Alkenylation conjugate enone

Alkylations with conjugated enones carrying a leaving group at the P-position proceed smoothly, producing mono-alkenylated pyrroles. ... 

With glyceraldehyde-derived enones and enoates, it has been found that addition of aryl or alkenyl copper reagents is almost independent of the enone geometry [24, 25]. In agreement with the modified Felkin-Anh model, Z enoates usually provide high levels of anti selectivity (Scheme 6.11). Hence, the Z derivative 64 reacted with complete stereochemical control, whereas the -enoate 64 gave a lower selectivity of 4 1 in favor of the anti-conjugate adduct [25]. 

Enantioselective conjugate addition can also be carried out with cyclic enones. Shuichi Oi and Yoshio Inoue of Tohoku University in Sendai report (Tetrahedron Lett. 2004, 45, 5051) that a BINAP complex of Rh catalyzes the enantioselective conjugate addition of alkenyl Zr species such as 5, to give 7 in high enantiomeric excess. Alkenyl Zr species such as 5 are readily prepared by hydridozirconation of alkynes. It is particularly important that addition of TMS-C1 to the reaction mixture at the end of the conjugate addition leads cleanly to the enol ether 6. 

Irrespective of the stereochemistry of the ot,p-enones, lithium alkenyltrialkylalanates, e.g. (28) and (29), obtainable by treatment of alkenylalanes with methyllithium (or n-butyllithium), are also excellent 1,4-conjugate alkenyl transfer reagents. The cornerstone of a general prostaglandin synthesis, as exemplified in Scheme 6, employs the alanate conjugate addition process exclusively.13... 

Indium metal reduces the terminal triple bond of aryl propargyl ethers, amines, and esters in aqueous ethanol to produce the corresponding alkenyl compounds (Tab. 8.23) [119]. Indium metal in aqueous ethanohc ammonium chloride reduces the carbon-carbon double bond of activated conjugated alkenes such as a,a-dicya-no olefins, /faryleriories, and enone esters (Scheme 8.88) [120]. 

Unsubstituted vinyl-lithium and vinyl Grignard 14 reagents can be made directly from the halide by oxidative insertion of Li(0) and Mg(0). Vinyl-lithium is available as a 2M solution in THF from Alfa and vinyl magnesium bromide, which must be prepared in THF, is available in THF from Aldrich. These are quite stable o-complexes because alkenyl anions are more stable than saturated alkyl anions. They add as nucleophiles to carbonyl groups, e.g. cyclobutanone to give 15 and prefer direct to conjugate addition with enones to give e.g. 13. We have already used them in enone synthesis (chapter 5). 

Active manganese. A convenient procedure for the preparation consists of reduction of Li2MnCl4 with Li /2-phenylpyridine in THF at room temperature. It converts. irganohalogen compounds into species reactive toward PhCOCl, enones and conjugated esters, and alkenyl halides. 

Alkylations. Allylation of aldehydes with the stable allyltrifluoroborate reagent proceeds at low temperatures by using BF3-OEt2 as catalyst. Crotylation is performed analogously. In the presence of (acac)Rh(CO)2 and a phosphine the alkenyl- and aryltrifluoroborates add to aldehydes and enones, the latter in a conjugate fashion. ... 

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