Allenyl sulfonamide

The oxidation of allenylsulfonamides 75 is also possible by using DMDO [23], Unlike the corresponding reaction of allenyl acids, oxidation of allenyl sulfonamides usually cannot be stopped after the formation of the allene oxide 76 but proceeds further to the spirodiepoxide intermediate 77, finally giving hydroxypyrrolidinone 78 and hydroxypiperidone 79, respectively (Scheme 17.23). Similarly to y-allenyl alcohols, aldehydes and acids, five-membered heterocycles, e.g. 80, are also formed from y-allenylsulfonamides. In the latter case the reaction can be terminated after the first epoxidation by addition of p-toluenesulfonic acid. 

Kang et al. [36] found that allenyl sulfonamides also undergo cyclocarbonyla-tion catalyzed by Ru3(CO)12 to give a,/J-unsaturated y-lactams (Eq. 21). 

Krause has shown that gold(III) salts catalyze the intramolecular emJo-hydroamina-tion of N-protected a-aminoallenes [35]. For example, treatment of the diasteromeri-cally pure a-allenyl sulfonamide 44 with a catalytic amount of AUCI3 in dichlor-omethane at 0 °C for 1 h formed the pyrroline derivative 45 in 95% yield with 96% diastereomeric purity (Scheme 11.6). The protocol tolerated aryl and alkyl substitution of the distal allenyl carbon atom and was also effective for the hydroamination of N-unprotected a-allenylamines although these latter transformations required considerably longer reaction time. In a similar manner, Lee has reported the gold (Ill)-catalyzed ewdo-hydroamination of 4-allenyl-2-azetidinone 46 to form bicydic P-lactams 47 (Eq. (11.25)) [36]. 

Yamamoto has reported the intramolecular e%o-hydroamination of N-allenyl sulfonamides and carbamates catalyzed by simple, unligated gold(I) and gold(III) salts. Noteworthy was that cyclization of N-allenyl sulfonamide derivatives that possessed an axially chiral allenyl moiety occurred with highly selective transfer of chirality to the newly formed tetrahedral stereogenic carbon atom [38]. For example, treatment of enantiomerically enriched y-allenyl tosylamide 52 (96% ee) with a catalytic amount of AuCl in THF at room temperature led to isolation of ( )-2-(l-heptenyl)pyrroldine ( )-53 in 99% yield with 94% ee (Eq. (11.28)). 

Toste has described the intramolecular enantioselective hydroamination of y- and 6-aUenyl sulfonamides catalyzed by enantiomerically pure bis(gold) phosphine complexes [42]. For example, treatment of the terminally-disubstituted y-allenyl sulfonamide 59 with a catalytic amount of [(R)-3,5-xylyl-binap](AuOPNB)2 (OPNB =p-nitrobenzoate) formed protected pyrrolidine 60 in 88% yield with 98% ee (Eq. (11.34)). Likewise, treatment of 6-allenyl sulfonamide 61 with a catalytic amount of [(JJ)-Cl-MeObiphep](AuOPNB)2 in nitromethane at 50 °C for 24h formed 2-alkenyl piperidine 62 in 70% isolated yield with 98% ee (Eq. (11.35)). Realization of high enantioselectivity in this protocol required employment of both a terminally disubstituted allene and a sulfonamide nucleophile. 

Toste has developed an alternative approach to the enantioselective hydroamina-tion of N-allenyl sulfonamides that employs a chiral or achiral gold complex in combination with a chiral phosphonate anion [43]. As an example of this approach, treatment ofy-allenyl sulfonamide 63 with a catalytic 1 1 mixture of the achiral mono (gold) phosphine complex (PMe2Ph)AuCl and chiral, enantiomerically pure silver phosphonate Ag-( J )-64 (5 mol%) in benzene at room temperature for 48 h formed 2-alkenyl pyrrolidine 65 in 84% isolated yield with 99% ee (Eq. (11.36)). 

Cyclohydroaminations of y-Allenyl Sulfonamides with Mono-, Bis-, and Trisphospholane Gold(l) Catalysts... 

The gold(l)-catalyzed cycloamination of y-allenyl sulfonamides as reference reaction allowed us to study the influence of the nuclearity of the catalysts on their catalytic performance. Interestingly, the C3-symmetric trinuclear complex was found to surpass its mono- and dinuclear congeners both in terms of activity and enantioselectivity (up to 95% ee) (Scheme 15.19). 

The allenylindium intermediates are prepared by treatment of the aziridines with Pd(PPh3)4 in THF-HMPA containing 1 equivalent of water. In the presence of iso-butyraldehyde the expected adducts were formed with excellent diastereoselectivity (Tables 9.56 and 9.57). Interestingly, the reaction did not proceed in the absence of water. It is suggested that water is needed to protonate the sulfonamide anion of the initially formed allenyl palladium species (Eq. 9.150). 

An a-allenic sulfonamide undergoes Pd-catalyzed carbonylative cyclization with iodobenzene, affording a mixture of isomeric heterocycles (Scheme 16.12) [17]. The coupling reaction of an allene with a PhCOPdl species takes place at the allenyl central catrbon to form a 2-acyl-Jt-allylpalladium complex, which is attacked by an internal sulfonamide group in an endo mode, affording a mixture of isomeric heterocycles (Scheme 16.13). 

In situ epoxidation of allenyl alcohols [20], aldehydes [21], acids [22] and sulfonamides [23] followed by intramolecular ring opening of the intermediates was thoroughly investigated by Crandall and co-workers. They showed that products formed either from the allene oxide or the spirodioxide intermediate can be prepared selectively. Allenyl acids 56, for example, react first with DMDO on their more substituted double bond. When the concentration of the oxidant is low (DMDO is formed... 

A new type of triaryl phosphine-functionalized imidazolium salt containing cations such as (6) has been prepared. Palladium complexes of (6) generated in situ have been used successfully in Heck-type reactions of aryl halides with acrylates and of 4-bromotoluene with styrene derivatives.34 The first Heck-type reaction of aryl halides with allenes has been reported. 1,3-Double arylations were observed with 3-substituted-l,2-allenyl sulfones, while 1-monoarylation was favoured with 3,3-disubstituted-l,2-allenyl sulfones.35 It has been shown that the a-arylation of methane-sulfonamides (7) may be achieved using palladium catalysis reaction proceeds through the sulfonamide enolates.36 It is also reported that palladium cross-coupling of alkynes with /V - (3 - i odophe n y I an i I i ncs) may lead to the formation of substituted carbazoles.37... 

The enantioselective hydroaminations of allenes with chiral phosphine catalysts was accomplished with substrates that had a terminal symmetric substitution and with the amines protected as carbamates or sulfonamides. The same symmetric substituents were necessary for the enantioselective transformation nsing chiral counterions. However, very recently, high enantiomeric excesses were reached with trisubstituted asymmetric allenes by a dynamic kinetic enantioselective hydroamination of allenyl carbamates (eqnation 110), even thongh the E/Z ratio of the prodncts was not optimal. 

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