Homoenolates elimination reaction

The aryl- and heteroarylfluorosilanes 541 can be used for the preparation of the unsymmetrical ketones 542[400], Carbonylation of aryl triflate with the siloxycyclopropane 543 affords the 7-keto ester 545. In this reaction, transme-tallation of the siloxycyclopropane 543 with acylpalladium and ring opening generate Pd homoenolate as an intermediate 544 without undergoing elimination of/3-hydrogen[401],... 

The transmetallation of the siloxycyclopropane 751 with the aryl- or alke-nylpalladium 752 generates the Pd homoenolate 753. and subsequent reductive elimination gives the /3-aryl or alkenyl ketone 754[618]. It should be noted that the Pd homoenolate 753 generated in this reaction undergoes reductive elimination without d-elimination. 

The reaction of benzoyl chloride with (Me3Si)2 affords benzoyltrimethylsi-lane (878)[626,749,750]. Hexamethyldigermane behaves similarly. The siloxy-cyclopropane 879 forms the Pd homoenolate of a ketone and reacts with an acyl halide to form,880. The 1,4-diketone 881 is obtained by reductive elimination of 880 without undergoing elimination of /7-hydrogen[751]. 

Next to the cyclopropane formation, elimination represents the simplest type of a carbon-carbon bond formation in the homoenolates. Transition metal homoenolates readily eliminate a metal hydride unit to give a,p-unsaturated carbonyl compounds. Treatment of a mercurio ketone with palladium (II) chloride results in the formation of the enone presumably via a 3-palladio ketone (Eq. (24), Table 3) [8], The reaction can be carried out with catalytic amounts of palladium (II) by using CuCl2 as an oxidant. Isomerization of the initial exomethylene derivative to the more stable endo-olefin can efficiently be retarded by addition of triethylamine to the reaction mixture. 

Polladium(II) chloride or its phosphine complex smoothly reacts with siloxy-cyclopropane 1 to produce acrylic ester and a palladium mirror. This reaction probably involves the formation of a chloropalladium homoenolate followed by elimination of palladium hydridochloride (Eq. (56) [56]. 

Homoenolates generated from enals by NHC catalysis undergo annulation with chalcones in methanol to afford methyl hydroxycyclopentanecarboxylates stereose-lectively (Scheme 6.18). Construction of four contiguous stereocenters in a stereoselective manner is noteworthy. Mechanistically, the reaction undergoes events analogous to those in Scheme 6.16 until the intramolecular aldol reaction. Further, the catalyst gets eliminated by methanol to give the cyclopentanecarboxylates. Evidently, the interference of methanol before the intramolecular addition delivers the acyclic esters [22]. 

Transition metal cyclopropanolates underwent ring opening by P-carbon elimination to generate transition metal homoenolates. Palladium(ll)-catalyzed ring opening of substituted cyclopropanols predominantly occurred at the less substituted C-C bond to give conjugated enones (Scheme 2.31) [47]. When the reaction was performed under non-oxidative conditions, a mixture of unsaturated and saturated ketones was obtained [48]. 

---