1,2-transposition of a carbonyl group

Alkylative 1,2-transposition of a carbonyl group is also possible (equation I). ... 

Transpositions of a carbonyl group. An a-sulfenylated ester (1), prepared as described above, can be reduced by lithium aluminum hydride in THF at 25° in high yield to the alcohol (2). Treatment with thionyl chloride (benzene or ether) yields the primary chloride (3), which can be dehydrohalo-... 

Transposition of C=0 groups. A method for 1,2-transposition of a carbonyl group is shown in equation (I). A method for 1,2-transposition of a carbonyl group with alkylation is illustrated in equation (II). ... 

The anodic a-acetoxylation or a-medioxylation of ketones has been shown to be a powerful tool for the 1,2-transposition of the carbonyl group. The overall process is described by equation (24). ... 

A regioselective 1,2-transposition of the carbonyl group has been performed on 3-phenyl-5-bromo-4(5//)-isoxazolone, in the presence of thiourea, leading to 3-phenyl-5(4//)-isoxazolone <2003IJB2625>. 

Carbonyl transposition. The last steps in a total synthesis of dl- y-coramine (5) required a 1,2-transposition of the carbonyl group of 2. This was accomplished by bissulfenylation of the lithium enolate of 2 with phenyl ben-zenethiosulfonate (1). The carbonyl group of the product was reduced and the... 

Application of the MVK annulation procedure to enamines of acyclic ketones and aldehydes gives cyclohexenones. If the aldehyde carbonyl group is attached to a ring, the procedure provides a valuable stereoselective method for the spiroannulation of cyclic ketones (Scheme 138). The use of l-methoxybut-3-en-2-one in place of MVK provides a means for subsequent 1,2-transposition of a ketone carbonyl function (Scheme 139). Condensation of 2,2,2-trifluoroethyi vinyl ketone with enamines gives 2-trifluoromethylcyclohexenones °. 

Carhonyl shift via ally lie sulfides.2 A method for transposition of the carbonyl group of a, /J-enones to either the a- or a - position is illustrated in equation (I) for the tosylhydrazone of 3-methyl-2-cyclohexenone. 

Nucleophilic addition to a,P-epoxysilanes is part of a reaction sequence which has been used to effect 1,2-transposition of carbonyl groups (Figure Si5.14). 

The a-alkylation of sulfonylhydrazone dianions with disulfides followed by Shapiro reaction has been used to effect the 1,2-transposition of carbonyl groups.19,20 As shown below, treatment of tosylhydrazone 31 with n-BuLi/TMEDA followed by addition of dimethyl disulfide and deprotonation with an additional equivalent of w-BuLi provided vinylsulfide 32.19 Exposure of this compound to mercuric chloride in hot aqueous acetonitrile provided ketone 33 in 75% overall yield. 

In order to transform (259) into amarolide (267), there were three points to be considered i) the transposition of the carbonyl group from C-3 to C-l position (259 — 264), if) the hydroxylation at C-2 and C-l 1 positions, both with the introduction of an a-equatorial hydroxyl group (264 —> 265), and Hi) the oxidation of the oxane D-ring to give the 8-lactone moiety (265 —> 267). 

An expeditious stereospecific synthesis of the protoilludane skeleton has been actively pursued by Matsumoto s group. In his first approach (Scheme 42),307 bicyclooctanone 274 was smoothly elaborated in classical fashion. Using a five-step sequence to effect a 1,2-carbonyl transposition with retention of a hydroxyl group at the original carbonyl site, these workers then prepared 275. Oxidation of this intermediate followed by end acetylation afforded 276. When this enone was irradiated... 

A 1,2-carbonyl transposition sequence based on the Woodward dithioacetalisa-tion reaction was used to relocate a carbonyl group in 95.1 [Scheme 2.95] to the adjacent position in 95 6.190 A total of 6 steps were required in which the key step was the dithioacetalisation of the a-hydroxymethylene derivative 95 2. After reduction of the carbonyl group, the dithiane was hydrolysed to the a-acetoxy ketone whence dissolving metal reduction removed the acetate function. 

Montuiy and Goie have developed a 1,2-ketone transposition method (Scheme 22). Baeyer-Villiger oxidation of conjugated ketone (71) afforded an enol acetate and subsequent hydrolysis revealed a carbonyl group, one carbon removed from the original position. 

In 1,2-alkylative carbonyl transpositions where the carbonyl group moves forward into the newly added fragement, e. g. 63 - 64, the reagent behaves as an acyl anion equivalent. We have seen one example of this in the synthesis of the occidentalol intermediate 8. Phosphine oxides with OR or SR substituents on the a-carbon 65 are ideal reagents for this process as the Horner-Wittig reaction gives vinyl compounds which can be hydrolysed to 64. 

The next steps of the synthesis, which formally involves a 1,2-carbonyl transposition from C(3) to C(2) and its conversion to the desired endo-N group, followed by a Mannich condensation, are outlined in Schemes 13.2.4 -13.2.6. 

Ikegami has devised an interesting approach based upon 1,3-cyclooctadiene monoepoxide as starting material (Scheme LX) Transannular cyclization, Sharpless epoxidation, and silylation leads to 638 which is opened with reasonable regioselec-tivity upon reaction with l,3-bis(methylthio)allyllithium. Once aldehyde 639 had been accessed, -amyllithium addition was found to be stereoselective, perhaps because of the location of the te -butyldimethylsilyloxy group. Nevertheless, 640 is ultimately produced in low overall yield. This situation is rectified in part by the initial formation of 641 and eventual decarboxylative elimination of 642 to arrive at 643. An additional improvement has appeared in the form of a 1,2-carbonyl transposition sequence which successfully transforms 641 into 644... 

Ikegami s successful synthesis of racemic 720 materialized by initial conversion of 701 to 725 via a 1,2-carbonyl transposition sequence (Scheme LXXVIII) Treatment of 725 with methoxycarbene, deprotection, and oxidation provided 72 6. Acid-promoted cyclopropane ring cleavage and added functional group manipulation led to 727 which could be allylated stereoselectively. The tricyclic enone 724 was subsequently produced conventionally. 

In the first of these syntheses, described by Fujimoto and coworkers (Scheme 32) [42], the acetoxy derivative 248, prepared from tetrahydrosantonin 3b, afforded ketoacetate 249 on treatment with tetramethyl ammonium acetate via a 1,2-carbonyl transposition reaction. Irradiation of this compound in the presence of HgO/l2 led to the oxidation of the C(14) methyl group of compound 250 to give compound 251,... 

---