Yian Shi

Organocatalytic Oxidation. Asymmetric Epoxidation of Olefins Catalyzed by Chiral Ketones and Iminium Salts

2.6.4. Other Carbohydrate-Based Catalysts 3976 2.7. Carbocyclic Ketones 3977 2.8. Ketones with an Attached Chiral Moiety 3979 3. Chiral Iminium Salt-Catalyzed Epoxidation 3979 3.

Catalytic Asymmetric Allylic and Homoallylic Diamination of Terminal Olefins via Formal C−H Activation

This paper describes a catalytic asymmetric diamination process for terminal olefins at allylic and homoallylic carbons via formal C-H activation using di-tert-butyldiaziridinone as nitrogen source with a catalyst generated from Pd2(dba)3 and chiral phosphorus amidite ligand. A wide variety of readily available terminal olefins can be effectively diaminated in good yields with high regio-, diastereo-, and enantioselectivities.

Enantioselective Bromocyclization of Olefins Catalyzed by Chiral Phosphoric Acid

A chiral phosphoric acid catalyzed enantioselective bromocyclization of olefins is described. Various cis-, trans-, or trisubstituted γ-hydroxy-alkenes and γ-amino-alkenes can cyclize under the reaction conditions to give optically active 2-substituted tetrahydrofurans and tetrahydropyrroles in up to 91% ee.

Exploring new reactive species for cyclopropanation

Abstract An organozinc species RXZnCH 2 I generated by reacting Zn(CH 2 I) 2 with RXH was found to be an efficient reagent for the cyclopropanation of olefins at room temperature. A 50.7% ee was obtained for the cyclopropanation of trans -β-methylstyrene when a chiral alcohol was used.

Highly enantioselective epoxidation of enol silyl ethers and esters

Abstract High enantioselectivities have been obtained for asymmetric epoxidation of enol silyl ethers and asters using a fructose-derived chiral ketone as catalyst and Oxone as oxidant.

Synthetic and mechanistic studies on Pd(0)-catalyzed diamination of conjugated dienes.

Various dienes and a triene can be regioselectively diaminated at the internal double bond with good yields and high diastereoselectivity using di-tert-butyldiaziridinone (5) as the nitrogen source and Pd(PPh(3))(4) (1-10 mol %) as the catalyst. Kinetic studies with (1)H NMR spectroscopy show that the diamination is first-order in total Pd catalyst and inverse first-order in PPh(3). For reactive dienes, such as 1-methoxybutadiene (6g) and alkyl 1,3-butadienes (6a, 6j), the diamination is first-order in di-tert-butyldiaziridinone (5) and zero-order in the olefin. For olefins with relatively low reactivity, such as (E)-1-phenylbutadiene (6b) and (3E,5E)-1,3,5-decatriene (6i), similar diamination rates were observed when 3.5 equiv of olefins were used. Pd(PPh(3))(2) is likely to be the active species for the insertion of Pd(0) into the N-N bond of di-tert-butyldiaziridinone (5) to form a four-membered Pd(II) complex (A), which can be detected by NMR spectroscopy. The olefin complex (B), formed from intermediate A via ligand exchange between the olefin substrate and the PPh(3), undergoes migratory insertion and reductive elimination to give the diamination product and regenerate the Pd(0) catalyst.

Cu(I)-Catalyzed Regioselective Diamination of Conjugated Dienes via Dual Mechanistic Pathways

This paper describes the Cu(I)-catalyzed regioselective diamination of conjugated dienes using di-tert-butyldiaziridinone as nitrogen source. The internal diamination and terminal diamination likely proceed via two mechanistic pathways. Various dienes can be efficiently diaminated at the internal double bonds with high regio- and diasteroselectivity in good yield using inexpensive CuBr as catalyst.

Catalytic Diamination of Olefins via N–N Bond Activation

Conspectus Vicinal diamines are important structural motifs present in various biologically and chemically significant molecules. Direct diamination of olefins provides an effective approach to this class of compounds. Unlike well-established oxidation processes such as epoxidation, dihydroxylation, and aminohydroxylation, direct diamination of olefins had remained a long-standing challenge and had been less well developed. In this Account, we summarize our recent studies on Pd(0)- and Cu(I)-catalyzed diaminations of olefins using di-tert-butyldiaziridinone and its related analogues as nitrogen sources via N–N bond activation. A wide variety of imidazolidinones, cyclic sulfamides, indolines, imidazolinones, and cyclic guanidines can be obtained from conjugated dienes and terminal olefins. For conjugated dienes, the diamination proceeds regioselectively at the internal double bond with the Pd(0) catalyst. Mechanistic studies show that the diamination likely involves a four-membered Pd(II) species resulting from the insertion of Pd(0) into the N–N bond of di-tert-butyldiaziridinone. Interestingly, the Cu(I)-catalyzed process occurs regioselectively at either the terminal or internal double bond depending on the reaction conditions via two mechanistically distinct pathways. The Cu(I) catalyst cleaves the N–N bond of di-tert-butyldiaziridinone to form a Cu(II) nitrogen radical and a four-membered Cu(III) species, which are likely in rapid equilibrium. The Cu(II) nitrogen radical and the four-membered Cu(III) species lead to the terminal and internal diamination, respectively. Terminal olefins are effectively C–H diaminated at the allylic and homoallylic carbons with Pd(0) as catalyst and di-tert-butyldiaziridinone as nitrogen source, likely involving a diene intermediate generated in situ from the terminal olefin via formation of a π-allyl Pd complex and subsequent β-hydride elimination. When di-tert-butylthiadiaziridine 1,1-dioxide is used as nitrogen source, cyclic sulfamides are installed at the terminal carbons via a dehydrogenative diamination process. When α-methylstyrenes (lacking homoallylic hydrogens) react with Pd(0) and di-tert-butyldiaziridinone, spirocyclic indolines are formed with generation of four C–N bonds and one spiro quaternary carbon via allylic and aromatic C–H amination. With Cu(I) catalysts, various terminal olefins can be effectively diaminated at the double bonds using di-tert-butyldiaziridinone, di-tert-butylthiadiaziridine 1,1-dioxide, and 1,2-di-tert-butyl-3-(cyanimino)-diaziridine as nitrogen sources, giving a variety of imidazolidinones, cyclic sulfamides, and cyclic guanidines in good yields, respectively. In the case of monosubstituted olefins using di-tert-butyldiaziridinone as nitrogen source, the resulting diamination products (imidazolidinones) are readily dehydrogenated under the reaction conditions, leading to the corresponding imidazolinones in good yields. Esters can also be diaminated to form the corresponding hydantoins with di-tert-butyldiaziridinone in the presence of a Cu(I) catalyst. A radical mechanism is likely to be operating in these Cu(I)-catalyzed reaction processes. Asymmetric processes have also been developed for the Pd(0)- and Cu(I)-catalyzed diamination reactions. Biologically active compounds such as (+)-CP-99,994 and Sch 425078 have been synthesized via the diamination processes. The diamination reactions described herein provide efficient methods to access a wide variety of vicinal diamines from readily available olefins and show great potential for synthetic applications.

A Palladium‐Catalyzed Dehydrogenative Diamination of Terminal Olefins

Metal-mediated and catalyzed diamination of olefins provides an effective approach to vicinal diamines which are very important functional moieties contained in various biologically active compounds and are widely used as chiral control elements in asymmetric synthesis.[1-6] Recently we reported various dienes and trienes can be regio- and stereoselectively diaminated using di-t-butyldiaziridinone (2)[7] as nitrogen source and Pd(0)[8] or Cu(I)[9] as catalyst. When readily available terminal olefins were reacted with di-t-butyldiaziridinone (2) and Pd(PPh3)4, the diamination occurred regio- and diastereoselectively at allylic and homoallylic carbons to form 3, likely via an in situ formed diene (Scheme 1).[10] However, when N,N-di-t-butylthiadiaziridine 1,1-dioxide (4)[11,12] is used as nitrogen source with Pd catalyst, terminal olefins are regioselectively diaminated at terminal carbons to form 5 via a different reaction mechanism (Scheme 2). Herein, we wish to report our preliminary results on this subject. Scheme 1 Scheme 2 When terminal olefins such as 1-nonene were treated with 5 mol% Pd(PPh3)4 and N,N-di-t-butylthiadiaziridine 1,1-dioxide (4), no allylic and homoallylic diamination products similar to 3 were detected. Instead terminal diamination product 5 was formed in 34% conversion. The diamination process was further improved using 10 mol % Pd catalyst prepared from Pd2(dba)3 and tri-2-furylphosphine at higher reaction temperature. For example, treating 1-nonene (1a) with Pd2(dba)3 (0.05 equiv), tri-2-furylphosphine (0.3 equiv), and 4 (2.0 equiv) at 75 °C for 10 h gave terminal diamination product 5a in 68% yield (Table 1, entry 1). The diamination can be extended to a variety of terminal olefins (Table 1, entries 1-11) (the X-ray structure of 5f is shown in Figure 1). In all these cases, diamination products 5 were formed as major products along with small amounts of unidentified isomers. One possible isomer could result from the double bond migration of 5. In some cases (Table 1, entry 4), substantial amount of this type of isomer was observed. Figure 1 The X-ray structure of compound 5f Table 1 Catalytic Dehydrogenative Diamination[a] When a mixture of 1,3-pentadiene (6) and 1-nonene (1a) was subjected to the diamination conditions (Scheme 3), compounds 7 and 5a were formed, respectively. Diene 6 was diaminated predominately at the internal double bond [13] while terminal olefin 1a was diaminated at the terminal carbons. These results indicate that this diamination is unlikely to proceed via an in situ generated diene as in the case when di-t-butyldiaziridinone (2) was used as nitrogen source (Scheme 1). Scheme 3 While a precise reaction mechanism awaits further study, a plausible catalytic cycle is shown in Scheme 4. Pd(0) first inserts into the N-N bond of 4 to form a four-membered Pd(II) species 8, which forms complex 9 with olefin 1. Removal of an allylic hydrogen of 9 forms π-allyl Pd complex 10,[14,15] which gives allyl sulfamide 11 and regenerates the Pd(0) catalyst after reductive elimination.[16] Subsequently, 11 complexes with 8 to form 12, which then undergoes a Pd(II)-catalyzed cyclization to form 13.[17] Finally, 13 undergoes a β-hydride elimination and reductive elimination to form product 5 and sulfamide 14 with regeneration of Pd(0) catalyst. In the case of 4-phenyl substituted 1-butenes (Table 1, entries 5 and 6), some amounts of dienes were formed from β-hydride elimination of π-allyl Pd complex 10,[18,19] which is consistent with the proposed mechanism. To further probe the allylic amination process, deuterium-labled α-methyl styrenes 15 and 16 were subjected to the reaction conditions. Although these two substrates were found to be less reactive due to steric effect, some amounts of allylic amination products were isolated, and the deuterium was almost equally distributed at terminal and allylic positions of the olefin in both cases (Scheme 5), which suggests that the initial allylic amination from π-allyl Pd complex 10 is a viable process (Scheme 4). Scheme 4 A proposed catalytic cycle for diamination Scheme 5 Clear identification and isolation of allyl sulfamide 11 from the crude reaction mixtures generally proved to be difficult. However, in the case of Table 1, entry 1, trace amounts of the allyl sulfamide in the reaction mixture could be detected by 1H NMR and GC-MS. Thus allyl sulfamides 19 and 20 were prepared and subjected to the reaction conditions (Scheme 6). These sulfamides indeed cyclized to form compound 5a in good yield. However, no cyclization was observed without di-t-butylthiadiaziridine 1,1-dioxide (4) (Scheme 6). These results are in agreement with the mechanism described in Scheme 4. The exact mechanism for the Pd(II)-catalyzed cyclization of 11 to form 5 awaits further study. Scheme 6 In summary, a variety of terminal olefins have been dehydrogenatively diaminated at terminal carbons using N,N-di-t-butylthiadiaziridine 1,1-dioxide (4) as nitrogen source and Pd as catalyst, giving the diamination products in high regioselectivity. The diamination is likely to proceed via Pd-catalyzed allylic amination and subsequent cyclization. This diamination is mechanistically distinct from the previous process using di-t-butyldiaziridinone (2) as nitrogen source, thus resulting in different regioselectivity. Further efforts will be devoted to studies of the reaction mechanism, search for a more effective catalytic process, and expansion of the substrate scope as well as development of an asymmetric process.

Enantioselective Bromoaminocyclization of Allyl N-Tosylcarbamates Catalyzed by a Chiral Phosphine–Sc(OTf)3 Complex

An effective enantioselective bromoaminocyclization of allyl N-tosylcarbamates catalyzed by a chiral phosphine-Sc(OTf)3 complex is described. A wide variety of optically active oxazolidinone derivatives containing various functional groups can be obtained with high enantioselectivities.