76807-01-7Relevant articles and documents
Electrophilic substitution with allylic rearrangement (SE′) stereochemistry of trifluoroacetolysis of some cyclohex-2-enylmetal compounds
Wickham, Geoffrey,Young, David,Kitching, William
, p. 1187 - 1195 (2008/10/08)
A range of (4-alkylcyclohex-2-enyl)-, (5-alkylcyclohex-2-enyl)-, and (6-alkylcyclohex-2-enyl)silanes, (4-alkylcyclohex-2-enyl)-, (5-alkylcyclohex-2-enyl)-, and (6-alkylcyclohex-2-enyl)germanes, and (4-alkyl-cyclohex-2-enyl)-, (5-alkylcyclohex-2-enyl)-, and (6-alkylcyclohex-2-enyl)stannanes were cleaved to the cycloalkene (and R3MX) with trifluoroacetic acid-d in various solvents. Complete allylic rearrangement (γ-attack) was observed, and the preferred direction of delivery of the electrophile (formally D+) to the γ-carbon of the allylic triad was determined by detailed 1H, 13C, and 2H NMR analyses of the derived dibromides of the various alkyl-substituted cyclohexenes or by direct 2H NMR analysis and comparisons with 2H-substituted alkylcyclohexenes of established relative configurations. A highly preferred γ-anti mode of acidolysis is established for all systems, except for the trans-4-tert-butylcyclohex-2-enyl derivatives, such exception being ascribed to steric impedance of electrophile approach, promoting syn attack. Thus, overall, highly γ-regioselective and anti-stereoselective substitutions (SE′) are observed.
Alkylation of Allylic Derivatives. On the Regio- and Stereochemistry of Alkylation of Allylic Alcohols by the Murahashi Method
Goering, Harlan L.,Kantner, Steven S.
, p. 2144 - 2148 (2007/10/02)
Direct alkylation of allylic alcohols by the Murahashi method has been reinvestigated.This four-step, one-pot process evidently involves formation of the lithium (allyloxy)alkylcuprate (2) followed by the reaction with (methylphenylamino)triphenylphosphonium iodide (1a) or the corresponding tributylphosphonium iodide (1b).Contrary to earlier implications, the regiospecific and stereospecific anti γ-alkylation is independent of which aminophosphonium reagent is used.Presumably the final step involves alkylation of the (allyloxy)phosphonium ion (3) by LiCu(R)(N(CH3)Ph).This mixed cuprate also alkylates allylic carboxylates with about the same regio- and stereochemistry as for the Murahashi direct alkylation of the corresponding allylic alcohol.A general mechanism is presented that suggests that the regiochemistry of alkylation of allylic derivatives depends on the nature of the ancillary ligand in the alkylating cuprate.
