Hydride shifts diastereoselectivity

Scheme 18 Diastereoselectivities of the Lewis acid catalyzed reactions of benz-hydryl chloride with (it)- and (Z)-2-butene. Further products, arising from hydride shifts, are described in Scheme 21. (From Ref. 19.)...

Diazoalkanes undergo smooth 1,3-dipolar cycloaddition. For additions to simple alkenes, this is presumably an electrophilic process. In the example illustrated, the overall process of electrocyclization of (142) followed by hydride shift proceeds with remarkable diastereoselectivity (equation 57). ... 

Indium trichloride induces rearrangement of aryl-substituted epoxides to the respective aryl-substituted acetaldehydes via an exclusive hydride shift As phenyl group migration occurs more readily than hydride migration, stilbene oxide is converted to diphenylacetaldehyde (Scheme 8.140) [184]. N-Tosyl aziridines react smoothly with carboxylic acids in the presence of a catalytic amount of indium triflate to afford the corresponding -aminoacetates and benzoates (Scheme 8.141) [185]. Indium trichloride and indium bromide catalyze regio- and diastereoselective azidolysis, bromolysis, and iodolysis of a, -epoxycarboxylates in water (Scheme 8.142) [186]. 

Scandium triflate catalyzed the intramolecular redox reaction from yne-enones to ring-fused tetrahydroquinolines (eq 28). This Lewis acid-catalyzed intramolecular redox domino reaction occurs via domino 1,5-hydride shift and cycUzation to afford tetrahydroquinolines in moderate to excellent yields and with high diastereoselectivity. A similar Sc(OTf)3-catalyzed tandem 1,5-hydride transfer cyclization process was applied in the construction of 3-amino-3-carboxy-tetrahydroquinoline derivatives (eq 29). ... 

Scheme 23) [107], which produced spiropyrazolo-terahydroquinoline derivatives 69 in good to high yields with good to excellent diastereoselectivities (up to 95 % yield, >95 5 dr). The strong Lewis acid, i.e., ZnCl2, could not only facilitate the formation of enone I and enolate II but also increase the electrophilicity of enone by chelation of the carbonyl of enone to promote 1,5-hydride shift. 

Akiyama et al. reported a Brpnsted acid-catalyzed synthesis of 3-aryl-1-trifluoromethyltetrahydroisoquinolines 230 and 230 by a benzylic [l,5]-hydride shift-mediated C-H bond functionalization (Scheme 87) [142], which features the diastereo-divergent synthesis of 3-aryl-l-trifluoromethyltetrahydroisoquinolines 230 and 230 by tuning the substiments on nitrogen atom. The trifluoromethylketimine derived from para-anisidine and activated by Tf2NH served as hydride acceptor and the substituents on ketimines had dramatic impacts on the diastereoselectivities cis-product 230 could be furnished as major product when R was PMP group, whereas the diastereoselectivity was reversed with R as hydrogen. 

Scheme 8 anri-Diastereo- and enantioselective siloxy-crotylation in the transfer hydrogenative coupling of primary alcohols with alkynes via hydride-shift enabled ji-aUyl formation. Yields are of material isolated by flash chromatography on silica gel. Diastereoselectivity was determined through NMR analysis of crude... 

We have delineated the mechanism of this new diastereoselective reaction that involves an initial IMDA, followed by a double-bond isomerization, and finally 1,5-dienyl hydride shift [37]. The racemic tricycle carboxyhc acid was resolved via (S)-2-phenylglycinamide and converted to the aldehyde 46 that served as a convenient intermediate for analog synthesis. 

The cyclopropanation reaction of styrene with 2,4-dimethyl-3-pentyl a-diazopropionate by catalysis with 1 mol % of Rh2(5-TBPTTL)4 at —78 °C provides trans-cyclopropane in high yield with virtually complete diastereoselectivity and 86% ee (eq 5). The reaction can be carried out without slow addition of the diazo reagent, in which no signs of alkene product derived from a 1,2-hydride shift or dimeric products were observed. 

A relay catalytic hydroamination/redox reaction for the synthesis of cyclic aminals 83 from tertiary amine-substituted 3-en-l-yne derivatives 81 and various aniline derivatives 82 was recently developed by Gong and coworkers (Scheme 12.40) [43]. The gold carbene complex [(IPrlAuNTfj] and TfOH were found to be optimal cocatalysts for this cascade reaction. In their preliminary studies, the authors found that this reaction could be carried out in a highly enantioselective manner, despite that 2 equiv. of an expensive chiral phosphoric acid are required. Interestingly, the diastereoselectivity for a particular substrate appears to be independent of the catalyst or ee. This suggests that the enantioselectivity may result from the ring-closure step, rather than the hydride shift step. 

Hegedus and coworkers have shown that the reaction of optically active a-oxazolidinonylallenylstannanes (50) with oxiranes, in the presence of BF3 OEt2, produces the p-hydroxypropargylamines (51) with high syn diastereoselectivity (Equation 32) [33]. Here, the Lewis acid is responsible for the rearrangement of the oxiranes to the corresponding aldehydes via alkyl, aryl or a hydride shift. 

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