Stereoselective γ-cis-vinylic metallation of tertiary allylic alcohols

Abstract

Tertiary allylic alcohols are converted by BunLi-tetramethylethylenediamine into the y-cis-vinyl-lithium derivatives which can be alkylated in moderate yields.

Probing the Mechanism of 1,4-Conjugate Elimination Reactions Catalyzed by Terpene Synthases

“…8a We have also probed the intermediacy of trans- nerolidyl diphosphate ( 12 ) in the catalytic cycle of EBFS with (2Z, 6E)-FDP (cis- 3 ) and (3 RS)-trans -NDP ( 12 ), which were prepared as indicated previously. 16b,18,19 …”

“…19 GC-MS analysis reveled that EBFS converted cis - 3 (and 12 ) almost exclusively and with high efficiency to ( E )-β-farnesene (93%) suggesting that the reactions for both FDP isomers proceed via a common intermediate arising from the plausible collapse of either cis- farnesyl or trans- farnesyl cation to NDP ( 12 ). Indeed, (3 RS )-(1 Z )- trans -[1- 3 H 1 ]NDP, prepared by stereoselective γ- cis -vinylic metallation 26 of racemic trans nerolidol, 27 displayed a turnover number ( k cat = 0.023 ± 0.001 s −1 ) 28 similar to that measured for FDP ( k cat = 0.028 ± 0.002 s −1 ) in good agreement with a reaction along pathway c (Scheme 1). It is noteworthy that racemic trans -NDP was used in the kinetic analysis and hence the Michaelis constant measured for racemic trans -[1- 3 H 1 ]NDP ( K M = 25.0 ± 4.2 μM, Table 1) is not easily compared with that measured for 3 .…”

Iron-Catalyzed Cross-Coupling of Unactivated Secondary Alkyl Thio Ethers and Sulfones with Aryl Grignard Reagents

“…Moreover, allylic sulfones have also served as competent electrophiles in copper- 33 and iron-catalyzed 34 displacements with Grignard reagents (Scheme 2, Eq. 3), nickel- 35 and palladium-catalyzed 36 alkylations with stabilized enolates, Lewis acid-mediated substitutions with organoalanes, 37 and alkylations with lithium dialkylcuprates. 38 Recently, Li and co-workers described an isolated example of a nickel-catalyzed cross-coupling of a benzylic sulfone with MeMgBr (Scheme 2, Eq.…”

Palladium-catalyzed desulfinylative C–C allylation of Grignard reagents and enolates using allylsulfonyl chlorides and esters

“…In the case of Pd(PPh 3 ) 4 -catalyzed reactions it seems that the (crotyl)Pd(ligand) intermediate does not make any great difference for the Nu insertion into the non-substituted (less steric hindrance) and the methyl substituted center of the (allyl)palladium moiety. For more than 30 years it has been known that the regioselectivity of allylic alkylation, [86][87][88][89][90][91][92][93][94][95] allylic vinylation, [96][97][98] and allylic arylation [99][100][101][102] depends on the nature of the catalyst. Although many more experiments should be carried out to approach a mechanistic interpretation of our results, we propose at this stage that (allyl)palladium intermediates 7 and 8 are formed by reactions of 2c or 2d with PdCl 2 (PhCN) 2 and Pd(PPh 3 ) 4 , respectively (Scheme 3).…”