Enol phosphates 1,2-addition reactions

It is conceptually easier to consider initially the aldol reaction rather than the reverse aldol reaction. This involves generating an enolate anion from the dihydroxyacetone phosphate by removing a proton from the position a to the ketone group. This enolate anion then behaves as a nucleophile towards the aldehyde group of glyceraldehyde 3-phosphate, and an addition reaction occurs, which is completed by abstraction of a proton, typically from solvent. In the reverse reaction, the leaving group would be the enolate anion of dihydroxyacetone phosphate. 

The same SN2 addition is also observed in reactions of the cuprate with the silyl enol ether or the enol phosphate of the epoxy ketone. This regiosclectivity is applicable to five- and six-membered ring systems and, to a lesser extent, to acyclic systems, which are generally less reactive. 

In the third pathway for the formation of 3-deoxyulosonic acids, enol pyruvate phosphate and an aldose phosphate are condensed, yielding orthophosphate and a 3-deoxyulosonic acid phosphate. In addition to formation of 3-deoxy-n-araInno-heptulosonic acid 7-phosphate, another example of this type of reaction is the formation of a 3-deoxyoctulosonic acid 8-phosphate (probably 3-deoxy-D-jfJMCo-octulosonic acid) from enolp3Tmvate phosphate and D-arabinose 5-phosphate. These reactions, unlike those involving pjrruvate, proceed completely to the right and have, so far, not been reversed. 

Reactions of cycloalkadiene monoepoxides have received considerable attention. In general, cyanocu-prates have provided better Sn2 selectivity than lithium homocuprates, and the alternative Sn2 reaction is more competitive with vinyl- or phenyl-cuprates than with alkylcuprate reagents. Reactions of cy-clopentadiene monoepoxides with cyanocuprates have found application in prostaglandin synthesis. Effective electrophilic a -alkylation of cyclic enones can be accomplished by Sn2 cuprate addition to the corresponding epoxy enolate, enol phosphate or silyl enol ether. ... 

Fig. 6.40. Eschenmoser s interpretation of glycolaldehyde phosphate aldomerisation reactions [37] It is generally appreciated... that the BUrgi-Dunitz trajectory... for nucleophilic addition to C = 0 groups must be taken into account as steric interactions between reaction center substituents are evaluated. The drawings in (this figure) remind the reader why. While it can be difficult to weigh the contributions of the four relevant interactions for an aldehyde/ketone-enolate pair, the problem for the case of an aldehyde/aldehyde-enolate pair turns out to have a unique solution the one indicated in (this figure), where none of the interacting substituents is juxtaposed with a non-H-atom partner ...

Thiol is converted to a nucleophilic thiolate anion, which reacts with an epoxide to give a ring-opened sulfide, in the presence of TMG (1) [74]. A carbapenem antibiotic carrying a sulfide function was synthesized practically by the addition-ehmination reactions of a thiol to the enol phosphate of p-keto ester in the presence of TMG (1) as a key step [75] (Scheme 4.27). 

Convenient new routes to tricyclo[4,1,0,0 ]hept-3-ene and its derivatives have been disclosed. Acetone-sensitized irradiation of bicyclo[3,2,0]hept-6-en-2-one affords the ketone (624), whose enol phosphate is reduced by lithium-ammonia to give the parent alkene (625). " A second route is also described, starting from the 7,7-di-bromonorcarane derivatives (626) and (627). Reaction of (626) with methyl-lithium in ether at 0°C afforded a 3 1 mixture of the tricycloheptenes (628) and (629) similar reaction of (627) gave (630 40%), but reactions of the parent dibromide were unsuccessful. Catalytic Ag ion causes the rearrangement of (628) and (629) to, respectively, 3-methyl- and 1-methyl-cycloheptatriene. Initial Ag" attack at the least hindered edge bond is implicated. Attempted preparation of the tetrahedrane dimer (631) by the addition of dibromocarbene to homobenzvalene followed by treatment of the adduct so obtained with excess methyl-lithium in ether at 0°C afforded instead 5-ethynyl-cyclohexa-1,3-diene. 

Using the Curtin-Hammett Principle to Predict the Stereochemistry of an Addition Reaction 379 Applying the Principle of Microscopic Reversibility to Phosphate Ester Chemistry 380 Kinetic vs. Thermodynamic Enolates 382 Molecularity vs. Mechanism. Cyclization Reactions and Effective Mol a ri ty 384... 

Coupling with Allylic and Enol Phosphates. The reagent converts allylic phosphates into allylsUanes (eq 3). Reaction with (2-vinyl-1,1-cyclopropanedicarboxylate gives the 1,7-homo-conjugate addition product (eq 4). In the presence of a Pd catalyst, PhMc2SiAlEt2 converts enol phosphates into vinylsilanes (eq 5). Higher yields are usually obtained with PhMe2SiMgMe. 

A nickel catalyst allows reaction between (1) and an enol phosphate, silyl enol ether, or substituted dihydrofurans and dihydropyrans to afford allylsilanes. Additional functionality can be tolerated in the substrate. ... 

Without additional reagents Perkow reaction Enol phosphates from [Pg.343]

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