Michael Initiated Ring Closure

More recently, Tardella and co-workers reported that treatment of 2-trifluorome-thyl acrylate 36 (Scheme 3.12) with the anion generated from nosyloxycarbamate 37 gave rise to aziridine-2-carboxylate 38 in 96% yield and 72% de with undetermined stereochemistry [40]. Aza-MIRC (Michael-initiated ring closure) was used to account for this transformation. A number of other hydroxylamine derivatives have been employed successfully in this type of aziridination reaction, includ-... 

An indirect nucleophilic opening is depicted in Scheme 24. The functionalized vinyl aziridine 37 undergoes a Michael-initiated ring closure (MIRC) reaction upon treatment with suitable nucleophiles to give cyclopropanes with concomitant opening of the aziridine ring [34]. 

In addition, we were able to extend the tandem hetero Michael addition/a-ester-enolate alkylation protocol by an intramolecular variant via a Michael-initiated ring closure (MIRC) reaction leading to diastereo- and enantiomerically pure trans-configured 2-amino-cycloalkanoic acids 30 (Scheme 1.1.7) [14c,d]. 

Amputch, M. A. Matamoros, R. Little, R. D. Asymmetric induction in the Michael initiated ring closure reaction. Tetrahedron 1994, 50, 5591-5614. 

A sugar-derived vinyl sulfone (92) was found to undergo a Michael-initiated ring closure (MIRC) process to build up a chiral polysubstituted oxolan system with high stereoselectivity, yielding the all-syn stereoisomer (93) (Scheme 25).61 The observed MIRC selectivity demonstrates that the 5-exo-trig process is strongly... 

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]. 

D. Michael-initiated Ring Closure Reactions with Ketone Enolates.. 384... 

An interesting feature of Michael addition reactions is that Michael acceptors with a leaving group (mostly halides) in y-position can be used for the synthesis of cyclopropanes. The so-called Michael-initiated ring closure reaction (MIRC reaction) starts with an addition of a nucleophile to the a,/3-unsaturated carbonyl, and afterwards the intermediate enolate displaces the leaving group to give the desired cyclopropanes. ... 

The utility of the SAMP/RAMP hydrazone method in diastereo- and enantioselective Michael additions was demonstrated in the synthesis of 5-oxo esters " (eq 9), -lactones (eq 10), 0x0 diesters and dinitriles, heterocyclic compounds (eq 11), MIRC (Michael initiated ring closure) reactions, and 2-substituted 4-oxo sulfones. ... 

In 2004, Fioravanti, Pellacani, and Tardella reported the asymmetric aza-Michael-initiated ring closure additions of ethyl nosyloxycarbamate to 2-(phenylsulfanyl)-2-cycloalkenones using the cinchona-based PTCs 11 or 29, affording the corresponding aziridines with moderate ee values (Scheme 5.25) [31]. Interestingly, this reaction afforded the same enantiomer, regardless of which pseudoenantiomer of the cinchona-derived catalyst was employed. However, the absolute configuration of the products was not determined in this study. 

A convenient procedure for the preparation of geminally disubstituted cyclopropanes is the successive alkylation and cyclization of active methylene compounds with 1,2-dihaloal-kanes. - This reaction can be termed a substitution initiated ring-closure reaction (SIRC), in analogy with the Michael initiated ring-closure reaction discussed in Section 1.1.3.7. 

In recent decades, a number of antitumor lignans have been synthesized, and their structure-activity correlations have been reported. Ring-A-opened podophyllotoxin lignans were synthesized by Michael Initiated Ring Closure (MIRC). Compound 67 showed the strongest inhibition of DNA topoisomerase II like 65 [55]. Naturally... 

Ring closure to three, five, six and seven membered rings by Michael Initiated Ring Closure (MIRC) especially of sulfones, stereoselective for (3+2) cycloadditions. 

Trans-ACPC with (15,25) configuration was prepared in an elegantly short pathway (Scheme 13) by Enders et al. By addition of the chiral ammonia equivalent lithiated (5)-(-)-2-methoxymethyl-1 -trimethylsilylaminopyrro-lidine (TMS-SAMP) to co-halide-substituted enoate 84, followed by Michael-initiated ring closure (MIRC), 85 was formed with 96-98% diastereoselectivity (Scheme 13). After desilylation,... 

Michael-initiated ring closures (MIRC) offer an alternative strategy towards access of cyclopropane moieties. Compared to sulfur ylide-based approaches, MIRC affords greater flexibility as readily available all l halides can be used in conjunction with a,p-unsaturated aldehydes. However, such asymmetric ot-alkylation methods have suffered from undesirable side reactions and overalkylation. In 2007, the Wang group designed an MIRC... 

Michael-type Additions and MIRC (Michael Initiated Ring Closure) Strategy... 

Scheme 7.9 Asymmetric Michael initiated ring closure reactions of a-bromo mal-onates and electron-poor alkenes to functionalised cyclopropanes catalysed by diaryl prolinols.

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