Diastereomers in excess

Regioselectivc endo deprotonation and alkylation of 4,5-dihydroisoxazoles proceeds under asymmetric induction controlled by the substituent(s) in position 5. These substituents shield one of the diastereotopic faces of the 4,5-dihydroisoxazole, such that alkylation provides the trans-diastereomers in excess (see Table 1). 

Transfer of carbene 3a from 19 to a variety of alkenes and cycloalkenes has been achieved under catalysis by copper(I) chloride74,79 - 82. However, with the exception of cyclohexene69,70 (72% yield), only moderate yields could be obtained. In all cases, the cyclopropanation was stereospecific with respect to the double bond configuration of the alkene and gave the sterically less crowded cyclopropane diastereomer in excess. As in the photochemical cyclopropanation, the formal carbene dimer trans-1,2-bis(trimethylsilyl)ethene is often formed as the major by-product. Cyclopropanation of fraws-but-2-ene with 19 with copper(II) chloride as catalyst was found to be even less... 

Whereas primary aUyl alcohols may be converted to the extent of 100%, for secondary alcohols, kinetic resolution is used to obtain one diastereomer in excess. The J. T. Baker Company harked back to the original work of Sharpless [194] and developed from it an industrial process for the production of (+)-dis-parlure. 

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See also in sourсe #XX -- [ ]

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