Cyclobutanones, from

Triisopropylbenzenesulfonyl hydrazones can be formed from cyclobutanones in very high yield.95... 

Acetalization with ethylene glycol under acidic conditions with azeotropic removal of water is the usual protection method for the carbonyl group. In one case the formation of the acetal of ethylene glycol was reported to be troublesome. In this case conditions reported in the first entry in Table 15 were used.317. Examples for the preparation of cyclobutanone acetals from cyclobutanones are given in Table 15. 

Thus the hemiketal from cyclopropanone will have 109.5° — 60° = 49.5°, and that from cyclobutanone 109.5° — 90° = 19.5° of strain at Cl. This change in the angle strain means that a sizable enhancement of both the reactivity and equilibrium constant for addition is expected. In practice, the strain elfect is so large that cyclopropanone reacts rapidly with methanol to give a stable hemiketal from which the ketone cannot be recovered. Cyclobutanone is less reactive than cyclopropanone but more reactive than cyclohexanone or cyclopentanone. 

The key steps in the ring expansion of the cyclobutanones (186) and (787) are the Baeyer-Villiger oxidation effected by H202—HOAc. It is noteworthy to point out that the Baeyer-Villiger oxidation is regiospecific and serves to be an excellent method for the preparation of y-lactone from cyclobutanones. 

P Volume 1,1991,283 pp. 109.50/ 69.50 ISBN 1-55938-180-9 CONTENTS Introduction to the Series An Editor s Foreword, Albert Padwa. Preface, Brian Halton. Strain in Organic Chemistry A Perspective, Brian Halton. Gem-Dihalocyclopropanes in Chemical Synthesis, Martin G. Banwell and Monica E. Re-um. 1-Halo- and 1, 2-Dihalocyclopropenes Useful Synthetic Intermediates, Mark S. Baird. Cyciization and Cycloaddition Reactions of Cyclopropenes, Albert Padwa and Glen E. Fryx-ell. New Synthetic Pathways From Cyclobutanones, Edward Lee-Ruff. Cyclic Alkynes, Enynes and Dienynes A Synthetic Challenge, Herbert Meier. Index. 

E. Lee-Ruff, New Synthetic Pathways from Cyclobutanones, in Advances in Strain in Organic Chemistry (B. Halton, Ed.) 1991, 1, Jai Press, Greenwich, CT. 

Ramnauth, J. and Lee-Ruff, E. (2001) Photochemical preparation of cyclopropanes from cyclobutanones. Canadian Journal of Chemistry, 79, 114-120. 

The enolate ions of ketones have become the most widely studied nucleophiles in SrnI reactions [21-23,40,66]. The enolate ions of acyclic and cyclic ketones (from cyclobutanone to cyclooctanone) [21,40] react with aryl and heteroaryl halides to afford the a-arylation products. No... 

The first step is straightforward—-just like the one you have just met. The pinacol dimer from cyclobutanone rearranges with the expansion of one of the rings to give a cyclopentanone fused spiro to the remaining fou(-membered ring. Reduction of the ketone then gives an... 

The behavior of the oxacarbenes derived photo-lytically from cyclobutanones is somewhat analogous to that exhibited by so-called nucleophilic carbenes (40). Dioxacarbene [92] (41), for example, is efficiently... 

More work on the nature of product formation from cyclobutanones, such as [79a], in inert solvents is required in order to better understand the fate of the presumed oxacarbene intermediate. At any rate, it is clear that ring expansion can occur in the absence of hydroxylic solvents, thereby eliminating a special role for protonic solvents. 

Solvent Dependence of Product Formation from Cyclobutanone Photolysis (313 nm Excitation)... 

Finally let us consider the very unusual bimolecular addition of dienes to cyclobutanones (34), a flagrant violation of Rule 7. The reactions which were run at -78 °C can be understood if we assume that the rate of cleavage of to a biradical is slowed down because of a decrease in the available thermal activation. However, a moderate yield of oxetane is formed from cyclobutanone and butadiene (19) at 10°C. From work on the quenching of fluorescence by alkanones (53), we anticipate the rate of... 

Only the triplet biradical from cyclobutanone would correspond to the biradical many chemists think of, i.e., one with a bond order of zero between and C2 and of 1 between C-j and C. ... 

Further reaction of Aese species with carbonyl compounds and hydrolysis of the resulting alkoxide leads to p-oxidoalkyl selenoxides which have been transformed into allyl alcohols on thermal decomposition (Schemes 51, 52 and 54, entry a see Section 2.6.4.4) or reduced to p-hydroxyalkyl selenides or to alkenes (Scheme 53). P-Oxidoalkyl selenoxides derived from cyclobutanones react in a different way since Aey rearrange to cyclopentanones upon heating (Scheme 54, b. Schemes 120 and 121 and Section 2.6.4.5.3). 

Pyrrolidine enamines of cyclic ketones have been prepared from cyclobutanone to cyclononanone. In the reaction of unsymmetrical 2-methyl or 2-phenyl cyclohexanone with pyrrolidine, of the two regio isomers 50a and 50b the less substituted enamine (50a) is formed preferentially . This is in contrast to the behaviour of enol derivatives, where the most stable regio isomer is the more substituted one. The reason for the destabilization of 50b is the steric interference of the 2-substituent with a CH2 group of the pyrrolidine ring in a coplanar cis arrangement at the C=C double bond. 

Raw and Taylor (04TL8607) have also exploited the reactivity of the transient s-cis-2-azabutadiene moiety in a cascade process for the synthesis of 4,5-dihydroazocines (Scheme 40). In this sequence, the strained dihydropyridines 119, formed from the reaction of 118 with an enamine derived from cyclobutanone and various secondary amines in situ, undergo disrotatory [4+2]-electrocyclic reaction to produce the trisubsti-tuted-4,5-dihydroazocines 120. 

Interestingly, the electrocyclic ring opening of dihydropyridines 119 is apparently slower than the intramolecular flZfl-Diels-Alder reaction depicted in Scheme 35. So, when triazine 118 is reacted with the enamine derived from cyclobutanone and diallylamine in situ, the tetracycle 114f is the sole product, isolated in quantitative yield (04TL8607) (Scheme 41). 

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