Unconventional Transformations of Morita–Baylis–Hillman Adducts

Abstract

Morita–Baylis–Hillman (MBH) adducts are versatile starting materials widely employed in Lewis base catalysis. A myriad of different transformations have been reported based on either allylic alkylations with stabilised nucleophiles or annulations with diverse dipolarophiles. Apart from these two conventional types of reactivity, MBH adducts have recently been implemented in alternative and complementary catalytic strategies, including: (i) one-pot and cascade transformations, where additional chemical bonds are formed following the asymmetric allylic alkylation event in a single synthetic operation; (ii) regioselective α-allylations for the synthesis of trisubstituted alkenes; and (iii) dual activation strategies, involving Lewis base catalysis together with transition metal complexes or light, enabling allylic alkylations with nonstabilised nucleophiles and cascade processes. The present Short Review summarises the most significant unconventional catalytic transformations of racemic MBH adducts reported within the last decade.1 Introduction2 Multi-Step Single-Vessel Transformations (path iii)2.1 One-Pot Transformations2.2 Cascade Transformations3 α-Allylations (path iv)3.1 SN2′ Mechanism3.2 SN2′–SN2 Mechanism3.3 Miscellaneous Mechanisms4 Dual Activation (path v)4.1 MBH Adduct as Electrophile4.2 MBH Adduct as Nucleophile5 Summary and Outlook

Catalyst-Free α-Allylation of Dihydroisoquinolines with Morita–Baylis–Hillman Carbonates and Its Applications in the Construction of Benzo[a]quinolizidines

“…In the past decades, the Morita–Baylis–Hillman (MBH) carbonates have also been widely utilized as allylation agents for allylic alkylation reactions . Typically, these reactions were promoted by nucleophilic catalysts such as tertiary amines or phosphines.…”

Dearomative [4 + 2] cycloaddition of 3‐nitroindoles with ortho‐amino Morita−Baylis−Hillman carbonates to forge indole‐fused quinolines

“…On the other hand, Morita−Baylis−Hillman (MBH) carbonates are versatile synthons [28–30], including C1 , C2 , C3 , C4 , C5 , and C6 synthons, to display enormous synthetic potential in constructing various cyclic compounds via [2 + 1] [31, 32], [4 + 1] [33], [3 + n] (n = 2, 3, 4, 6) [34–38], [4 + 2] [39–42], [5 + 4] [43], and [6 + 2] [44] annulations. In particular, the o‐ acylamino‐aryl MBH carbonates that added a nucleophilic site provided more challenges and opportunities for organic synthesis that could engage [4 + 2] annulations or [6 + 2] annulations or classic [3 + 2] annulations [42].…”

Divergent Synthesis of Highly Substituted Tetrahydroquinolines and Cyclopentenes via Lewis Base Catalyzed Switchable [4 + 2] and [3 + 2] Annulations of MBH-Carbonates with Activated Olefins

“…Morita–Baylis–Hillman (MBH) adducts extensively worked as versatile substrates in numerous synthetic reactions . Especially, MBH carbonates were prone to facilely realize diverse annulation reactions, alkylations and domino reactions in the present of organic phosphines or amines catalysts, for the construction of many functionalized and biologically interesting compounds . In previous reported work, Kim and co-workers synthesized quinolines from the MBH adducts of o -halobenzaldehyde N -tosylimines through the nucleophilic aromatic substitution reaction (Scheme a) .…”