Homologation, of ketone

The Homer - Emmons reagent (52) is effective in the one carbon homologation of ketones possessing acidic a-hydrogen atoms <96SL875> and electron-deficient alkenes add to 2-phenylseleno-l,3-dithiane in a photo-initiated heteroatom stabilised radical atom transfer process, giving products of considerable synthetic potential <96TL2743>. 

Alkylidenes (alkylidene carbenes) are valence isomers of alkynes. They have been prepared by alkyne pyrolysis, by homologation of ketones, and by generation of alkenyl anions bearing oc-leaving groups. Generated by any of these means, an alkylidene will insert intramolecularly into a remote C- H bond to form a new C—C bond and thus a cyclopentene. A concerted two-electron process, this reaction proceeds with retention of absolute configuration at the C - H site. 

A one-carbon homologation of carbonyl compounds is an important and extensively used method for the preparation of desired carbonyl compounds . One-carbon ring-expansion or one-carbon homologation of ketones or aldehydes via a S-oxido car-benoid is a representative example of the homologation, but few methods have been reported . 

Homologaton of ketones.3 The reagent is generally superior to diazomethane for homologation of ketones, particularly alicydic ones. The reaction with fluorcnone, followed by hydrolysis, gives 9-phenanthrol in 80% yield. 

Homologation of ketones. 1 Ketones undergo homologation when treated with trimethylsilyldia/omelhane in the presence of Bl , elherate. Yields are generally superior to those obtained with dia/omcthanc Another advantage is that the... 

Homologation of ketones to aldehydes cf. 9, 62-163), The reagent is particularly useful for conversion of an ot,p-unsaturated ketom, into the homologated p,y-unsaturated aldehyde (equation 1),... 

OL-Hydroxy aldehydes. A new method for one-carbon homologation of ketones to a-hydroxy aldehydes involves Darzens condensation with chloromethyl phenyl sulfone to give an ex,p-epoxy sulfone followed by ring opening by hydroxide ion. The anhydrous potassium hydroxide obtained by controlled addition of water to potassium /-butoxide (8,... 

Homologation of ketones (1, 369-370 6, 252-253 8, 222). Ethyl diazoacetate is recommended as the most useful diazoalkane for monohomologation of cyclic and acyclic ketones without formation of epoxides as by-products. One advantage is that the usually slow reaction can be catalyzed by BF3 etherate (or triethyloxonium tetrafluoro-borate). 

Homologation of ketones into their a-methoxylated homologs was originally reported by Trost [28a], HfCLt (or ZrCU) proved effective as a Lewis acid for the rearrangement step, giving good yields of the corresponding products (Eq. 25) [28b],... 

Acylation of primary amines and stereodiscrimination has been described (Eq. 35) [39], /S-hydroxysulfone rearrangement has been reported for homologation of ketones (Eq. 36) [40], and glycosylation mediated by glycosyl fluoride has also been reported (Eq. 37) [41]. 

Ketones.- A new synthesis of cyclopentadienes by the reactions of allylidenetriphenylphosphonium ylides (40) with a-halogenocarbonyl compounds has been reported.33 Wittig reactions of the ylide derived from the phosphonium salt (41) provide the hydrazones (42).34 This reaction combined with hydrolysis of (42) constitutes a method for the n-i-2 homologation of ketones and aldehydes (Scheme 8). 

The homologation of ketones by the addition of diazoalkanes complements the Tiffeneau-Demjanov rearrangement. Epoxide formation is a side reaction which can be minimized if polar aprotic solvents are avoided (Scheme 7). Rearrangement i.e. homologation) is maximized in ether solvents or by Lewis acid catalysis. The reaction is most effective in the ring expansion of cyclic ketones. 

Ethyl diazoacetate has been used extensively in the homologation of ketones to 3-keto esters. Lewis acid is required for the reaction (equation 23). ° There is a tendency for the least-substituted group to migrate, particularly if one group is fully substituted (equation 24). In a total synthesis of ( )-aplysin (20) this selective rearrangement was applied (Scheme 9), and a similar approach was used in a synthesis of (+)-hirsutic acid. Ethyl diazoacetate has also been used in the homologation of acyclic... 

Acetals. A one-step preparation of acetals by homologation of ketones under basic conditions is reported. 

Homologation of Ketones into Carboxylic Acids Badham. N.F. Tetrahedron 2004, 60,11. 

Alkynes. Deoxygenative homologation of ketones is accomplished simply by treatment with lithiated trimethylsilyldiazomethane. 

Homologation. The lower basicity of the anion derived from (1), compared with that of the dimethyl phosphonate, is useful for homologation of ketones containing acidic a-hydrogens, including cyclopentanone and P-tetralones. The products are ketene Jithioacetals. 

---