Ring expansion of cycloalkanones

Reduction, carboxyl groups, 56,83 Reduction of a,0-unsaturated p-toluene-sulfonyl-hydrazones to alkenes, 59,42 Reductive alkylation, 56,52 Reductive cleavage, 56, 101 Resolution of amines, 55,80, 83 Rexyn 201,55,4 Rhodium(III) oxide, 57, 1 Ring contraction, 56, 107 Ring expansion of cycloalkanones to cycloalkenones, 59, 113... 

ONE-CARBON RING EXPANSION OF CYCLOALKANONES TO CONJUGATED CYCLOALKENONES 2-CYCLOHEPTEN-l-ONE... 

Ring expansion of cycloalkanones.1 The hypoiodite reaction can also be used for a four-atom ring expansion of cyclic ketones via the corresponding lactols (cf., 13, 150). 

Scheme II/6. Ring expansions of cycloalkanones by diazo reagents.

Ring expansion of cycloalkanones. 1-Trimethylsilyloxybicyclo[n.l.0]alkanes (1), prepared by Simmons-Smith reaction with silyl enol ethers of cycloalkanones, react with ferric chloride in DMF containing pyridine to form a 3-chlorocycIo-alkanone (2) in fair to high yield. Dehydrochlorination (sodium acetate) yields a 2-cycloalkenone (3) containing one more carbon atom than the starting cycloalkanone. 

Radical-mediated ring expansion of 2-halomethyl cycloalkanones. 

Riiedi et al. discovered a novel and efficient two-carbon ring expansion of vinylcycloalkanones 148 (Scheme 32). Precursors with n = 9 to 15 were ther-molysed at 600-630 °C to generate diradical intermediates, which took part in intramolecular recombinations to yield ring-expanded y,8-imsaturated cy-cloalkanones 149 [120]. In each case a mixture of E and Z isomers was obtained. Thermolysis of the 12-membered-ring ethynyl-substituted cycloalka-none 149 yielded a novel 14-membered-ring allenyl-cycloalkanone 150 via an analogous mechanism. 

It is not essential to use mono- or dihalocyclopropane derivatives. Ring expansion of methylene adducts, i.e. l-(trimethylsiloxy)bicyclo[n.l.O]alkanes 14, can be accomplished with a reagent consisting of iron(III) chloride in pyridine and dimethylformamide. In this process, p-chlorocycloalkanones 15 are the initial products of ring cleavage, but they are most conveniently converted to cycloalkanones 16 by refluxing with sodium acetate in methanol. ... 

One-carbon ring expansion of 2-substituted cycloalkanones 37 (usually / -oxo esters) via transient bicyclo[n. 1.0]alkan-l -oxyl radicals 39 has been extensively exploited as a method of making medium and large ring cycloalkanones 40. " One-carbon ring expansion was also performed with bicyclo[5.3.0]decan-2-ones 41 giving 42 as the product. 

Xie ZF, Suemune H, Sakai KJ (1988) Synthetic Approach to Medium-sized Cycloalkanones. A One-pot Three-carbon Ring Expansion of Carbocyclic p>-Keto Esters. J Chem Soc Chem Commun 612... 

Photolysis of 2-(2 -cyclopropylcyclopropyl)cycloalkanones (108 n = 1, 2) gave ring-expanded products e.g. (108 n = 1) gave a mixture of cyclododecanone (61 %) and 2-cyclopropylcyclononanone (20%). Ring expansion of cyclic mono- and diacetylenes by 4, 8 or 12 carbon atoms can be achieved by nickel-catalysed cyclooligomerization with buta-1,3-diene, followed by oxidative cleavage thus cyclo-tetradec-l,8-diyne was converted into cyclotriacontane. ... 

Scheme 6 First ring expansion of a 2-substituted cycloalkanone...

I, 3-Cycloalkadiones have been prepared by ring expansion of 2-hydroxy-2-methoxymethyl cycloalkanones [equation (56)]. ... 

Ring expansion.1 The adducts (2) of cycloalkanones with 1 on reaction with methyllithium or wc-butyllithium at 0° rearrange to ring-expanded a-phenylthio ketones. 

The procedure described is a simple, rapid, and convenient method for conversion of n-sized cycloalkenones into n+4 alkenolides. Significant but limited progress has been reported in the recent literature toward the preparation of medium and large ring lactones via ring-expansion reactions. One of the most notable and useful developments in this area involves conversion of a cycloalkanone into a bicyclic vinylic ether which is oxidatively cleaved to form a ring-enlarged keto lactone.3... 

At the same time the conversion of 11/54 — 11/59 (Scheme II/9) was published, an alternative way was found, which is summarized in Scheme II/9. The lithium derivative of (phenylthio)methyl phenyl sulfone adds nearly quantitative into ketones, in the presence of diethylaluminium chloride. The rearrangement (e.g. 11/61—> 11/62) proceeds smoothly on treatment of the tertiary alcohol, 11/61, with an approximately sixfold excess of diethylaluminium chloride [46]. An alternate reagent, the lithium salt of methoxy methyl phenyl sulfone, in a similar reaction yielded, enlarged a-methoxy cycloalkanones. The latter reaction sequence is restricted to the expansion of four- and five-membered rings [46]. 

Ring enlargement reactions also take place in 2-oxocycloalkane-l-carbonitri-les substituted in 1-position by an co-alkylester or ketone [17]. The introduction of cyano groups into the a-position of cycloalkanones can be carried out in CH2C12 with C1S02NC0 in dimethylformamide [18]. Two and three carbon atom ring expansion reactions are possible by this method. In most cases the yields are low, which is in contrast with the results of the lactonisation (compare... 

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