Angelw: rhodium catalyzed cyclization of o-alkenyltrifluoromethylsulfonylaniline with alkynes to form naphthalene derivatives

At present, transition metal catalyzed C-H bond activation has been widely used to construct carbon carbon bond and carbon heterobond In addition to simple functionalization, C-H bond activation can also realize oxidation and cyclization, which provides a practical method for the construction of a variety of ring structures, especially heterocycles Recently, associate professor mois é s Gul í as and Professor Jos é L Mascare ñ as of the University of de Compostela, Santiago, Spain, reported the method of Cp * Rh (III) catalyzing the reaction of 2-alkenylphenol with alkyne to form 7-membered oxyheterocycles or spirocyclic products (scheme 1a) Recently, the team has also developed a method for the efficient synthesis of naphthalene derivatives from o-alkenyltrifluoromethylsulfonylaniline and alkynes catalyzed by Cp * Rh (III) This [4C + 2C] cyclization is the first reaction involving the cleavage of the double C-H bond of the inactive substrate Interestingly, in addition to the direct cyclized cycloaddition products, the rearranged isomerized addition products (scheme 1b) can also be obtained through the 1,2-migration of alkenyls Relevant articles were published on angelw Chem Int ed (DOI: 10.1002/anie.201811747) (source: angelw Chem Int ed.) at the beginning of the study, the author studied the reaction activity of 2-propenylamine with different substituents on nitrogen with Diphenylacetylene (2a) in the air atmosphere, using acetonitrile as solvent, [Cp * RhCl 2] 2 as catalyst, 0.5 equivalent Cu (OAC) 2 · H 2O as additive Even aniline with acetyl, trifluoroacetyl, tert butoxycarbonyl (BOC), p-toluenesulfonyl (TS) and p-nitrobenzenesulfonyl (NS) and unprotected aniline could not react It is gratifying that naphthylamide 3AA and 4AA (Table 1, entry1) can be obtained from aniline (1a) containing trifluoromethylsulfonyl (TF), although the overall yield is low Subsequently, the author found that 3AA and 4AA (entry 7) could be obtained by reaction of 1a and 2A in THF with [Cp * RhCl 2] 2 as catalyst and NaOAc as additive (source: angelw Chem Int ed.) under the optimal reaction conditions, the author first investigated the applicable range of various alkynes (Table 2) The products of naphthylamide can be obtained with excellent yield and good selectivity by electron rich or electron deficient symmetrical diaryalkynes (2b and 2C) However, the cycloaddition product of asymmetric alkylarylalkynes (2D and 2e) has a good yield and only one regional isomer In addition, aliphatic alkynes (2f and 2G) can also react smoothly to obtain cycloaddition products in medium yield (source: angelw Chem Int ed.) then, the author used 4-octyne as the coupling to investigate the application scope of o-alkenyltrifluoromethylsulfonylaniline As shown in Table 3, naphthalene amide 4BF, 4CF and 4df have good yield (66% - 90%) and excellent selectivity (> 20:1) Curiously, the unsubstituted vinylaniline 1E did not yield the target product The reaction can also be compatible with other aromatic rings with electron rich or electron deficient substituents The corresponding naphthylamide product (4FF - 4Jf) was obtained from trifluoromethylsulfonylaniline substrates with O -, M - and p-linked methyl, methoxy or trifluoromethyl groups in good yield and good regioselectivity (source: angelw Chem Int ed.) finally, through mechanism experiment and DFT calculation, the author thinks that the catalytic process starts from the C-H bond activation of alkenyl (scheme 4), and the rhodium ring I is obtained first Rhodium is turned over and activated by the second C-H bond to obtain the intermediate II ', which can eliminate the product 3 (path a) by migration insertion and reduction of alkynes However, what is the mechanism by which naphthalene 4 'is obtained? Intermediate I can also obtain intermediate III through migration and insertion of alkynes, which is eliminated by [1,3 '] - reduction to produce spiral ring IV (path B) (source: angelw Chem Int ed.) in fact, DFT calculation confirmed the feasibility of the above path B from energy, and its energy barrier is lower than that of II 'formed by C-H bond activation The calculated data also show that the rhodium (I) - spiro complex can be rapidly converted into cyclopropyl tricyclic intermediate VA or VB When r = PR, the kinetics is favorable for the formation of VB (Figure 1) The reason may be that when PR exists, the structure of transition state of VA will have larger steric hindrance VB has a lower energy barrier and tends to form rearrangement addition products, which is consistent with the experimental results Rhodium hydrogen coordinated naphthylamide VI was obtained by aromatization of intermediate V via ring expansion (source: angel Chem Int ed.) conclusion: Associate Professor mois é s Gul í as and Professor Jos é L Mascare ñ as have found a new rhodium catalyzed oxidation and cyclization involving the activation of double C-H bonds The reaction is characterized by simple operation, high atom economy, high chemical and regional selectivity and wide synthesis range Importantly, the novel mechanism of the cyclization, including the rearrangement process realized by the cleavage and formation of C-C bonds, has been revealed.