step chemospecific reaction of cyclobutanones 25, which afford masked 1,4-dicarbonyl compounds 26.58 63 Examples of compounds prepared in this manner can be found in Table 4.58... 

Ground-state triplet dicarbenes in photochemical systems have also been extensively studied by ESR. Dowd and coworkers (304) examined the interesting, frequently postulated ground triplet trimethylenemethane obtained by photolysis of either 4-methylene-A -pyrazoline or a single crystal of 3-methylene-cyclobutanone. This triplet molecule is axially symmetrical and the proton hyperfine splittings of 8.9 gauss observed in single-crystal experiments indicate that all protons in the molecule are equivalent when the axis perpendicular to the plane... 

Exploration of the tricyclic nucleus was initiated by oxidative cleavage of the cyclohexene double bond in the monoacetate (Scheme 36). The series of reactions shown served to prove the relationship of the 14-ene to the tetrasubstituted carbon atom. A similar oxidative sequence on decipi-14-ene (149) was employed to generate the ketone (152), which was shown to be a cyclobutanone with a single proton a- to the carbonyl group. Evidence for the presence of a cyclohexene ring, suggested from nmdr studies, was obtained by formation of the cyclohexenone... 

The synthesis of cyclobutanones can in some cases be accomplished more efficiently by addition of a ketene-iminium salt or a chromium carbene to an alkene. For example, under photochemical conditions, the chromium carbene 174 gave the cyclobutanone 175 as a single diastereomer (3.118). The product 175 was converted to the antifungal antibiotic (-l-)-cerulenin by way of the lactone 176. 

More recent approaches addressing dynamical effects on the reaction reveal a greater propensity for double inversion via mostly conrotatory motions over single inversion in the 1,2-dideuterio case by factors of 2.3-3.5 and 4.7, which are significantly less than that determined by Berson and Baldwin (refs. 21 and 22, respectively). Another significant milestone in the trimethylene story is the observation of the singlet species derived from photolysis of cyclobutanone and a determination of its lifetime before formation of cyclopropane at 122 fs. For the 2,2-dideuterio species the lifetime is 129 fs and that for the 1,1,3,3-tetradeuterio species is 183 fs. These effects were reasonably reproduced by DZP-TCSCF wave functions, which indicate that double inversion occurs four times more often by conrotatory over disrotatory paths. 

Substituted cyclobutanones have been converted to enantioenriched y-lactones by palladium-catalysed BV oxidation, using chiral phosphino-oxazoline ligands, giving yields up to 99% and 81% ee, rising to >93% ee through a single recrystallization. ... 

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