1.3- Enone transposition

Enone transposition. A new method for this transposition depends on the regio- and stereoselectivity of addition of C6HsSeCI to allylic alcohols. An example is shown in equation (I). 

The high regioselectivity observed in the addition of phenylselenyl chloride to allylic alcohols is the cornerstone of a 1,3-enone transposition (Scheme 36). " The methodology effects both simple and alkylative transpositions in 40—60% overall yield in both cyclic and acyclic systems. 

The cyclobutane (149) is a 2-lithio-1,3-diene equivalent. Reaction with electrophiles (E" ) followed by oxidation and thermolysis gives 2-substituted 1,3-dienes. Lithium enolates [R C(OLi)=CHR ] will add to vinylselenoxides [R CH=CHSe(0)Ar] to provide a route to acylcyclopropanes U50), and Scheme 27 describes a 1,3-enone transposition that depends upon the easy introduction and oxidative removal of the phenylseleno group. ... 

Ketone rac-13 was transformed into the corresponding silylenolether and by Pd(II)-mediated Saegusa oxidation [14] into a, -unsaturated ketone rac-14. By alkylative enone transposition comprising methyl lithium addition and pyridinium chlorochromate (PCC) oxidation [15], rac-14 was finally converted into the racemic photo cycloaddition precursor rac-6. In conclusion, the bicyclic irradiation precursor rac-6 was synthesized in a straightforward manner from simple 1,5-cyclooctadiene (11) in nine steps and with an overall yield of 21%. 

The introduction of the double bond of rac-14 was performed by conversion of rac-13 into its a-phenylselenide, subsequent peroxide oxidation, and elimination. Following the synthesis reported by Mehta and Srinivas, an alkylative enone transposition was used as the last step towards irradiation... 

The examples shown in Scheme 2 illustrate (a) a method for RsC— Br -> RzO or R3C—OH and (b) dialkyladve enone transposition as shown in essence in equation (2). The sequence R2CH—Cl R2CH—Sn -> R20 was crucial in a synthesis of the troponoid nezukone (1), as other methods of functionalizing the R2CH—Cl system in this ring failed (equation 3). The dialkylative enone transposition (equation 2) was illustrated by a short synthesis of dihydrojasmone (equation 4). ... 

Grieco, P.A., Nishizawa, M., and Marisovic, N. 1976. Remote double bond migration via rhodium catalysis A novel enone transposition. JAm Chem Soc 98, 7102-7104. 

New methods for die 1,2-transposition and alkylative 1,2-transposidon of carbonyl groups via vinylsi-lanes or vinyl sulfides have been explored which are based on the Shapiro reaction as the key reaction (Schemes 14 and IS). " These methodologies have been further extended to regiocontrolled enone transpositions. ... 

Trialkylstannyl-lithium reacts with secondary alkyl halides (substitution) and with a/S-unsaturated carbonyl compounds (conjugate addition) to give alkyl tin derivatives which may be oxidized with chromic anhydride in pyridine to give a saturated ketone. Applying the procedure to a cycloalkenone, an efficient dialkyl-ative enone transposition can be realized (Scheme 68). ... 

A method for the conversion of tosylhydrazones of a, -enones to transposed allylic sulphides has been described. Combining this with the known methods for regiospecific conversion of allylic thioethers to enones produces a controlled enone transposition with a 1,2-carbonyl shift (Scheme 20). 

A novel enone transposition has been described by Grieco et al. an olefinic double bond can be caused to migrate about a six- or eight-membered carbocyclic ring to attain the most stable arrangement using a rhodium catalyst [i.e. (40)->... 

This section contains alkylations of ketones and protected ketones, ketone transpositions and annulations, ring expansions and ring openings and dimerizations. Conjugate reductions and Michael alkylations of enone are listed in Section 74 (Alkyls from Alkenes). 

This same concept applies to spiroannulations of six membered rings and is illustrated in a synthesis of acorenone B 155 as outlined in Scheme 547). The notion of alkylative carbonyl transposition permits the spiro enone 156 to become a logical intermediate. The standard analysis by a retro-aldol process translates the spiro ring system of acorenone B into a geminal alkylation problem as revealed by... 

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. 

Sometimes, chromate esters from secondary a]]vi-transposition rather than direct oxidation, the rLI" ° l0ls Suffer chromate ester can either produce epoxidation of the iv transPosed oxidation yielding a transposed enone.84 a ene or suffer... 

The initially formed allylic chromate ester equilibrates with an isomeric chromate ester Both allylic chromate esters produce the epoxidation of the alkene. The resulting epoxy alcohols are oxidized to epoxy ketones A and B in a 5 3 ratio. Starting from an equatorial alcohol instead of an axial one, an uneventful oxidation to enone occurs without transposition. 

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