Acroleins monodentate

Monodentate dipolarophiles such as acrolein, methacrolein, and a-bromoacrolein could be successfully utilized in the l ,J -DBFOX/Ph-transition metal complex-catalyzed asymmetric nitrone cycloadditions [76]. The reactions of N-benzylideneani-line N-oxide with acrolein in the presence of the nickel(II) aqua complex R,R-DBF0X/Ph-Ni(C104)2 3H20 (10mol%) and MS 4 A produced a mixture of two regioisomers (5-formyl/4-formyl regioisomers ca 3 1). However, enantio-... 

MacMillan s imidazolidinone salts, used successfully in the organocatalysed Diels-Alder reaction (see Section 8.1) also function as effective catalysts in the asymmetric nitrone cycloaddition with simple monodentate dipolarophiles. Thus acrolein (8.63) and crotonaldehyde (8.99) both react with acyclic C-aryl, N-benzyl nitrones and C-aryl N-alkyl nitrones such as (8.198) with high ees ranging from 90 to 99% in the presence of the perchlorate salt of imidazolidinone (8.91). 

For the diazoacetates, Mamoka and coworkers reported on the chiral titanium BINOLate-catalyzed highly enantioselective 1,3-dipolar cycloaddition reactions between diazoacetates and monodentate a-substituted acroleins, which give 2-pyrazolines with an asymmetric tetrasubstituted carbon center in 2006 (Table 7.6) [23], The titanium BINOLates, such as (5)-BlNOL/Ti(OPr )4 (2 1 molar ratio) complex (TB-b) and bis (5)-binaphthoxy)(isopropoxy)titanium oxide (TB-c), showed good results in terms of yields and enantiose-lectivities compared with simple (5)-BINOL/Ti(OPr )4 (1 1 molar ratio) complex (TB-a). The synthetic utility of the present reaction was further demonstrated by the total synthesis of a bromopyrrole alkaloid manzacidin A (Scheme 7.13), which was isolated firom the Okinawan sponge Hymeniacidon sp. [24],... 

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