Hydroxylamine conjugated enones

For those who are familiar with natural products chemistry it will be easy to recognize in structure I the main features of a-Santonin (III). This was a heavily investigated compound during the 1950s and 1960s, especially its photochemistry. The particular functionality that attracted so much attention is the cross-conjugated enone moiety. It is this function in fact that warranted the construction of the starting compound I by way of a double Michael-type addition of hydroxylamine. ... 

The bifunctional heterobimetalhc complexes developed by Shibasaki and coworkers, which have been used to effect high ees in a variety of conjugate additions discussed in this chapter, are also effective in the conjugate additions of hydroxylamines to enones and up to 99% ee has been obtained using the ytterbium lithium binaphthoxide YListrisjbinaphthoxide) (YLB). °... 

Selenols are capable of acting as useful reducing agents. Thus, benzeneselenol (PhSeH) reduces imines to amines, aldoximes to hydroxylamines, and selectively reduces the C=C double bond in conjugated enones the last two transformations are photochemically induced. Similarly, hydrogen selenide (H3Se) photoreduces ketones and aldehydes to alcohols. ... 

Alternatively, Shibata and coworkers first realized the catalytic enantioselective synthesis of trifluoromethyl-substituted 2-isoxazolines 69 in 2010 by developing a cinchona-alkaloid-catalyzed asymmetric conjugate addition/cyclization/dehydration cascade reaction with hydroxylamines 67 and enones 68 (Scheme 2.19). A wide range of substrates could be employed in this reaction to give the desired cyclized products with excellent enantioselectivities [33]. 

Reaction of the enone (60) with a variety of IV-substituted hydroxylamines gave the conjugate addition products (61), whereas the analogous reaction with 0-methylhydroxylamine gave a mixture of oximino-derivatives (62) and (63) (Scheme 6). Reduction of uloses (61) with sodium borohydride gave predominantly products with the D-araWno-configuration the e.s.r. spectroscopy of free radicals produced on spontaneous oxidation of such products is covered in Chapter 22. The condensation of... 

Shibata and coworkers [135] described the asymmetric phase-transfer catalytic synthesis of trifluoromethyl-substituted 2-isoxazolines 100 by an enantioselective conjugate addition of hydroxylamine to trifluoromethylated enones 99 and subsequent intramolecular formation of the imine, whereas Briere et al. [136] developed a facile method for the straightforward enantioselective synthesis of 3,5-diaryl pyrazoHnes 102 by phase-transfer-catalyzed conjugate addition of N-Boc-hydrazine... 

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