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This paper describes a diamination process using di-tert-butyldiaziridinone as nitrogen source and CuCl as catalyst. A wide variety of disubstituted terminal olefins can be efficiently diaminated in good yields under mild condition. This diamination process was used to synthesize potent NK1 antagonist Sch 425078.
Diamination of olefins provides an effective approach to vicinal diamines, which are biologically and chemically important functional moieties.1 Various metal-mediated2,3 and metal-catalyzed4-6 diaminations have been developed. Recently, we have reported the Pd(0)- and Cu(I)-catalyzed regioselective diamination of conjugated dienes and trienes7,8,9 as well as the dehydrogenative diamination of terminal olefins10,11 using di-tert-butyldiaziridinone,13,14 diaziridinimine,15 or di-tert-butylthiadiaziridine 1,1-dioxide16 as the nitrogen sources. The Cu(I)-catalyzed diamination process has also been extended to activated mono-substituted terminal olefins such as styrenes, enynes, enol ether etc.9,12 Considering the fact that 4,4-disubstituted-2-imidazolidinones (Figure 1) have been shown to be potent NK1 antagonists,17 and in conjunction with our efforts to expand the diamination scope, we have investigated the diamination of disubstituted simple terminal olefins using di-tert-butyldiaziridinone (2) as the nitrogen source (Scheme 1).8 Herein, we wish to report our studies on this subject.
Initial studies were carried out using 2-phenylpropene as the substrate and di-tert-butyldiaziridinone (2) as the nitrogen source. When Pd(PPh3)4 was used as catalyst, only a trace amount of diamination product was observed. However, >95% conversion was obtained when the reaction was carried out with 5 mol % of CuCl-PPh3 (1:1) in CDCl3 at 65 °C.18 As shown in Table 1, various 2-phenylpropenes with different substituents on the phenyl ring can be successfully diaminated in moderate to good yield (Table 1, entries 1-9).19 2-Isopropenylnaphthalene 1j is also an effective substrate (Table 1, entry 10). Substrates with different alkyl substituents (such as ethyl, benzyl, and methoxymethyl groups) can also be diaminated in 55-71% yield (Table 1, entries 11, 12, 13, and 14). The diamination process can also be extended to α,β-unsaturated esters (Table 1, entries 15 and 16). However, dialkyl terminal olefins, such as 2-methyl-3-phenyl-1-propene, are not effective substrates for this diamination.
The deprotection of the diamination products was investigated with compound 3a (Scheme 2). Treating 3a with CH3SO3H in hexane (1:10, v/v) at room temperature gave monodeprotected compound 4a in 99% yield.20 The structure of compound 4a was confirmed by NOE analysis and X-ray structure of related compound 14 (Figure 2, Scheme 4). When the deprotection was carried out at 65 °C, both tert-butyl groups were smoothly removed in 85% yield. Free diamine 6a can be obtained in 87% yield directly from 3a by deprotection with concentrated HCl.7c,10
The application of this catalytic diamination to the synthesis of potent NK1 antagonist 4,4-disubstituted 2-imidazolidinone Sch 42507817 is outlined in Scheme 3. Disubstituted terminal olefin 9 was readily prepared in 77% yield by reaction between α-bromomethylstyrene (7) and commercially available (R)-1-(3,5-bis(trifluoromethyl)phenyl)ethanol using NaH as base. Diamination of olefin 9 with CuCl-P(OPh)3 and di-tert-butyldiaziridinone (2) gave 4,4-disubstituted 2-imidazolidinones 10 and 11 in 35% and 30% yield respectively,21 after flash chromatography (the less polar spot on the TLC corresponds to compound 10). Removal of both tert-butyl groups of compound 10 provided compound 12 (Sch 425078) in 74% yield.
To further confirm the configuration of the diamination product 10, one tert-butyl group was selectively removed using CF3CO2H at room temperature to give compound 13, which was converted to compound 14 with n-BuLi and benzoyl chloride22 (Scheme 4). The structure of compound 14 was determined by X-ray analysis (Figure 2). The determination of the structure of monodeprotected product 13 supports the structure assignment of mono-deprotected compound 4a in Scheme 2.
In summary, a variety of disubstituted terminal olefins have been effectively diaminated using CuCl as catalyst and di-tert-butyldiaziridinone as nitrogen source, which provides a rapid access to various 4,4-disubstituted-2-imidazolidinones.23 In addition, the synthesis of 4,4-disubstituted-2-imidazolidinone Sch 425078 (potent NK1 antagonist) has been achieved in three steps using this diamination. The ability to selectively remove one or two protecting groups would provide opportunities to introduce different substituents on the nitrogens if desired. Future efforts will be devoted to the development of an asymmetric diamination process and its applications.
We are grateful to the generous financial support from the General Medical Sciences of the National Institutes of Health (GM083944-02).
Supporting Information Available: The experimental procedures, the characterization of diamination products 3, NOE studies of compund 4a, and the 1H and 13C NMR spectra of compounds 3, 4a, 5a, 6a, and 9-14 along with the X-ray data of compound 14 (74 pages). This material is available free of charge via the Internet at http://pubs.acs.org.