Enones transposition

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... 

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 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). 

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. ... 

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)->... 

---