Enantioselective crossed intramolecular [2+2] photocycloaddition reactions mediated by a chiral chelating Lewis acid

Abstract

In intramolecular [2+2] photocycloaddition reactions, the two tethered olefins can approach each other in a straight or in a crossed fashion. Despite the fact that the latter reaction mode leads...

Synthesis of polysubstituted bicyclo[2.1.1]hexanes enabling access to new chemical space

“…22 Recently, Mykhailiuk and co-workers reported a UV light/benzophenone-mediated protocol to bridge-substituted 1,5-disubstituted BCHs that could function as ortho -substituted benzene bioisosteres (Scheme 1C). 17 b ,23,24 However, this reactivity platform is extremely versatile and we believed it could be used to give targeted access to the 10 different exit vectors of BCHs (Scheme 1D). This in turn would enable preparation of a whole range of differently-substituted BCHs, containing various combinations of bridge and bridgehead substituents, consistent with the reaction design criteria outlined above.…”

Visible Light-Induced Regio- and Enantiodifferentiating [2 + 2] Photocycloaddition of 1,4-Naphthoquinones Mediated by Oppositely Coordinating 1,3,2-Oxazaborolidine Chiral Lewis Acid

“…A more selective excitation at 550 nm (with a filtered xenon lamp, entry 2) afforded a very comparable regioisomeric ratio with a slight improvement in enantioselectivities (48 and 39% ee), although the conversion rate was considerably decreased. It is to note that the formation of crossed adduct ( 3a ) in the enantioselective fashion is exceptional, while the enantioselective crossed cycloaddition of 2-(alkenyloxy)­cyclohex-2-enones has been realized very recently using 2 mol % rhodium Lewis acid as a chiral catalyst . The solvent also plays a significant role in the enantioselectivities, while the yield and regioisomeric ratio were not much affected (entry 3 and 4).…”

Catalytic Asymmetric Visible-Light de Mayo Reaction by ZrCl4-Chiral Phosphoric Acid Complex

“…While this reaction has been widely applied in the total synthesis of natural products, , the development of a catalytic asymmetric de Mayo reaction has remained to be accomplished despite of the prevalence of visible-light strategies in asymmetric catalysis . The challenge stems from generating high-energy excited species under mild conditions and achieving stereoselective control during the excited-state cycloaddition process . Herein, we reported the first visible-light-promoted catalytic asymmetric de Mayo reaction by the use of a photoresponsive chiral Zr-CPA-enolate complex (Scheme A, right).…”