Stereoselective ring-opening reactions

Jacobsen etal, US Patent 6,262,278 (July 17, 2001) Assignee President and Fellows of Harvard College Utility Stereochemical Intermediates 

To a 0.2M solution of (R,R)-l,2-diaminocyclohexane (1 eq) dissolved in ethyl alcohol was added 3,5-di-t-butylsalicylaldehyde (2eq), the mixture refluxed 1 hour, and water added drop wise to the cooled yellow solution. The yellow precipitate was collected by filtration, washed with a small amount of 95% ethyl alcohol, and the product isolated in 90% to 97%. H- and i C-NMR data supplied. 

The product from Step 1 (2.29 mmol) was dissolved in THE, CrCl2 (2.52 mmol) added and the solution stirred under nitrogen 3 hours and 3 hours in air. The solution was diluted with 250 ml MTBE, washed 3 times apiece with 50 ml saturated NH4CI and brine, and the product isolated in 98% yield. H- and C-NMR data supplied. 

A flask was charged with the eatalyst from Step 2 (42 mg) and 1 ml diethyl ether. 1,2-Meso cyclopentane epoxide (0.060 mmol) was added and the mixture stirred 15 minutes at which time trimethylsilylazide (3.15 mmol) was added and the mixture stirred an addition 28 hours. Thereafter, the solution was concentrated and the residue filtered through a 10 ml plug of silica gel with 5% to 20% EtOAc/hexanes mixture. Desilylation was performed by dissolving the purified intermediate into 5 ml methyl alcohol to which was added (lS)-(+)-10-camphorsulfonic acid (0.15 mmol), the mixture stirred 30 minutes, purified by flash chromatography, and the product isolated in 80% yield, 94% ee. 

Both (R,R)- and (S,S)-l,2-bis(3,5-di-t-butylsalicylide-amino)cyclohexane intermediates were prepared using the appropriate diaminocyclohexane stereoisomers and are described. The catalytic intermediate, 2,2 -bis(3-t-butylsalicylideamino)-l,T-binaphthyl, (I), was also prepared by the author. 

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Wang, M.X., Wang, D.X., Zheng, Q.Y. et al. 2007. Nitrile biotransformations for the efficient synthesis of highly enantiopure l-arylaziridine-2-carboxylic acid derivatives and their stereoselective ring-opening reactions. Journal of Organic Chemistry, 72 2040-5. 

Under the same conditions as above, the unsymmetrical diphosphiranes (2o-p) undergo a regio-and stereoselective ring-opening reaction leading quantitatively to only trans 1,3-diphosphapropenes (Equation (19)) <89CC593>. 

Since this report in 1976, numerous studies of stereoselective ring opening reactions of variously substituted and enantioenriched VCPs have been reported. The formation of different stereoisomeric cyclopentene products suggests that die mechanism of the rearrangement might involve both the concerted and diradical pathways to different extents, depending upon the nature of substituents and their precise orientation on the corresponding... 

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