Gold-Catalyzed Atom-Economic Synthesis of Sulfone-Containing

Feb 13, 2019 - Treatment of 2a with LiAlH4 could remove the sulfonyl moiety, furnishing 3a in good yield. 2a could be conveniently converted to 3b and...
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Gold-Catalyzed Atom-Economic Synthesis of Sulfone-Containing Pyrrolo[2,1-a] Isoquinolines from Diynamides: Evidence for Consecutive Sulfonyl Migration Jibing Liu, Pushkin Chakraborty, ZHANG HENG, Liang Zhong, Zhi-xiang Wang, and Xueliang Huang ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.8b04934 • Publication Date (Web): 13 Feb 2019 Downloaded from http://pubs.acs.org on February 13, 2019

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is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

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ACS Catalysis

Gold-Catalyzed

Atom-Economic

Sulfone-Containing

Pyrrolo[2,1-a]

from

Evidence

Diynamides:

for

Synthesis

of

Isoquinolines Consecutive

Sulfonyl Migration Jibing Liu,a,c‡ Pushkin Chakraborty,a‡Heng Zhang, a,c‡ Liang Zhong,b‡ Zhi-Xiang Wang*b and Xueliang Huang* a,c a.

Key Laboratory of Coal to Ethylene Glycol and Its Related Technology, Center for Excellence

in Molecular Synthesis, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, China b. School

of Chemical Sciences, University of the Chinese Academy of Sciences, Beijing 100049,

China c.

University of Chinese Academy of Sciences, Beijing 100049, China

ABSTRACT

A gold-catalyzed cascade reaction of conjugated diynamides has been developed. In this way, a series of sulfone containing pyrrolo[2,1-a]isoquinolines featuring the core structural motifs of lamellarin alkaloids were prepared atom economically. Mechanistic studies including DFT

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calculations uncovered a consecutive 1,2-migration of sulfonyl group for the formation of pyrrole ring.

KEYWORDS Diynamide, Gold catalysis, consecutive 1,2-sulfonyl shift, polycyclic heterocycles, DFT calculations.

Introduction Over the past decade, ynamides have emerged as valuable reagents in synthetic chemistry.1 Typically, there are three functional groups attached to the nitrogen atom, including (1) an alkynyl moiety, (2) an electron withdrawing group (carbamate or sulfone) that improves the stability and controls the reactivity, and (3) R1 (normally alkyl or aryl group). The thermal stability, ambivalent nature and easy preparation2 have attracted particular interests from the synthetic chemists to develop new reactions on ynamide chemistry. In majority of these developments, the reaction modes are dictated by the formation of an “activated” keteniminium intermediate3 which can be trapped by a nucleophile. In certain intramolecular reactions, R1 serves as a nucleophilic hand to furnish a cyclic product (Scheme 1a, top). In this context, the reactions of ynamides involving alkynyl fragment and R1 moiety are well established.1 Despite these advances, the withdrawing group in ynamide mostly remains as a spectator lacking active participation. Moreover, the nitrogen atom in ynamide so far has rarely been used to construct a new C-N bond.4 Although there are a few literature reports regarding migration of groups from ynamide moiety, such a type migrations usually ended in ketenimine type products formation.5

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Hence, the utility of nitrogen atom in ynamide has been mostly restricted to activate the triple bond. To address this limitation, and on the basis of our recent developments on gold-catalyzed Scheme 1. Reaction of functionalized ynamide A. a) reaction modes of ynamides Nu

well-developed A

Nu

R 1:

EWG

N

Simple cyclic products without new C-N bond formation FG

N EWG

Nu

FG

Unknown

Easily available modular synthesis

N

EWG

FG

Polycyclic compounds with multiple bonds reorganization

valuable N-heterocycles with EWG migration Nu = proper nulceophile; EWG = electron withdrawing group; FG = functional group b) reaction design R1

R'

R' Ar [Au]

N

N

Ar

SO2R

gold assisted isomerization

N

Ar

SO2R

SO2R A

N

Ar

B

R'

SO2R

[Au] Ar

[Au] 3 2 ' R N1 SO2R

B' 1, 3-sulfonyl migration

B' "cascade reaction"

Ar [Au]

SO2R 3 2 ' R N1

C, core structure of lamellarin alkaloids

reactions,6 we conceived an intramolecular cascade cyclization of conjugated diynamide A. The overall transformation would end up in a complex polycyclic N-heterocyclic compound (Scheme 1a, bottom). To realize such a perception might be quite challenging, because not only it requires a new tethered electrophilic site, but also one of the groups attached to nitrogen atom has to be cleaved in order to restore the reactivity. Given the well-established procedure for the synthesis of ynamides, the realization of such a strategy could be of great use, as a range of complex

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polycyclic N-heterocycles could be produced in a modular fashion from easily available feedstock. To test above mentioned idea, we envisioned that a gold(I)-catalyzed reaction7 of diynamide A8 derived from 2-arylethanamine may lead to an unexplored reactivity of ynamide chemistry (Scheme 1b). The reaction was supposed to be initiated by an intramolecular arene-ynamide cyclization with a gold catalyst,9 thus furnishing a transient enynamide product B. At this stage, a gold-assisted double bond isomerization may take place, giving B́, in which the alkyne and sulfonamide have a cis relationship. Once the isomerization process reaches B́, the second active electrophilic site can be generated via coordination of gold(I) complex with the conjugated alkynyl tether. Thus the following sequence involving intramolecular amide-alkyne cyclization/1,3-sulfonyl group shift10 could eventually lead to the formation of pyrrolo[2,1a]isoquinoline C. Notably, C constitutes the core of the marine natural products lamellarin alkaloids11,12 which show a wide array of therapeutically useful biological activities.13 Results and discussion To testify our hypothesis, 3-methoxyphenyl-tethered diynamide 1a was chosen as the model substrate for the initial investigation (Table 1). To our delight, a cascade cyclization of 1a indeed occurred when IPrAuNTf2 was employed as the catalyst in DCE (1,2-dichloroethane), giving pyrrolo[2,1-a]isoquinoline 2a, a regio isomer of C in 70% yield (entry 1). Intriguingly, instead of the expected 1,3-sulfonyl migration,10c as confirmed by X-ray structure, a formal 1,4-shift of methylsulfonyl (Ms) group was observed. Control experiments highlighted the critical role of cationic nature for the gold catalyst (entry 2), and silver salt cannot catalyze current cascade reaction (entry 3). Brief examination of effects of other ligands didn’t give better results (entries

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ACS Catalysis

4 and 5). Change of counter anions (e.g. SbF6) did not improve the efficiency of the reaction. Finally, DCM (dichloromethane) was found to be a better choice compared to DCE by thorough screening of solvents as the yield was improved to 87% (entries 7-11, Table 1). Table 1. Variation of the reaction conditions for the cyclization of diynamide 1a. Ms Ph MeO

Entrya

N Ms 1a, 0.15 mmol

3

4 5 mol% IPrAuNTf2 DCE (0.15 M), 30 oC, 4 h MeO

Ph

2a

"standard conditions" variation from "standard conditions"

2 N1

yield/%

1

-

2

IPrAuCl as the catalyst

-

3

AgNTf2 as the catalyst

-

4

JohnPhosAuNTf2 as the catalyst

61

5

Ph3PAuNTf2 as the catalyst

16

6

IPrAuPhCNSbF6 as the catalyst

61

7

CHCl3 as the solvent

57

8

DCM as the solvent

87

9

PhMe as the solvent

51

10

1,4-dioxane as the solvent

51

11

MeNO2 as the solvent

37

70

a

The reaction was carried out under an atmosphere of argon. Yields reported are for pure, isolated compounds. IPr = 1,3-bis(diisopropylphenyl)imidazol-2-ylidene, JohnPhos = P(tBu)2(o-biphenyl).

With the optimal conditions in hand (entry 8, Table 1), a variety of alkoxy substituted 2phenylethan-1-amine derived diynamides 1 were prepared to examine the substrate scope of the reaction (Table 2). First, we focused on Ms protected diynamides 1a-1e with different aryl groups (R1). As seen in Table 2, a series of products 2a-2e could be obtained in excellent yields, indicating that the reaction is not affected by the substitution on phenyl group (R1). Similar to mono-methoxy substrates, the reactions of di- or tri-alkoxy group substituted diynamides produced the corresponding products 2f-2r in moderate to high yields (55%-88%). Benzyl (1n-

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Table 2. Substrate scope.a R2O2S R1

Ar N SO2R2 1

5 mol% IPrAuNTf 2 DCM (0.15 M), 30 oC, 4 h

Ms

Ms N

MeO

R3 R4

MeO

N

MeO

2b, 83%, (R3 = Me, R4 = H)

2g, 70%, (R3 = F, R4 = H)

2c, 89%, (R3 = F, R4 = H)

2h, 55%, (R3 = OMe, R4 = H) 3

2d, 72%, (R3 = Cl, R4 = H) 3

MeO

R4

2f, 85%, (R3 = H, R4 = H)

OMe 2k, 88% Ms OMe MeO

4

2i, 73%, (R = H, R = Cl)

2e, 64%, (R = H, R = Cl) Ms N

Ph

Ms

BnO

MeO

N

Ph

MeO

MeO

OMe

R R5

Ts

O

N

Ph

N MeO

O

iPrO 2p, 80%, (R5 = Ph, R = Ms)

2r, 73%

2q, 58%, (R = Me, R = Ts) Bs

Ms Ph

MeO

2s, 73% (73%b), (R3 = H)

Ms

Ms N

Ph

Ph

N

MeO

N

S

MeO

2u, 83%

2v, 55%

2w, 0%d

2x, 83%

Ms

Ms N

R5

MeO

N

R5 N

MeO

MeO

2y, 70%, (R5 = nBu) 2z, 62%, (R5 = tBu) 2aa, 80%, (R5 = cyclopropyl)

2ab, 42%c, (R5 = CH2OH) 2ac, 66%, (R5 = (CH2)2OAc)

Ph

Ph

N O 2af, 25%

Ph

OMe Ms 2ad, 65% Ms

Ms

Ms

Ms

2ae, 72%

R3

2t, 63%, (R3 = Me)

5

N

Ph

2o, 61%

Ms N

N

BnO 2n, 69%

2m, 34%

Ph

2l, 81%c

Ms

MeO

S

N

MeO

2j, 78%, (R3 = H, R4 = Me)

4

Ph

N

R3

2a, 87% (73%b), (R3 = H, R4 = H)

N

R1

2

Ms

MeO

N

Ar

N N Me 2ag, 65%

Ph

Me N

N

Ph

2ah, 45%

a The reaction was carried out in 0.15 mmol scale under an atmosphere of argon. Yields reported are for pure, isolated compounds. b Yield for gram-scale reaction. c The reaction was carried out 40 oC, 10 h. d The 1w was recovered.

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ACS Catalysis

1o) and isopropyl (1p-1q) groups did not hamper the outcomes of the reactions. Other sulfonyl groups (Ts = 4-MeC6H4SO2-, Bs = C6H5SO2-) in diynamides (1s-1u) could undergo similar migration, and the corresponding pyrrolo[2,1-a]isoquinolines 2s, 2t and 2u were isolated in 73%, 63% and 83% yields, respectively. It is noteworthy to mention that a particular conjugated triynamide 1v was also a viable substrate, providing the desired product 2v with an extended alkyne moiety unaffected, which offers a good handle for further manipulations. Furthermore, separate gram-scale reactions of 1a and 1s were carried out. The desired products 2a and 2s both were obtained in 73% yields. As anticipated, electron donating group on the phenyl ring was indeed crucial for the initial arene-ynamide cyclization, as diynamide 1w exhibited no activity under current conditions. A particular substrate 1x with thiophenyl moiety delivered the corresponding product 2x in 83% yield. Subsequently, the reactivity of diynamides comprising different aliphatic groups R1 were examined. As depicted, diynamides bearing linear (nBu-, 1y) or branched alkyl group (tBu-,1z) and cyclopropyl group (1aa) were found to be competent substrates. Remarkably, functional groups such as, free hydroxy (1ab) and acetate groups (1ac) which are prone to react with triple bonds with gold catalysis, were well tolerated as well under standard conditions (2ab and 2ac). The methodology was also found to be competent with naphthyl substrate with methoxy substituent at seventh position (1ad), furnishing the corresponding pyrrolo-azepine product 2ad in 65% isolated yield. After examining the scope of an array of substrates with aryl and naphthyl moieties, we were interested in the applicability of our strategy to heteroaromatic systems. To our delight, diynamides tethered with thiophene, furan and indole skeletons (1ae-1ah) underwent transformations in expected way, opening a new avenue for the synthesis of multipleheterocyclic systems. Unlike simple aryl substrates, the heteroaromatic rings appeared to be

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sufficiently activated, thus the presence of additional electron donating group is not compulsory to initiate the first cyclization step. Both 2 and 3-substituted indoles (1ag-1ah) ended up with corresponding regioisomeric products 2ag and 2ah. In the case of the product bearing furanyl motif, 2af was isolated in 25% yield, together with some unidentified by-products. Mechanistic Studies To understand the reaction mechanism, a crossover experiment using equally reactive diynamides 1a and 1t was carried out under standard conditions. The reaction of the mixture gave only 2a and 2t without any crossover products, indicating that the sulfonyl group migration takes place intramolecularly (Scheme 2a).14 The reaction of dihydro isoquinoline 2aá (for details, see SI) gave the tricyclic product 2a in almost quantitative isolated yield, which suggests that 2aá is an intermediate for current transformation (Scheme 2b). Scheme 2. Mechanistic experiments. Ms Ph MeO

N Ms

1a

MeO 5 mol% IPrAuNTf2 DCM (0.15 M), 30 oC, 4 h

+ pTol MeO

N Ts

1t

N

MeO

Ms

(a)

Ts

no crossover products 2b and 2s formation

N

Ph

N

2a, 84% yield +

MeO

Ph

pTol

2t, 71% yield Ms N

5 mol% IPrAuNTf2 o

DCM (0.15 M), 30 C, 4 h

Ph

(b)

MeO 2a, 94% yield

2aa'

To further gain insight into the catalytic mechanism of the reaction, in particular, the details on sulfonyl group migration, we carried out DFT study (see SI-II.1 for computational details) to

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ACS Catalysis

Ph [Au]

MeO

Ph

Ms

N

[Au]

Tf2N

H

TS1

N

3.0

1a

Ph

MeO

0.0

-5.2

IM2

Ph

IM1 -12.4

[Au] H NTf2 Ms N Ph

TS2

-6.5

[Au]+

Ms

NTf2[Au]

H

HNTf2

Ms

N

-17.1

MeO

N

Ms

TS4

Ph H

-21.6

Ms

MeO

N Ms

[Au] N

HNTf2

[Au]

[Au] C

-11.7

IM3

Ph

MeO

Ph

H

TS3

[Au]+ N Ms

NTf2-

TS5

-36.3

IM1

-43.7

-45.5

Ph

-44.4

IM5

IM4

H [Au]+ N Ms

IM6

Ph

[Au]+

H

H

[Au]+ N Ms

Ph N Ms

MeO

Tf 2N

[Au]

H

Ms

H

Ph

+ Ms N

N

TS6

-26.2

Ms H H

+

N

[Au]

Ph

N

TS10

Ph

[Au]

Ms

Ph

N+

IM6 [Au]+

TS7

-59.2

Ph

NTf 2-

-57.1

IM7

N Ms

Ph

+

N

Ph

TS8

TS9

-46.4 TS10 -52.6

-45.7

Ms

N+

H

H [Au] N

Ph IM11

Ph

N HNTf 2

-69.1

Ph

Ph TS11

Ms

TS11

[Au]

[Au]

Ms

IM10

H

NTf 2

H N

IM10

H

[Au]

Ms

[Au]

Ms

-44.4

H

Ms

[Au]

-62.2

IM8

2a

MeO

-58.6

HNTf 2

-72.8

-73.3

2a'

2a

[Au]

IM1

Ms

MeO

N+

IM1

Ph

-84.7

1a

IM11 IM9

H Ms N+

1a

-89.7

Ms

[Au] N

Ph MeO

Ph 2a'

Figure 1. Reaction pathway for the [Au]+-catalyzed transformation of 1a to 2a, along with relative free energies in kcal/mol

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Page 10 of 24

2.68

2.14

Au TS6

IPr Concerted C-N bond formation and 1,2-Ms shift

Figure 2. Optimal structure of TS6. Key bond lengths are given in angstroms. Trivial hydrogen atoms are omitted for clarity. characterize the reaction pathway leading diynamide 1a to product 2a. Figure 1 displays the most feasible pathway among the alternatives we probed (see SI-II.2). To begin with, in the presence of gold species ([Au]+ = IPrAu+), 1a undergoes intramolecular cyclization, giving IM2. The cyclization involves dearomatization, thus IM2 is 5.9 kcal/mol less stable than IM1. Afterwards, the counter anion NTf2- mediates a 1,3-H shift to rearomatize IM2, giving IM4. To further cyclize, IM4 needs to isomerize to IM6, positioning the alkynyl group cis to N-atom. The pathway from IM6 to IM8 describes the second annulation which takes place via a concerted CN bond formation and 1,2-Ms shift, as indicated by the structure of TS6 in Figure 2, followed by another 1,2-Ms shift via TS7. The connections of TS6 to IM6 backward and IM7 were confirmed by IRC (intrinsic reaction coordinate) calculations (SI-II.3). The alternative mechanisms shown in SI-II.2 are much less favorable. For examples, the transition states for suprafacial and antarafacial 1,3-Ms shifts are 24.0 and 22.6 kcal/mol higher than TS6, respectively. Subsequent to the annulation, the resultant intermediate IM8 can either undergo 1,2-H shift via TS9, affording 2a (Figure 1, in red), or a third 1,2-Ms shift via TS8, giving IM9

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ACS Catalysis

to result in the regioisomer 2a’ (Figure 1, in blue). While the barriers (c.a. 23.0 kcal/mol) are accessible, the close relative energies of TS8 and TS9 disagree with the single experimental product (2a), rather than a mixture of 2a and 2a’. However, as shown in Figure 1, the 1,2-H shift via TS8 can be greatly (c.a. by 6.0 kcal/mol) facilitated by using NTf2- as a proton transfer shuttle, thus explaining the production of the single product 2a. Energetically, as the reaction proceeds, the system becomes more and more stable, with an overall energy release of 73.3 kcal/mol. The rate-determining step lies in the isomerization of cis-IM4 to trans-IM6 with a barrier of 23.8 kcal/mol. The energetic results well explain why the reaction could take place efficiently. The concerted mechanism for C-N bond formation and Ms migration and the involvement of IM4 agree with our experimental mechanistic studies (see Scheme 2). Synthetic manipulations To exploit the synthetic utility of the products, representative experiments were conducted (Scheme 3). Treatment of 2a with LiAlH4 could remove the sulfonyl moiety, furnishing 3a in good yield. 2a could be conveniently converted to 3b and 3d, in which the Br group or OTf group provides a platform for further transition-metal-catalyzed coupling reactions (for details, see SI). Manganese dioxide enabled dehydrogenation of 2a afforded 3c smoothly. Pd-catalyzed Kumada reaction of 2s could furnish 3e. An additional feature of our protocol is the introduction of sulfonyl group onto the lamellarin core. Because of the unique biological and chemical properties, sulfone-containing molecules is of great importance.15 Accordingly, we expect that the presence of a sulfone moiety in pyrrolo[2,1-a]isoquinoline core might also possess interesting biological activity and could be a useful analogue for structure-activity-relationship (SAR) study. To further explore the

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application of our reaction, we attempted to functionalize product 2ab. Delightfully, 2ab could be converted to the corresponding methyl ester 3f with excellent yield by a Pd-catalyzed one-pot reaction (Scheme 3).16,17 According to the established protocols to prepare lamellarin derivatives,12i,12k we believe that compound 3f might be ornamented to sulfone containing lamellarin analogues. Scheme 3. Synthetic modification based on 2. Reagents and conditions: a) LAH, 1,4-dioxane, reflux, 9 h; b) NBS, THF, 0 oC to RT, 12 h; c) MnO2, DCM, reflux, 36 h; d) B(C6F5)3, Et3SiH, toluene, reflux, 7 h; e) TBAF, THF, 0 oC to RT, 2 h; f) PhMgBr, Pd(PPh3)2Cl2, THF, 80 oC, 10 h.

Ph

N MeO

3b, 95% yield

a Ph

d, e

Ms Ph

N MeO

3a, 72% yield

Ms N

Br

Ms

H

b

Ph

N MeO

3c, 59% yield Ph

c

2a

2s

N

f

Ph

MeO

HO 3d, 68% yield

3e, 42% yield (brsm 55%) MeO

Ms

2ab

Pd(PPh3)2Cl2 BnCl, K2CO3, MeOH THF, 90 oC, 16 h

MeO

N

CO2Me

3f, 85% yield

OMe

MeO O MeO

MeO

MeO

N

O

MeO

Conclusions In conclusion, we have developed a gold-catalyzed tandem reaction of 2-(hetero)-aryl-1amines derived diynamides. A remarkable feature of this transformation is the participation of all three functional moieties on the nitrogen of ynamide, thus a variety of complex sulfonecontaining pyrrolo[2,1-a]isoquinolines could be synthesized conveniently in a modular manner.

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ACS Catalysis

DFT studies have uncovered a clear picture on the migration of the sulfonyl group and wellexplained the observed regioselectivity of the products. ASSOCIATED CONTENT Supporting Information. Supporting Information (SI) available: [Experimental procedures, characterization data for new compounds (PDF), DFT calculation details, Crystal data of compounds 2a and 3f (CIF)17]. This material is available free of charge via the Internet at http://pubs.acs.org. AUTHOR INFORMATION Corresponding Author *[email protected]; [email protected]. Author Contributions ‡J. L., P. C., H. Z. and L. Z. contributed equally to this work. Notes The authors declare no competing financial interests. ACKNOWLEDGMENT We thank the financial support by NSFC (Grant No. 21502190, 21573233, 21871259), NSF of Fujian (Grant No. 2017J01031), Hundred-Talent Program and the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDB20000000). REFERENCES

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(1) For representative reviews of ynamides: (a) DeKorver, K. A.; Li, H.; Lohse, A. G.; Hayashi, R.; Lu, Z.; Zhang, Y.; Hsung, R. P. Ynamides: a Modern Functional Group for the New Millennium. Chem. Rev. 2010, 110, 5064−5106; (b) Evano, G.; Coste, A.; Jouvin, K. Ynamides: Versatile Tools in Organic Synthesis. Angew. Chem. Int. Ed. 2010, 49, 2840−2859; (c) Evano, G.; Jouvin, K.; Coste, A. General Amination Reactions for the Synthesis of Ynamides. Synthesis 2013, 45, 17−26; (d) Wang, X.-N.; Yeom, H.-S.; Fang, L.-C.; He, S.; Ma, Z.-X.; Kedrowski, B. L.; Hsung, R. P. Ynamides in Ring Forming Transformations. Acc. Chem. Res. 2014, 47, 560−578; (e) Evano, G.; Theunissen, C.; Lecomte, M. Ynamides: Powerful and Versatile Reagents for Chemical Synthesis. Aldrichimica Acta 2015, 48, 59−70; (f) Pan, F.; Shu, C.; Ye, L.-W. Recent Progress Towards Gold-catalyzed Synthesis of N-containing Tricyclic Compounds Based on Ynamides. Org. Biomol. Chem. 2016, 14, 9456−9465. (2) (a) Zificsak, C. A.; Mulder, J. A.; Hsung, R. P.; Rameshkumar, C.; Wei, L.-L. Recent Advances in the Chemistry of Ynamines and Ynamides. Tetrahedron 2001, 57, 7575−7606; (b) Hamada, T.; Ye, X.; Stahl, S. S. Copper-catalyzed Aerobic Oxidative Amidation of Terminal Alkynes: Efficient Synthesis of Ynamides. J. Am. Chem. Soc. 2008, 130, 833−835; (c) Coste, A.; Karthikeyan, G.; Couty, F.; Evano, G. Copper-mediated Coupling of 1,1-Dibromo-1-alkenes with Nitrogen Nucleophiles: a General Method for the Synthesis of Ynamides. Angew. Chem. Int. Ed. 2009, 48, 4381−4385; (d) Yao, B.; Liang, Z.; Niu, T.; Zhang, Y. Iron-Catalyzed Amidation of Alkynyl Bromides: A Facile Route for the Preparation of Ynamides. J. Org. Chem. 2009, 74, 4630−4633; (e) Tu, Y.; Zeng, X.; Wang, H.; Zhao, J. A Robust. One-Step Approach to Ynamides. Org. Lett. 2018, 20, 280−283. (3) Dodd, R. H.; Cariou, K. Ketenimines Generated from Ynamides: Versatile Building Blocks for Nitrogen-Containing Scaffolds. Chem. Eur. J. 2018, 24, 2297−2304.

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(4) For recent examples on gold-catalyzed reaction involving cleavage of C-N bond in ynamides, see: (a) Adcock, H. V.; Langer, T.; Davies, P. W. 1,2-N-Migration in a GoldCatalysed Synthesis of Functionalised Indenes by the 1,1-Carboalkoxylation of Ynamides. Chem. Eur. J. 2014, 20, 7262−7266; (b) Adcock, H. V.; Chatzopoulou, E.; Davies, P. W. Divergent C-H Insertion-Cyclization Cascades of N-Allyl Ynamides. Angew.Chem. Int. Ed. 2015, 54, 15525−15529. (5) The migration of groups from ynamide is promoted by thermal, base and palladium catalysis. Some of the cases it involved N-allyl sulfonamides which produce the corresponding imine product via ynamido--allylpalladium complex. See ref. 1b and 1d for details and references cited therein. (6) (a) Zhu, L.; Yu, Y.; Mao, Z.; Huang, X. Gold-Catalyzed Intermolecular Nitrene Transfer from 2H-azirines to Ynamides: a Direct approach to Polysubstituted Pyrroles. Org. Lett. 2015, 17, 30−33; (b) Wu, Y.; Zhu, L.; Yu, Y.; Luo, X.; Huang, X. Polysubstituted 2-Aminopyrrole Synthesis via Gold-Catalyzed Intermolecular Nitrene Transfer from Vinyl Azide to Ynamide: Reaction Scope and Mechanistic Insights. J. Org. Chem. 2015, 80, 11407−11416; (c) Yu, Y.; Chen, G.; Zhu, L.; Liao, Y.; Wu, Y.; Huang, X. Gold-Catalyzed β-Regioselective Formal [3+2] Cycloaddition of Ynamides with Pyrido[1,2-b]indazoles: Reaction Development and Mechanistic Insights. J. Org. Chem. 2016, 81, 8142−8154; (d) Cheng, X.; Zhu, L.; Lin, M.; Chen, J.; Huang, X. Rapid Access to Cyclopentadiene Derivatives through Gold-Catalyzed Cycloisomerization of Ynamides with Cyclopropenes by Preferential Activation of Alkenes over Alkynes. Chem. Commun. 2017, 53, 3745−3748; (e) Liao, Y.; Lu, Q.; Chen, G.; Yu, Y.; Li, C.; Huang,

X.

Rhodium-Catalyzed

Azide-Alkyne

Cycloaddition

of

Internal

Ynamides:

Regioselective Assembly of 5-Amino-Triazoles under Mild Conditions. ACS Catal. 2017, 7,

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7529−7534; (f) Liao, Y.; Zhu, L.; Yu, Y.; Chen, G.; Huang, X. N-Heterocycle Synthesis via Gold-Catalyzed Intermolecular Nitrene Transfer Reactions of Alkynes. Chin. J. Org. Chem. 2017, 37, 2785−2799; (g) Lin, M.; Zhu, L.; Xia, J.; Yu, Y.; Chen, J.; Mao, Z.; Huang, X. GoldCatalyzed Oxidative Cyclization of Tryptamine Derived Enynamides: A Stereoselective Approach to Tetracyclic Spiroindolines. Adv. Synth. Catal. 2018, 360, 2280−2284. (7) For selected reviews on gold catalysis: (a) Fürstner, A.; Davies, P. W. Catalytic Carbophilic Activation: Catalysis by Platinum and Gold π Acids. Angew. Chem. Int. Ed. 2007, 46, 3410−3449; (b) Hashmi, A. S. K. Gold-Catalyzed Organic Reactions. Chem. Rev. 2007, 107, 3180−3211; (c) Gorin, D. J.; Sherry, B. D.; Toste, F. D. Ligand Effects in Homogeneous Au Catalysis. Chem. Rev. 2008, 108, 3351−3378; (d) Friend, C. M.; Hashmi, A. S. K. Dual gold catalysis. Acc. Chem. Res. 2014, 47, 864−876; (e) Qian, D.; Zhang, J. Gold-Catalyzed Cyclopropanation Reactions Using a Carbenoid Precursor Toolbox. Chem. Soc. Rev. 2015, 44, 677−698; (f) Dorel, R ; Echavarren, A. M. Gold(I)-Catalyzed Activation of Alkynes for the Construction of Molecular Complexity. Chem. Rev. 2015, 115, 9028−9072; (g) Liu, L.; Zhang, J. Gold-Catalyzed Transformations of α-Diazocarbonyl Compounds: Selectivity and Diversity. Chem. Soc. Rev. 2016, 45, 506−516; (h) Pflästerer, D.; Hashmi, A. S. K. Gold Catalysis in Total Synthesis-Recent Achievements. Chem. Soc. Rev. 2016, 45, 1331−1367; (i) Zi, W.; Toste, F. D. Recent Advances in Enantioselective Gold Catalysis. Chem. Soc. Rev. 2016, 45, 4567−4589; (j) Echavarren, A. M.; Hashmi, A. S. K.; Toste, F. D. Gold Catalysis-Steadily Increasing in Importance. Adv. Synth. Catal. 2016, 358, 1347−1347; (k) Wei, Y.; Shi, M. Divergent Synthesis of Carbo- and Heterocycles via Gold-Catalyzed Reactions. ACS Catal. 2016, 6, 2515−2524. (8) For a recent review on gold-catalyzed reactions on diynes and references therein: (a) Asiria, A. M.; Hashmi, A. S. K. Gold-Catalysed Reactions of Diynes. Chem. Soc. Rev. 2016, 45,

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4471−4503; For recent selected examples: (b) Gorin, D. J.; Dubé, P.; Toste, F. D. Synthesis of Benzonorcaradienes by Gold(I)-Catalyzed [4+3] Annulation. J. Am. Chem. Soc. 2006, 128, 14480−14481; (c) Kramer, S.; Madsen, J. L. H.; Rottländer, M.; Skrydstrup, T. Access to 2,5Diamidopyrroles and 2,5-Diamidofurans by Au(I)-Catalyzed Double Hydroamination or Hydration of 1,3-Diynes. Org. Lett. 2010, 12, 2758−2761; (d) Sharp, P. P.; Banwell, M. G.; Renner, J.; Lohmann, K.; Willis, A. C. Consecutive Gold(I)-Catalyzed Cyclization Reactions of o-(Buta-1,3-diyn-1-yl-)-Substituted N-Aryl Ureas: A One-Pot Synthesis of Pyrimido[1,6-a]indol1(2H)-ones and Related Systems. Org. Lett. 2013, 15, 2616−2619; (e) Taguchi, M.; Tokimizu, Y.; Oishi, S.; Fujii, N.; Ohno, H. Synthesis of Fused Carbazoles by Gold-Catalyzed Tricyclization of Conjugated Diynes via Rearrangement of an N-Propargyl Group. Org. Lett. 2015, 17, 6250−6253; (f) Naoe, S.; Yoshida, Y.; Oishi, S.; Fujii, N.; Ohno, H. Total Synthesis of (+)-Conolidine by the Gold(I)-Catalyzed Cascade Cyclization of a Conjugated Enyne. J. Org. Chem. 2016, 81, 5690−5698; (g) Hamada, N.; Yoshida, Y.; Oishi, S.; Ohno, H. Gold-Catalyzed Cascade Reaction of Skipped Diynes for the Construction of a Cyclohepta[b]pyrrole Scaffold. Org. Lett. 2017, 19, 3875−3878; (h) Matsuoka, J.; Matsuda, Y.; Kawada, Y.; Oishi, S.; Ohno, H. Total Synthesis of Dictyodendrins by the Gold-Catalyzed Cascade Cyclization of Conjugated Diynes with Pyrroles. Angew. Chem. Int. Ed. 2017, 56, 7444−7448; (i) Shen, W.-B.; Sun, Q.; Li, L.; Liu, X.; Zhou, B.; Yan, J.-Z.; Lu, X.; Ye, L.-W. Divergent Synthesis of N-heterocycles via Controllable Cyclization of Azido-Diynes Catalyzed by Copper and Gold. Nat. Commun. 2017, 8, 1748; (j) Hamada, N.; Yamaguchi, A.; Inuki, S.; Oishi, S.; Ohno, H. Gold(I)-Catalyzed Oxidative Cascade Cyclization of 1,4-Diyn-3-ones for the Construction of Tropone-Fused Furan Scaffolds. Org. Lett. 2018, 20, 4401−4405.

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(9) For intramolecular hydroarylation of ynamide: (a) Zhang, Y.; Hsung, R. P.; Zhang, X.; Huang, J.; Slafer, B. W.; Davis, A. Brønsted Acid-Catalyzed Highly Stereoselective AreneYnamide Cyclizations. A Novel Keteniminium Pictet-Spengler Cyclization in Total Syntheses of (±)-Desbromoarborescidines A and C. Org. Lett. 2005, 7, 1047−1050; (b) Pan, F.; Liu, S.; Shu, C.; Lin, R.-K.; Yu, Y.-F.; Zhou, J.-M.; Ye, L.-W. Gold-Catalyzed Intermolecular Oxidation of oAlkynylbiaryls: an Easy and Practical Access to Functionalized Fluorenes. Chem. Commun. 2014, 50, 10726−10729; (c) Li, L.; Chen, X.-M.; Wang, Z.-S.; Zhou, B.; Liu, X.; Lu, X.; Ye, L.W. Reversal of Regioselectivity in Catalytic Arene-Ynamide Cyclization: Direct Synthesis of Valuable Azepino[4,5-b]indoles and β-Carbolines and DFT Calculations. ACS Catal. 2017, 7, 4004−4010. (10) For a novel 1,3-sulfonyl shift involving allenesulphonamides and enol ethers: (a) Horino, Y.; Kimura, M.; Wakamiya, Y.; Okajima, T.; Tamaru, Y. Efficient Entry to Tetrahydropyridines: Addition of Enol Ethers to Allenesulfonamides Involving a Novel 1,3-Sulfonyl Shift. Angew. Chem. Int. Ed. 1999, 38, 121−124; (b) Bendikov, M.; Duong, H. M.; Bolanos, E.; Wudl, F. An Unexpected Two-Group Migration Involving a Sulfonynamide to Nitrile Rearrangement. Mechanistic Studies of a Thermal N→C Tosyl Rearrangement. Org. Lett. 2005, 7, 783−786; (c) Nakamura, I.; Yamagishi, U.; Song, D.; Konta, S.; Yamamoto, Y. Gold- and Indium-Catalyzed Synthesis of 3- and 6-Sulfonylindoles from ortho- Alkynyl-N-sulfonylanilines. Angew. Chem. Int. Ed. 2007, 46, 2284−2287; (d) Nakamura, I.; Yamagishi, U.; Song, D.; Konta, S.; Yamamoto, Y. Synthesis of 3- and 6-Sulfonylindoles from ortho-Alkynyl-N-sulfonylanilines by the Use of Lewis Acidic Transition-Metal Catalysts. Chem. Asian J. 2008, 3, 285−295; (e) Yeom, H.-S.; So, E.; Shin, S. Gold-Catalyzed Synthesis of 3-Pyrrolidinones and Nitrones from N-Sulfonyl Hydroxylamines via Oxygen-Transfer Redox and 1,3-Sulfonyl Migration. Chem. Eur. J. 2011,

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17, 1764−1767; (f) Xin, X.; Wang, D.; Li, X.; Wan, B. Highly Regioselective Migration of the Sulfonyl Group: Easy Access to Functionalized Pyrroles. Angew. Chem. Int. Ed. 2012, 51, 1693−1697; (g) Zhu, Y.; Lu, W.-T.; Sun, H.-C.; Zhan, Z.-P. Lewis Base Catalyzed Synthesis of Multisubstituted 4-Sulfonyl-1H-Pyrazole Involving a Novel 1,3-Sulfonyl Shift. Org. Lett. 2013, 15, 4146−4149; (h) Teo, W. T.; Rao, W.; Koh, M. J.; Chan, P. W. H. Gold-Catalyzed Domino Aminocyclization/1,3-Sulfonyl Migration of N-Substituted N-Sulfonyl-aminobut-3-yn-2-ols to 1-Substituted 3-Sulfonyl-1H-pyrroles. J. Org. Chem. 2013, 78, 7508−7517; (i) Wang, B.; Jin, S.; Sun, S.; Cheng, J. Radical Rearrangement of N-sulfonyl-N-aryl Propynamides: Proceeding with Homolytic N-SO2 bond Cleavage and 6-Endo-Dig Cyclization Toward 3-Sulfonyl-2(1H)quinolinones. Org. Chem. Front. 2018, 5, 958−961; (j) Shen, Y.; Li, Q.; Xu, G.; Cui, S. Coupling of Carboxylic Acids with Ynamides and Subsequent Rearrangement for the Synthesis of Imides/Amides. Org. Lett. 2018, 20, 5194−5197; For 1,5-Sulfonyl Migration: (k) Miaskiewicz, S.; Gaillard, B.; Kern, N.; Weibel, J.; Pale, P.; Blanc, A Gold(I)-Catalyzed N-Desulfonylative Amination versus N-to-O 1,5-Sulfonyl Migration: a Versatile Approach to 1-Azabicycloalkanes. Angew. Chem. Int. Ed. 2016, 55, 9088−9092. (l) Prabagar, B.; Mallick, R. K.; Prasad, R.; Gandon, V.; Sahoo, A. K. Umpolung Reactivity of Ynamides: An Unconventional [1,3]-Sulfonyl and

[1,5]-Sulfinyl

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(12) For selected reviews: (a) Handy, S. T.; Zhang, Y. Approaches to the Synthesis of the Lamellarins and Related Natural Products. A review. Organic Preparations and Procedures Int. 2005, 37, 411−445; (b) Nicholasa, G. M.; Phillips, A. Marine Natural Products: Synthetic Aspects. J. Nat. Prod. Rep. 2006, 23, 79−99; (c) Fan, H.; Peng, J.; Hamann, M. T.; Hu, J.-F. Lamellarins and Related Pyrrole-Derived Alkaloids from Marine Organisms. Chem. Rev. 2008, 108, 264−287; (d) Shen, L.; Hu, Y. Recent Advances in the Synthesis of Lamellarins as Anticancer Alkaloids. Chin. J. Org. Chem. 2009, 29, 867−875; (e) Fukuda, T.; Ishibashi, F.; Iwao, M. Synthesis and Biological Activity of Lamellarin Alkaloids: an Overview. Heterocycles 2011, 83, 491−529; (f) Imbri, D.; Tauber, J.; Opatz, T. Synthetic Approaches to the LamellarinsA Comprehensive Review. Mar. Drugs 2014, 12, 6142−6177; For other selected examples: (g) Heim, A.; Terpin, A.; Steglich, W. Biomimetic Synthesis of Lamellarin G. Trimethyl Ether. Angew. Chem. Int. Ed. Engl. 1997, 36, 155−156; (h) Ploypradith, P.; Mahidol, C.; Sahakitpichan, P.; Wongbundit, S.; Ruchirawat, S. A Highly Efficient Synthesis of Lamellarins K and L by the Michael Addition/Ring-Closure Reaction of Benzyldihydroisoquinoline Derivatives with Ethoxycarbonyl-β-nitrostyrenes. Angew. Chem. Int. Ed. 2004, 43, 866−868; (i) Pla, D.; Marchal, A.; Olsen, C. A.; Albericio, F.; Álvarez, M. Modular Total Synthesis of Lamellarin D. J. Org. Chem. 2005, 70, 8231−8234; (j) Fujikawa, N.; Ohta, T.; Yamaguchi, T.; Fukuda, T.; Ishibashi, F.; Iwao, M. Total Synthesis of Lamellarins D, L, and N. Tetrahedron 2006, 62, 594−604; (k) Pla, D.; Marchal, A.; Olsen, C. A.; Francesch, A.; Cuevas, C.; Albericio, F.; Álvarez, M. Synthesis and Structure-Activity Relationship Study of Potent Cytotoxic Analogues of the Marine Alkaloid Lamellarin D. J. Med. Chem. 2006, 49, 3257−3268; (l) Zou, Y.-Q.; Lu, L.-Q.; Fu, L.; Chang, N.J.;

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Pyrrolo[2,1-a]isoquinolines. Angew. Chem. Int. Ed. 2011, 50, 7171−7175; (m) Ueda, K.; Amaike, K.; Maceiczyk, R. M.; Itami, K.; Yamaguchi, J. β-Selective C-H Arylation of Pyrroles Leading to Concise Syntheses of Lamellarins C and I. J. Am. Chem. Soc. 2014, 136, 13226−13232. (13) (a) Quesada, A. R.; García Grávalos, M. D.; Fernández Puentes, J. L. Polyaromatic Alkaloids from Marine Invertebrates as Cytotoxic Compounds and Inhibitors of Multidrug Resistance Caused by P-Glycoprotein. British J. Cancer 1996, 74, 677−682; (b) Palermo, J. A.; Brasco, M. F. R.; Seldes, A. M. Storniamides AD: Alkaloids from a Patagonian Sponge Cliona sp. Tetrahedron 1996, 52, 2727−2734; (c) Ishibashi, F.; Tanabe, S.; Oda, T.; Iwao, M. Synthesis and Structure-Activity Relationship Study of Lamellarin Derivatives. J. Nat. Prod. 2002, 65, 500−504; (d) Bailly, C. Lamellarins, from A to Z: a Family of Anticancer Marine Pyrrole Alkaloids. Curr. Med. Chem. -Anti-Cancer Agents 2004, 4, 363−378; (e) Yamaguchi, T.; Fukuda, T.; Ishibashi, F.; Iwao, M. The First Total Synthesis of Lamellarin α 20-Sulfate, a Selective Inhibitor of HIV-1 Integrase. Tetrahedron Lett. 2006, 47, 3755−3757; (f) Chittchang, M.; Batsomboon, P.; Ruchirawat, S.; Ploypradith, P. Cytotoxicities and Structure-Activity Relationships of Natural and Unnatural Lamellarins toward Cancer Cell Lines. ChemMedChem 2009, 4, 457−465; (g) Bailly, C. Anticancer Properties of Lamellarins. Mar. Drugs 2015, 13, 1105−1123. (14) Recent examples on sulfonyl migration via an intermolecular path: (a) ref.10e; (b) Yu, X.; Xin, X.; Wan, B.; Li, X. Base-Catalyzed Cyclization of N-Sulfonyl Propargylamides to Sulfonylmethyl-Substituted Oxazoles via Sulfonyl Migration. J. Org. Chem. 2013, 78, 4895−4904.

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(15) (a) Teall, M.; Oakley, P.; Harrison, T.; Shaw, D.; Kay, E.; Elliott, J.; Gerhard, U.; Castro, J. L.; Shearman, M.; Ball, R. G.; Tsou, N. N. Aryl sulfones: a New Class of γ-Secretase Inhibitors. Bioorg. Med. Chem. Lett. 2005, 15, 2685−2688; (b) López-Rodríguez, M. L.; Benhamú, B.; de la Fuente, T.; Sanz, A.; Pardo, L.; Campillo, M. A Three-Dimensional Pharmacophore Model for 5-Hydroxytryptamine6 (5-HT6) Receptor Antagonists. J. Med. Chem. 2005, 48, 4216−4219; (c) Smith, D. A.; Jones, R. M. The Sulfonamide Group as a Structural Alert: a Distorted story? Curr. Opin. Drug Discovery Dev. 2008, 11, 72−79; (d) Harrak, Y.; Casula, G.; Basset, J.; Rosell, G.; Plescia, S.; Raffa, D.; Cusimano, M. G.; Pouplana, R.; Pujol, M. D. Synthesis, AntiInflammatory Activity, and in vitro Antitumor Effect of a Novel Class of Cyclooxygenase Inhibitors: 4-(Aryloyl) phenyl methyl Sulfones. J. Med. Chem. 2010, 53, 6560−6571; (e) Ivachtchenko, A. V.; Golovina, E. S.; Kadieva, M. G.; Kysil, V. M.; Mitkin, O. D.; Tkachenko, S. E.; Okun, I. M. Synthesis and Structure-Activity Relationship (SAR) of (5,7-Disubstituted 3phenylsulfonyl-pyrazolo[1,5-a]pyrimidin-2-yl)-methylamines

as

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Serotonin

5-HT6

Receptor (5-HT6R) Antagonists. J. Med. Chem. 2011, 54, 8161−8173. (16) Xia, J.; Shao, A.; Tang, S.; Gao, X.; Gao, M.; Lei, A. Palladium-Catalysed Oxidative Cross-Esterification between two Alcohols. Org. Biomol. Chem. 2015, 13, 6154−6157. (17) CCDC 1816170 (2a) and 1816171 (3f) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.

SYNOPSIS (Word Style “SN_Synopsis_TOC”).

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