Ring diasteroselective

Only tethered terminal olefins are reactive, and ring junctures are always formed by coupling to the internal carbon of the multiple bond. If an asymmetric center is present in the tether, the reaction proceeds with high diasteroselectivity. Alkenes with substituents a to the double bond favor trans product formation, whereas fi substituents lead to cis products. 

Other C-electrophiles besides iminium salts and carbonyl compounds have not yet extensively been tested for C-C-forming cyclopropane ring cleavage. However, whereas acyl or tertiary alkyl halides do not give addition products, benzaldimine at least provides the expected secondary amine 194 with good yield and diasteroselectivity 61). 

Reaction of furyllithium (60) with L-threonine derived lithium salt 61 afforded the expected ketone 62 in 30% yield. Reduction of 62, using lithium aluminium hydride, gave two alcohols (63 and 64) in a 3 1 ratio. In both carbinols (63 and 64) the oxazoline ring was opened by acid hydrolysis to give the N-benzoyl derivatives 65 and 66, respectively. Alcohol 66 can be used in the synthesis of lincosamine enantiomer, but unfortunately this approach has limited preparative value because of the low yield obtained in the condensation step and, on the other hand, opposite diasteroselectivity obtained in the reduction reaction. 

An iodine-catalysed ring-opening 5 2 reaction of 2-substituted epoxides by 2-phenyl-l,3-oxazolan-5-one in the ionic liquid [BmimjOH forms 3-(A-substituted)aminofuran-2-ones in yields ranging from 84 to 95% with a diasteroselectivity of 95-98%P [BmimjOH was the best of five ionic liquid solvents tested and increasing the size of the cation did not affect the yield. A tentative multistep mechanism is presented. 

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