Oxiranes vinylic, cycloaddition

The palladium-catalyzed [3 + 2] cycloaddition of vinylic oxirane 20a [42] and aziridine 20b [39] with the activated olefin 4a for the formation of five membered cyclic ether 21a and pyrrolidine derivative 21b has also been reported in our laboratories. The mechanistic issue is very much similar to that discussed in Scheme 9. Pd(0) catalyst added oxidatively to 20 to produce the 7r-allylpalladium complex 22. The Michael addition of a hetero nucleophile in 22 to the activated olefin 4a gives 23 which undergoes intramolecular nucleophilic attack on the inner 7r-allylic carbon atom to give the cy-clized products 21 and Pd(0) species is generated (Scheme 10). Similarly, the palladium-catalyzed [3 + 2] cycloaddition of vinylic oxirane 20a with the N-losylimincs 24 is also known (Scheme 11) [43]. Intermolecular cycloaddition of vinyl epoxides and aziridines with the heterocumulenes such as isocyanates, carbodiimides and isothiocyanates is also known [44,45]. Alper et al. reported the regio- and enatioselective formation of the thiaolidine, oxathiolane, and dithiolane derivatives by the palladium-catalyzed cyclization reaction of 2-vinylthiirane with heterocumulenes [46]. 

Synthesis of 1,3-oxazolidines 285 has been described by a palladium-catalyzed cycloaddition of vinylic oxiranes 284 with Af-tosyl imines 283 (Scheme 81) <2000H(52)885>. This reaction proceeded with high yields and good regioisomeric selectivity and the palladium catalyst of choice was a 1 2 Pd(dba)2 DPPE complex. 

Along similar lines, Pd(0)-catalyzed cycloadditions of isocyanates to vinyl oxiranes invariably give rise to m-oxazolidin-2-ones, irrespective of the stereochemistry of the starting oxirane <87JA3792, 89TL3893), see also <88TL99>. 

We reported that the palladium-catalyzed [3 + 2]-cycloaddition of vinylic oxirane and aziridine 631... 

A diastereoselective tandem intramolecular hetero-5 + 2-cycloaddition/Claisen rearrangement of vinylic oxirane-alkyne substrates using a rhodium NHC complex to provide regiospecific and diastereoselective access to [3.1.0] bicyclic products has been reported (Scheme 153). ... 

The palladium-catalysed regioselective 3 + 2-cycloaddition of vinylic oxiranes with imines produces the corresponding 1,3-oxazolidines in good to excellent yields. The thermal hetero 1,3-dipolar cycloaddition of trimethylenemethane with IV-sulfonyl- and A-acyl-imines produce o -methylene-y-pyrrolidone acetals which can be hydrolysed to y-amino acids. ... 

The Rh-catalyzed intramolecular cycloaddition has proven reliable for the construction of polycyclic carbocycles and heterocycles. The cascade processes involving this reaction have also been achieved. A recent example is the cascade intramolecular hetero-[5 + 2] cycloaddition/Claisen rearrangement reaction of vinylic oxirane-aUcyne substrates 73, which uses the rhodium NHC complex as catalyst and provides atom-economical, regiospecific, and diastereoselective access to [3.1.0] bicyclic products 74 (Scheme 5.50) [48]. 

This type of complex also efficiently induced the intra- and intermolecu-lar [4+2] and intramolecular [5+2] cycloaddition reactions shown in Scheme 8.10. However, these eatalysts were not effective for the mtermolecular [5+2] cycloaddition reaction. The [(IPr)RhCl(COD)]/AgSbF6 system has several attractive features, such as mild reaction conditions (15-20 °C) combined with high yields (up to 99%) and high turnover numbers (up to 1900). This [(NHC)Rh]-based system also efficiently eatalysed the diastereoselective tandem hetero-[5+2] cyeloaddition/Claisen rearrangement reaction of vinylic oxiranes with all nes. A complete ehirality transfer in the tandem process was observed, thus providing a novel and efficient method to access [3.1.0] bicyclic targets in an enantioselective manner. ... 

The [5+2] cycloaddition has been included in several domino processes. For example, Feng and Zhang have recentiy developed a novel, regiospecific, and diastereoselective domino intramolecular hetero-[5+2] cycloaddition-Claisen rearrangement of vinylic oxirane-alkyne substrates 90, which employed the rhodium Af-heterocyclic carbene complex, RhCl(/-Pr)(cod), as catalyst [95]. The process provided the corresponding [3.1.0] bicyclic products 91 in moderate to high yields (47-92%), as shown in Scheme 20.39. The authors have demonstrated the complete chirality transfer by performing the reaction with an enantiomerically enriched... 

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