Cyclobutanone, acidity

There is some spectral evidence that acylation of enamines of cyclic ketones with acid chlorides having an a-hydrogen in the presence of triethylamine proceeds via the ketene and subsequent cycloaddition (84). The intermediate cyclobutanone is then opened to give the enamino ketone which is hydrolyzed to the 2-acyl cyclohexanone. In the case of enamines of larger cyclic ketones the alternate mode of the cyclobutanone opening predominates, with the formation of ring-expanded 1,3-diketones upon... 

Abstract The photoinduced reactions of metal carbene complexes, particularly Group 6 Fischer carbenes, are comprehensively presented in this chapter with a complete listing of published examples. A majority of these processes involve CO insertion to produce species that have ketene-like reactivity. Cyclo addition reactions presented include reaction with imines to form /1-lactams, with alkenes to form cyclobutanones, with aldehydes to form /1-lactones, and with azoarenes to form diazetidinones. Photoinduced benzannulation processes are included. Reactions involving nucleophilic attack to form esters, amino acids, peptides, allenes, acylated arenes, and aza-Cope rearrangement products are detailed. A number of photoinduced reactions of carbenes do not involve CO insertion. These include reactions with sulfur ylides and sulfilimines, cyclopropanation, 1,3-dipolar cycloadditions, and acyl migrations. 

The oxidation by chromic acid alone leads to a mixture of cyclobutanone and 4-hydroxybutyraldehyde the existence of an isotope effect for the oxidation of I-deuteriocyclohexanol suggests that Cr(VI) produces the ketone and lower oxidation states of chromium produce the cleavage product. 

Sulfur ylides can also transfer substituted methylene units, such as isopropylidene (Entries 10 and 11) or cyclopropylidene (Entries 12 and 13). The oxaspiropentanes formed by reaction of aldehydes and ketones with diphenylsulfonium cyclopropylide are useful intermediates in a number of transformations such as acid-catalyzed rearrangement to cyclobutanones.285... 

The same epoxide 335 was easily obtained in mild conditions (0°C, 5 min) by m-ehloroperbenzoic acid oxidation [13b]. Epoxidation of alkylidenecyclo-propanes by m-chloroperbenzoie acid has been greatly exploited as a route to the synthesis of cyclobutanones 638 via the well known ring expansion of oxaspiropentanes 637 (Scheme 98) [176,177,8]. 

CsF induces the ring-opening cyclization of the thus obtained l-[2-(trimethylsilylmethyl)cyclopropylcarbonyl] imidazole 154 with diethyl fumar-ate or diethyl maleate to give the cyclobutanone 155 [80], The facile ring fission of 154 also occurs in the presence of BF3OEt with the formation of the corresponding y,<5-unsaturated carboxylic acid. (Scheme 55)... 

Cyclobutanones react with arylboronic acids to afford butyrophenones (Equation (60)). Addition of arylrhodium species to the carbonyl group followed by /3-carbon elimination is proposed. 

These electrophilic conjunctive reagents require donor reactants. The cyclopropyl-carbinols as precursors to cyclobutanones arise by simple addition of organometallics. For example, the cyclobutanone 47 derives by addition of vinyllithium to 44 followed by rearrangement with aqueous fluoroboric acid 92). In some cases, this route to cyclopropylcarbinols is preferred. Addition of 41 to aldehydes or ketones... 

A bis-vinylogue of a cyclopropylcarbinol 57 arises by standard transformations (Eq. 59) from the Peterson olefination product 56. Here too, acid induced rearrangement proceeds exclusively to the cyclobutanone and not to larger ring products93). 

Indeed, exposure of the vinylcyclobutanone 67 to acid produces the perhydro-azulene skeleton 68 as summarized in Eq. 78 112). With more ready access to the types of substituted cyclobutanones required for this lateral cyclopentannulation (see substitutive spiroannulation), milder conditions and thus better processes will probably ultimately be developed. 

Treatment of the adducts of 30 and ketones with excess HC1 in the presence of a Lewis acid leads directly to an acyclic system as in 85 (Eq. 105) 122). It is likely that the thiophenol liberated in the ring expansion to the cyclobutanone 86... 

The availability of cyclopentenones from butanolides allows the lactone annulation to facilitate the synthesis of cyclopentyl natural and unnatural products. An example that highlights the latter is dodecahedrane (178) for which 179 constitutes a critical synthetic intermediate 136,137). Lateral fusion of cyclopentenones as present in 179 can arise by acid induced reorganization and dehydration of 180. While a variety of routes can be envisioned to convert a ketone such as 182 into 180, none worked satisfactorily137 On the other hand, the cyclobutanone spiro-annulation approach via 181 proceeds in 64 % overall yield. Thus, the total carbon cource of dodecahedrane derives from two building blocks — cyclopentadiene and the cyclopropyl sulfonium ylide. 

The cyclobutanone (255) reacted with acid to furnish the keto-acid (259). Upon esterification, ketalization and reduction, (259) was converted to the alcohol (260). Mesylation of the alcohol (260) and then treatment of the mesylate with NaN3 in DMSO provided the azide (261). The azide (261) was then transformed to the urethane (262) by reduction and ethyl chloroformate reaction. The urethane (262) was deketalized by acid, nitrosated by N204—NaOAc and decomposed by NaOEt—EtOH to give the ketone (263) 89). The ketone (263) served as a starting material for the synthesis of veatchine (264)90). 

Subjection of the mixture of cyclobutanones rac-43 and rac-44 to mild acidic conditions resulted in the rearrangement of cyclobutanone rac-43 to its more stable isomer rac-45, whereas rac-44 remained unchanged. The ob-... 

In the same year, chiral phosphoric acids were found to catalyze the enantioselective Baeyer-ViUiger (BY) oxidation of 3-substituted cyclobutanones 140 with aqueous... 

Cyclobutanedicarboxylic acid, with sulfuryl chloride to give 3-chloro-1,1 -cyclobutanedicarbox-ylic acid, 51, 73 CYCLOBUTANONE, 51, 76 CYCLOBUTENE, CW-3-4-DICHLO-RO, 50, 36... 

This modification of the Curtius reaction has been used extensively in many laboratories and has been found to be generally applicable. Some examples from the literature include the stereoselective synthesis of a wide variety of cyclopropylamine derivatives from the corresponding acids,11-13 the stereoselective preparation of some substituted norbornylamines from easily isomerized acids,14 the preparation of some 1-aminocyelobutancearboxylic acids from the corresponding acid esters,18 the preparation of a substituted cyclobutanone from... 

The Cj - and 54-symmetric tetraesters of tricyclo[3.3.0.0 ]octane (430 and 431) have been prepared by oxidation of diene 429 To access the parent hydrocarbon (435), acid chloride 432 was transformed to the derived ketene which undergoes intramolecular [2+2] cycloaddition The resulting cyclobutanone (433) serves as precursor to perester 434 whose thermal decomposition proceeds with chain transfer in competition with cleavage The unique arrangement of the carbon atoms in 435 is such that the smallest rings are all five-membered. The highly symmetric structure may be viewed as a constrained cisoid bicyclo[3.3.0]octane (as well as the symbol of NATO). 

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