Homoenolates dianion equivalents

Aldol-iype Condensation. Dimetalation of (R)-(+)-3-(p-tolylsulfinyl)propionic acid with Lithium Diisopropylamide produces a chiral homoenolate dianion equivalent which reacts with carbonyl compounds to afford p-sulfinyl-y-hydroxy acids these spontaneously cyclize to give the corresponding p-sulfinyl 7-lactones (eq 2) ... 

Homoenolate Dianion Equivalent. The intermediate in the reaction is believed to be an enol silane and/or enol titanate which gives the expected product with carbon electrophiles such as acetals (eq 3). ... 

Otherwise a-methoxy allyl sulfides have played the role of an a-methylenated acyl anion (Scheme 76, entry a) or a homoenolate dianion (Scheme 76, entry b) equivalent. 

We have developed a completely new synthesis of chiral aldols 12 by formal enantioselelective connection of a C-0 and a C-C bonding at the C3-position of a homoenolate dianion synthon 11 (Scheme 1). Because the natural polarity of the reactants is reversed twice the direct approach is not possible. Therefore we used the allyl amine 1 and enamine 2 as excellent synthesis equivalents of homoenolates, which can be silylated and alkylated, respectively (Scheme 2). 

Treatment of 3-stannylpropionamide with two equivalents of butyllithium at low temperature (—78 °Q generates a similar dianionic homoenolate, which reacts with standard electrophiles Eq. (46) [43], It is interesting to note that the propionate moiety rather than the butyl groups is selectively cleaved off the tin in the tin-lithium exchange. 

In place of a Grignard reagent, several homoenolate equivalents have also been employed. Kempt 1 7 reported the titanium-mediated addition of /V-alkylmethylacrylamide dianions to N-protected a-amino aldehydes (Scheme 8). Pyrolytic cyclization affords a 3-methylenetetrahydrofuran-2-one and the side chain of C3 is appended via conjugate addition. The resulting lactone can be converted into the 1-hydroxyethylene dipeptide by hydrolysis. The stereochemistry of the C6 atom is the same as that of the a-amino aldehyde. However, the stereoselectivities of the reactions regarding the C3 and C5 atoms are unsatisfactory. 

Taylor, E.C., and Davies, H.M.L., Rhodium(II) acetate-catalyzed reaction of ethyl 2-diazo-3-oxopent-4-enoates. Simple routes to 4-aryl-2-hydroxy-l-naphthoates and P,y-iinsaliiralcd esters. The dianion of ethyl 4-(diethylphosphono)acetoacetate as a propionate homoenolate equivalent, Tetrahedron Lett., 24, 5453. 1983. 

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