Molecular rearrangements of superelectrophiles

• Douglas A. Klumpp

Beilstein J. Org. Chem. 2011, 7, 346–363, doi:10.3762/bjoc.7.45

• superelectrophile, which undergoes rearrangement via the protonated cyclopropyl derivative 49. Final reaction steps include a hydride shift and deprotonations to give 50. Jacquesy and coworkers [24] have investigated the chemistry of polycyclic ketones in HF-SbF5-CCl4, a powerful reagent combination for

• hydride migration in 70 to give dication 71. This step should be favorable because it increases the distance between charge centers. Although a hydride shift is the most direct route from 70 to 71, this isomerization may also occur through deprotonation and reprotonation steps. As noted by the authors of

• -diprotonated species 93. Migration of the methyl group leads to separation of the charge centers and the formation of dication 94. Theoretical calculations show that hydride shift for the dications (94 → 95) is energetically unfavorable, presumably due to the closer proximity of the charges. In the final steps

Addition of lithiated enol ethers to nitrones and subsequent Lewis acid induced cyclizations to enantiopure 3,6-dihydro-2H-pyrans – an approach to carbohydrate mimetics

• Fabian Pfrengle and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2010, 6, No. 75, doi:10.3762/bjoc.6.75

•  10). Sodium azide presumably acts as base to initiate the reaction by deprotonation of the hydroxylamine moiety. A hydride shift from the benzylic position to the 3-position of the pyran ring produces the nitrone moiety of 21 and simultaneously displaces the axially positioned bromo substituent by an

A review of new developments in the Friedel–Crafts alkylation – From green chemistry to asymmetric catalysis

• Magnus Rueping and
• Boris J. Nachtsheim

Beilstein J. Org. Chem. 2010, 6, No. 6, doi:10.3762/bjoc.6.6

• intermediate which subsequently undergoes an intramolecular [1,3]- or [1,5]-hydride shift resulting in the desired diarylmethanes 9 in good yields. Electron donating and electron withdrawing functional groups of aldehyde moiety are tolerated in this reductive Friedel–Crafts alkylation procedure. However, there

• is no clear correlation between the electron deficiency of the arenecarbaldehyde and the reaction yield [4]. Further mechanistic investigations were performed with 1,3-propanediol-1,1,3,3-d4 in order to provide more information about the observed hydride shift. Indeed deuterium was incorporated into

Diastereoselective functionalisation of benzo-annulated bicyclic sultams: Application for the synthesis of cis-2,4-diarylpyrrolidines

• Susan Kelleher,
• Pierre-Yves Quesne and
• Paul Evans

Beilstein J. Org. Chem. 2009, 5, No. 69, doi:10.3762/bjoc.5.69

• carbocation rearrangement takes place faster than any nucleophilic interception of species 21 and 22. (A hydride shift from the bridging CH2 to carbocation 21 was also considered; however, based on the regioselective formation of compound 19b this mechanism was discounted.) The remarkable contrasting

The tert- amino effect in heterocyclic chemistry: Synthesis of new fused pyrazolinoquinolizine and 1,4-oxazinopyrazoline derivatives

• Dipak Prajapati and
• Kalyan Jyoti Borah

Beilstein J. Org. Chem. 2007, 3, No. 43, doi:10.1186/1860-5397-3-43

• undergoing a 1,5-(4 → 5) hydride shift prior to cyclization to yield a 6-membered ring product 6 (Scheme 2). This is in contrast to an earlier report by Sandhu et al to obtain pyrrolo [2,3-d]pyrimidines from 6-tert-amino-substituted uracils and dimethyl acetylenedicarboxylate.[32] However, further work is in