Michael-induced ring closure reaction

Cyclopropanation reaction via Michael-induced ring closure reaction... 

CYCLOPROPANATION REACTION VIA MICHAEL-INDUCED RING CLOSURE REACTION... 

Michael additions followed by further Michael additions have become popular reactions and are usually referred to as Michael Michael Induced Ring Closure (MIM1RC) reactions. A three component Michael-Michael-aldol reaction of ketone enolates with acrylates can be achieved, resulting in the formation of six-membered ring compounds with good efficiency and high diastereoselectivites319. 

A large number of MIRC ( Michael addition induced ring closure ) reactions lead from a,j8-unsaturated carbonyl or nitrile substrates to cyclopropylcarbonyl products. These reactions do not have allylic intermediates and are treated in Section 1.1.2. 

Alkyl-3-(styrylsulfonyl)thioureas, obtained in the form of their potassium salt by reaction of styrylsulfonamides with alkyl isothiocyanates and potassium carbonate in refluxing acetone, cyclize in weakly alkaline solution, or thermally upon melting (usually at 130 160 °C) via a Michael-induced ring closure to give AT-alkyl-5-aryl-5,6-dihydro-1,4,2-dithiazin-3-amine 1,1-dioxides l.9,16,I9,31,32... 

The asymmetric synthesis of cyclopropanes has attracted continual efforts in organic synthesis, due to their relevance in natural products and biologically active compounds. The prevalent methods employed include halomethylmetal mediated processes in the presence of chiral auxiliaries/catalysts (Simmons-Smith-type reactions), transition-metal-catalyzed decomposition of diazoalkanes, Michael-induced ring closures, or asymmetric metalations [8-10,46], However, the asymmetric preparation of unfunctionahzed cyclopropanes remains relatively undisclosed. The enantioselective activation of unactivated C-H bonds via transition-metal catalysis is an area of active research in organic chemistry [47-49]. Recently, a few groups investigated the enantioselective synthesis of cyclopropanes by direct functionalization reactions. 

One of the most important classes of Michael initiated ring closure processes in the construction of carbo- and heterocycles are stepwise cycloaddition reactions where a metal induces dipolar behavior in otherwise unreactive organic compounds to be reacted with activated olefins. In this area, Pd-assisted cycloaddition reactions which involve zwitterionic zr-allylPd complexes of type I (linear type), II, or III (Pd-Trimethylenemethane (TMM) type and analogs) as reactive dipole partners are popular methods that provide highly functionalized, saturated ring systems often with high stereocontrol and atom economy (Scheme 1). Discovered in the early 1980s, they have been extensively covered in the review literature [8-16]. 

Rearrangements of complex aziridines can also result in interesting cyclic structures. For example, Zwanenburg and co-workers <1996T12253> have applied the Michael reaction-induced ring-closure (MIRC) reaction to aziridinyl... 

Under catalysis by tris(dimethylaminosulfonium)difluorotrimethylsilicate, 1,5-anhydro-4,6-0-benzylidene-2-deoxy-D-ery//iro-hex-3-ulo-l-enitol reacted with the ketene acetal, l-methoxy-2-methyl-l-(trimethylsilyloxy)-propene, by Michael reaction at C-1 and gave 23. When the catalyst involved was trimethylsilyl triflate the branched derivatives 24 and 25 unexpectedly resulted. These latter products were thought to arise by a trimethylsilyl triflate induced non-selective cleavage of the benzylidene acetal of the initially formed intermediate 23 affording 4-0- and 6-0-benzylic carbenium ions which underwent a subsequent ring closure at C-2. (See Chapter 13 for reaction of the same ketene acetal with glycals). ... 

Closure of the nonaromatid ring of the anthracycline system has been effected by condensation of a 2-(3-oxobutyl)anthraquinone with nitromethane [135]. After the initial Henry reaction, a Michael-type reaction is induced by the quinone carbonyl in spite of the high electron density of the aromatic ring to be attacked, and the site of attack being a donor. 

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