The New skew and the Established cis and gem Regioselectivities in the Ene Reaction of Trisubstituted Olefins:  Comparison of the Singlet Oxygen, Triazolinedione, and Nitrosoarene Enophiles

Ene Reactions of Nitrosocarbonyl Intermediates with Trisubstituted Cycloalkenes: “Cis Effect” and Steric and Conformational Factors Drive the Selectivity

“…8,9 Typically, the “cis effect” occurs in singlet oxygen 1 O 2 ene reactions and refers to the neat preference of 1 O 2 for the abstraction of the twix and lone allylic hydrogens from the more congested side of an olefin (Figure 1, see inset). 11 Other enophiles display different selectivities: aromatic nitroso compounds (Ar–NOs) 12 and triazolinediones (TADs) 13 favor the M “end” selectivity but differ in the “cis” preferences. The Ar–NOs maintain some “cis” selectivity favoring the twix over the twin abstraction; on the other side, TADs do not discriminate between the two sites.…”

Organic Dye‐Photocatalyzed Acylnitroso Ene Reaction

“…We next turned our focus to nitroso ene reactions with tiglic acid derivatives (Table 3, entries 5–9). The products obtained provide access to α,β‐disubstituted amino acids, which have few direct synthetic methodologies 14. Poor yields were reported previously by using tiglic acid derivatives as the ene substrates because of the electron‐deficient double bonds 6.…”

Developments in Nitrosocarbonyl Chemistry: Mild Oxidation of N-Substituted Hydroxylamines Leads to New Discoveries

“…When trisubstituted olefins were employed, the nitrosocarbonyl enophiles preferred to approach with a skew geometry. 26 Hydrogen atom abstraction preferentially occurs from the twix position in all cases (31-33 and 39). Electron-deficient olefins also reacted, albeit with extended reaction times; amides, esters and carboxylic acids all proved to be viable nucleophiles for the nitrosocarbonyl ene reaction (34-36).…”

“…However, it is important to note that olefin geometry plays an important role in the intramolecular reaction: N-hydroxycarbamates bearing Z-olefins decompose under the reaction conditions. The reaction could be extended to include a number of hydroxylamines bearing common protecting groups that could be orthogonally deprotected, such as Boc, Cbz, Fmoc and Troc (25)(26)(27)(28). Additionally, a wide range of olefin substitution patterns were well tolerated, affording the allylic N-hydroxycarbamates in moderate to excellent yield (29, 30, 37 and 38).…”