Organolithium reagents regioselectivity

The regioselectivity of vinyloxiranes is interesting. Indeed, the ring opening of 3,4-epoxy-1-butene and 3,4-epoxy cyclohexene 88 with organolithium reagents... 

Some reports concerning the reaction of lithiated thioallylethers with oxiranes have been published. A slow reaction was observed with a terminal oxirane. However, with cyclopentadiene oxide, the reaction occured smoothly with an excellent regioselectivity in favor of the Sjv2 displacement in the ally lie position. Other examples involving sulfur, selenium and silicon stabilized organolithium reagents have been reported . 

The chiral Fischer-type chromium carbene complex of furan 28, shown in Scheme 14, participated in nucleophilic 1,4-addition with organolithium reagents followed hy alkylation in a regioselective and diastereoselective manner, creating a quaternary C-3 stereocenter in the 2,3-trisubstituted 2,3-dihydrofuran products after oxidative decom-plexation and reductive cleavage of the chiral auxiliary <2003CEJ5725>. 

The increased strain in oxabicyclo[2.2.1]heptenes such as 256b makes them more reactive toward organolithium reagents. The ring opening reactions occurred at lower temperatures and with higher regioselectivities, Eq. 187. 

Heterosubstituted allenes are versatile synthetic intermediates. Direct substitution of a heteroatom on the allene confers upon the system an electronic bias that allows the molecule to be deprotonated easily using an organolithium reagent, and also permits regioselective reaction with carbonyl compounds. 

Amide a-anions. The Boc-protected secondary amines are readily converted to a-lithio derivatives, which behave in the same way as other organolithium reagents. 7V-Boc-2-methyltetrahydro-l,3-oxazine undergoes regioselective deprotonation at C-4. ... 

The reactions of bis(diethylamino)carbenium salt 113 are summarized in Scheme 28 [65]. Nucleophilic additions of Grignard reagents, organolithium reagents, enolates, amides, thiolates, and phosphite take place regioselectively... 

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