Small molecules, such as trimethylamine N-oxide, interrupt intramolecular photoreactions of quinones by proton transfer and allow to convert a variety of quinones to spirocyclopropanes in a catalytic, diastereoselective, and atom-conserving manner.
Spirocyclopropanes promote axial orientation of adjacent groups on six-membered rings. The effect is due to steric and/or stereoelectronic effects, depending on the nature of the group, and is most significant for large or highly electronegative groups.
A diastereoselective [2 + 1] annulation reaction for synthesis of spirocyclopropane-fused 3-cyclohexenone derivatives has been established, utilizing easily preparable (E)-2-ylidene-3-cyclohexenones and stabilized sulfur ylides.
B(C6F5)3 catalyzed cyclopropanation of 3-alkenyl-oxindoles with diazomethanes to form 25 spirocyclopropane-oxindole derivatives in good to excellent yields (up to 99%) and high diastereoselectivities (up to 20 : 1 d.r.) under mild reaction conditions.
This review outlines recent advances in synthesizing gem-C,C-glycosides (i.e., glycomimetics with quaternary pseudo-anomeric centers), emphasizing innovative approaches like C–H activation and HAT methods.