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Iridium-Catalyzed Anti-Stereoselective Asymmetric Ring Opening Reactions of Azabenzonorbornadienes with Carboxylic Acids Meina Zhu, Jingchao Chen, Xiaobo He, Cuiping Gu, Jianbin Xu, and Baomin Fan J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.7b00178 • Publication Date (Web): 24 Feb 2017 Downloaded from http://pubs.acs.org on February 24, 2017

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The Journal of Organic Chemistry

Iridium-Catalyzed Anti-Stereoselective Asymmetric Ring Opening Reactions of Azabenzonorbornadienes with Carboxylic Acids Meina Zhu, Jingchao Chen,*, Xiaobo He, Cuiping Gu, Jianbin Xu, and Baomin Fan*, , †

†

†

†

†

†‡

†

YMU-HKBU Joint Laboratory of Traditional Natural Medicine, Yunnan Minzu University, Kunming, Yunnan, People's Republic of China ‡

Key Laboratory of Chemistry in Ethnic Medicinal Resources, Yunnan Minzu University, Kunming, Yunnan 650500,

People's Republic of China

ABSTRACT: The first anti-stereoselective asymmetric ring opening reactions of azabenzonorbornadienes with carboxylic acids had been realized with an iridium catalyst assisted by nBu4NBr. The reaction features in broad substrate scope, good functional group tolerance, allows the synthesis of chiral dihydronaphthalene derivatives with high optical purities.

INTRODUCTION The asymmetric ring-opening (ARO) reaction of heterobicyclic alkenes has been extensively investigated in the past decade as it represents an effective method for the preparation of chiral dihydronaphthalenes, which frequently occur in a broad range of biologically active compounds1 and could be transformed to chiral tetrahydronaphthalenes easily by hydrogenation2. Significant advances toward these reactions have been described by the groups of Lautens and Fagnou followed by Yang and others, and a wide range of nucleophiles such as organometallic reagents,3 amines,4 phenols,5 alcohols6, and organoboronic acids7 were well investigated. Among the heterobicyclic alkenes, as azabenzonorbornadienes are less reactive than corresponding oxabenzonorbornadienes,4c,8 only the ARO reactions of azabenzonorbornadienes with amines and organic zinc reagents were well established in terms of substrate scope and enantioselectivities before our study. By employing Lewis acids as cocatalysts, which have been well studied in the ARO,6a,9 our group has reported a number of highly enantioselective ring-opening reactions of azabenzonorbornadienes by using different nucleophiles.10 Carboxylic acids, which are weaker heteroatom nucleophiles compared with amines and phenols, these applications were limited in the ARO reactions of oxabenzonorbornadienes with moderate efficiency.11 Most recently, our group has disclosed the first syn-stereoselective ARO reactions of azabenzonorbornadienes with carboxylic acids by palladium/silver cocatalysts.12 In this paper, we report the development of an iridium catalytic system that enabled the first antistereoselective asymmetric ring-opening reactions of azabenzonorbornadienes with carboxylic acids, gave the dihydronaphthalenes with high optical purities.

RESULTS AND DISCUSSION Our study of the iridium catalyzed asymmetric ring opening reactions of azabenzonorbornadienes with carboxylic acids commenced with survey of commercially available chiral ligands by using the reaction of azabenzonorbornadiene 1a and benzoic acid 2a. As the experimental results summarized in scheme 1, diphosphine ligands such as (R)BINAP and (R,R)-BDPP failed to promote current reaction. (R)-Phanephos and (R)-MOP gave promising results, with a moderate enantioselectivity by the latter. We then turned our attention to the chiral spiro ligands, and the application of (R)-SIPHOS was found less efficient. We were delight to have observed that high enantioselectivity was obtained by (R)-SDP.13 By increasing the steric demanding on the phosphorus atom, (R)-Tol-SDP and (R)Xyl-SDP have achieved excellent enantioselectivities. Interestingly, (S)-DTB-SIPHOX and (Ra,S,S)-SpiroBOX gave good to high yields but without any chiral control. Therefore, (R)-Xyl-SDP was selected for the further optimization of reaction conditions. In an attempt to improve the yield of present transformation, additives and bases used were investigated (Table 1). Among the Lewis acids, Zn(OTf)2 and CuBr were ineffective (Table 1, entries 2-3). Comparable result was given by FeBr2 (Table 1, entry 4). And the silver salts AgBF4 and AgOTf results in decreased yields and ees (Table 1, entries 5-6). Beside Lewis acids, the organic halide additives such as nBu4NCl, nBu4NBr and nBu4NI were also tested and the use of nBu4NBr increased the yield with the enantioselectivity decreased slightly (Table 1, entries 8-9). In all cases of low yields of the ring opening reactions, only 3aa was observed as product along with 1aa left in the reaction

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mixture. Obviously, the reaction was low efficiency in the absence of an additive (Table 1, entry 10). Previously, the addition of base was proved to be essential as it neutralized the acidic reaction environment and increased the nucleophilicity of the carboxylic acids in this kind of reactions.[11] Thus, the selection of base was taken into consideration by evaluating several organic and inorganic bases. As the experimental results summarized in table 2, DIPA gave a promoted yield but with a lower ee (Table 2, entry 2), DIPEA failed to afford a satisfactory conversion (Table 2, entry 3). No product was detected by using pyridine and piperidine as bases. (Table 2, entries 4-5) Interestingly, by employing a stronger and hindered base, TMP afforded the desired product 3aa with promoted yield and ee (Table 2, entry 6). The using of K2CO3 gave a low yield of the racemic product (Table 2, entry 7). Surprisingly, effort to improve the reaction yield by doubling the catalyst loading lead to a dramatically decreased yield, and more starting materials were left in the reaction mixture (Table 2, entry 8). This lack of react tivity may be ascribed to the coordination of iridium catalyst with benzoic acid. To circumvent this problem, we

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Table 1. Optimization of Reaction Additivesa Boc Boc

N

COOH

NH

[Ir(COD)Cl]2, (R)-xyl-SDP

O

THF, Et3N, additive, 70 oC 2a

1a

Ph O

3aa

Entry

Additive

Time(h)

Yield(%)

Ee(%)b

1

ZnI2

64

32

98

2

Zn(OTf)2

65

trace

---

3

CuBr

65

trace

---

4

FeBr2

65

36

98

5

AgBF4

70

11

82

6

AgOTf

65

17

37

7

n

Bu4NCl

65

14

86

8

n

Bu4NBr

70

41

92

9

n

Bu4NI

70

24

94

10

---

72

25

64

a

Reaction conditions: 1a (0.2 mmol), 2a (1.0 mmol), [Ir(COD)Cl]2 (0.005 mmol), (R)-xyl-SDP (0.012 mmol), additive (0.04 mmol), Et3N (1.2 mmol) in THF (2 mL) at 70 oC for 72 h under an argon atmosphere. bDetermined by HPLC with a Chiralcel OD-H column. Table 2. Further Optimization of Reaction Conditionsa

Entry

Base

Time(h)

Yield(%)

Ee(%)b

1

n

70

41

92

2

DIPA

72

69

68

3

DIPEA

60

34

92

4

pyridine

36

NR

---

5

piperidine

72

NR

---

6

TMP

72

70

94

7

K2CO3

25

10

0

TMP

72

46

93

TMP

65

73

96

TMP

65

76

96

c

8

d

9

10 11 Scheme 1. Screening of various chiral ligands. Reaction conditions: 1a (0.2 mmol), 2a (1.0 mmol), [Ir(COD)Cl]2 (0.005 mmol), chiral ligand (0.012 mmol bidentate ligand or 0.024 mmol monodentate ligand), ZnI2 (0.04 mmol), Et3N (1.2 mmol) in THF (2 mL) at 70 oC for 72 h under an argon atmosphere, ees were determined by chiral HPLC with a Chiralcel OD-H column.

Bu4NBr

e

e,f

12

TMP

65

89

96

---

72

NR

---

a

Reaction conditions: 1a (0.2 mmol), 2a (1.0 mmol), [Ir(COD)Cl]2 (0.005 mmol), (R)-xyl-SDP (0.012 mmol), n Bu4NBr (0.04 mmol), base (1.2 mmol) in THF (2 mL) at 70 oC for 72 h under an argon atmosphere. bDetermined by HPLC with a Chiralcel OD-H column. c[Ir(COD)Cl]2 (0.01 mmol) and (R)-xyl-SDP (0.024 mmol) were used. d 2.5 equivalents of benzoic acid and 3.0 equivalents of

2


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TMP were used. e1.1 equivalents of benzoic acid and 1.3 equivalents of TMP were used. fReacted at 60 oC. (DIPA = diisopropylamine; DIPEA = N,N-diisopropylethylamine; TMP = 2,2,6,6-tetramethylpiperidine). opted to decrease both the amount of benzoic acid and reaction temperature. To our delight, reducing the amount of benzoic to 2.5 and 1.1 equivalents led to an improved yield of 73% and 76% respectively with a promoted enantioselectivity of 96% (Table 2, entries 9-10). As our final piece of optimization, the reaction carried out at 60 o C was found to be optimal (Table 2, entry 11). Finally, the control experiment further confirmed the requirement of a base (Table 2, entry 12). With the further-optimized conditions in hand, a broad range of carboxylic acids were reacted with azabenzonorbornadiene 1a (Scheme 2), and the corresponding ring opening products 3aa-3an were obtained in good to excellent yields (63−98%) with excellent enantioselectivities (92-98%). Electron-rich aryl acids, including p-anisic acid and benzoic acid derivatives that bearing methyl groups at the para-, meta-, and ortho-positions, were converted to the ring opening products 3ab-ae in good yields and excellent ees, indicating steric flexibility in the aryl acids. The absolute configuration of the product 3ad was assigned as 1S,2S by an X-ray crystallographic analysis14 (see supporting information for details). Aryl acids with -F, -Cl, -Br substituents were compatible with the reaction (3afah), 4-nitrobenzoic acid also gave a reasonable yield (3ai). In addition to aryl acids, heterocyclic aromatic acid was also suitable to give the product (3aj). Gratifyingly, all of the tested alkyl acids participated well in present reaction protocol to generate 3ak-an with good results.

Scheme 2. Scope of carboxylic acids. Reaction conditions: 1a (0.2 mmol), 2a (0.26 mmol), [Ir(COD)Cl]2 (0.005 mmol), (R)-xyl-SDP (0.012 mmol), nBu4NBr (0.04 mmol), TMP (0.3 mmol) in THF (2 mL) at 60 oC under an argon atmosphere, ees were determined by chiral HPLC with a Chiralcel OD-H column. Subsequently, various azabenzonorbornadiene derivatives were synthesized and subjected to current reaction procedure to further study its scope (Scheme 3). In general, azabenzonorbornadienes with electron-donating groups were viable substrates, affording the ring opening products in good yields and excellent ees (3ba-ea). But no reaction took place by using dibromo-substituted azabenzonorbornadiene 3f, probably due to the unfavorable electron property. And switching to carbobenzyloxy (Cbz) as protecting group diminished the enantioselectivity (3ga).

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tography was performed with silica gel (200-300 mesh) with petroleum ether and ethyl acetate as eluents.

General procedure for the asymmetric ring opening reactions of azabenzonorbornadienes with carboxylic acids. [Ir(COD)Cl]2 (3.4 mg, 0.005 mmol),

Scheme 3. Scope of azabenzonorbornadienes. Reaction conditions: 1a (0.2 mmol), 2a (0.26 mmol), [Ir(COD)Cl]2 (0.005 mmol), (R)-xyl-SDP (0.012 mmol), n Bu4NBr (0.04 mmol), TMP (0.3 mmol) in THF (2 mL) at 60 oC under an argon atmosphere, ees were determined by chiral HPLC with a Chiralcel OD-H or AS-H column.

CONCLUSION By employing the co-catalytic system comprising [Ir(COD)Cl]2, (R)-xyl-SDP and nBu4NBr, the antistereoselective asymmetric ring opening reactions of azabenzonorbornadienes with carboxylic acids have been realized in moderate to good yields with high enantioselectivities. A wide range of aromatic organic acids and alkyl acids were successfully participate in current methodology, which has offered the straightforward preparation of chiral dihydronaphthalene deravatives.

EXPERIMENTAL SECTION General Method. The reactions and manipulations were performed under an atmosphere of argon by using standard Schlenk techniques and Drybox. Anhydrous THF (Tetrahydrofuran) was distilled from sodium benzophenone 1 13 1 ketyl prior to use. H and C{ H}NMR spectra were recorded at ambient temperature on 400 MHz and 75 MHz spectrometers using tetramethylsilane (TMS) as internal reference. The chemical shifts are quoted in δ units, parts per million (ppm) 1 upﬁeld from the signal of internal TMS. H NMR data is represented as follows: Chemical shift, multiplicity (s = singlet, d = doublet, t = triplet, m = multiplet), integration and coupling constant(s) J in Hertz (Hz). The enantioselective excesses were determined by normal phase HPLC eluted with a mixture of isopropyl alcohol and hexane. High resolution mass spectra (HRMS) were obtained on a double-focusing high resolution magnetic-sector mass-analyzed instrument, operating in an electron impact (EI) mode. Column chroma-

(R)-xyl-SDP (8.4 mg, 0.012 mmol), and 1.0 mL THF were added to a Schlenk tube under an argon atmosphere. The resulting solution was stirred at room temperature for 30 min, n then Bu4NBr (12.8 mg, 0.04 mmol) was added and the mixture was stirred for additional 10 min, then azabenzonorbornadiene 1a-g (0.2 mmol) in THF (1.0 mL) was added, and the mixture was stirred for additional 20 min. After the addition of benzoic acid 2a-n (0.26 mmol), TMP (51 uL, 0.3 mmol) was added, and the mixture was stirred at 60 ℃ under an argon atmosphere with TLC monitoring until the reaction stopped proceed. The reaction mixture was concentrated, and the residue was purified by chromatography on a neutral alumina column to afford the desired product. The enantiomeric excess value of product was determined by HPLC on a chiral OD-H or AS-H column. Characterization Data. (1S,2S)-1-((Tertbutoxycarbonyl)amino)-1,2-dihydronaphthalen-2-yl benzoate (3aa): White solid; hexane/EtOAc = 15/1, 65 mg, 89% yield; o 20 mp = 50–52 C; 96% ee; [α]D = +303.9 (c 0.62, CH2Cl2). The ee of 3aa was determined by HPLC analysis using Daicel Chiralcel OD-H column (25 cm × 0.46 cm ID), conditions: nhexane/i-PrOH = 97/3, 1.0 mL/min, 254 nm; tmajor = 9.58 min, 1 tminor = 12.31 min. H NMR (400 MHz, CDCl3): δ 7.95 (d, J = 7.6 Hz, 2H), 7.46–7.04 (m, 7H), 6.49 (d, J = 9.6 Hz, 1H), 5.99 (d, J = 9.6 Hz, 1H), 5.69 (d, J = 8.8 Hz, 1H), 5.24 (t, J = 9.2 Hz, 1H), 13 1 4.69 (d, J = 8.8 Hz, 1H), 1.27 (s, 9H). C{ H}NMR (CDCl3, 100 MHz): δ 166.4, 155.6, 134.0, 133.1, 132.3, 130.0, 130.0, 128.4, 128.3, 127.1, 126.4, 126.1, 79.9, 73.2, 53.1, 28.3. HRMS (EI) calcd for + C22H23NO4 [M] : 365.1627, found: 365.1628. (1S,2S)-1-((Tert-butoxycarbonyl)amino)-1,2dihydronaphthalen-2-yl 4-methoxybenzoate 4methoxybenzoate (3ab): Colorless oil; hexane/EtOAc = 10/1, 23 66 mg, 84% yield; 96% ee; [α]D = +307.2 (c 0.89, CH2Cl2). The ee of 3ab was determined by HPLC analysis using Daicel Chiralcel OD-H column (25 cm × 0.46 cm ID), conditions: nhexane/i-PrOH = 90/10, 1.0 mL/min, 254 nm; tmajor = 7.94 min, 1 tminor = 10.10 min. H NMR (400 MHz, CDCl3): δ 7.91 (d, J = 7.6 Hz, 2H), 7.32–6.79 (m, 6H), 6.48 (d, J = 9.6 Hz, 1H), 6.00 (d, J = 9.2 Hz, 1H), 5.67 (d, J = 8.8 Hz, 1H), 5.23 (t, J = 9.2 Hz, 1H), 13 1 4.72 (d, J = 9.2 Hz, 1H), 3.75 (s, 3H), 1.29 (s, 9H). C{ H}NMR (CDCl3, 100 MHz): δ 165.1, 162.5, 154.6, 133.0, 131.3, 130.9, 128.7, 127.3, 127.2, 126.0, 125.4, 125.3, 121.3, 112.5, 78.8, 71.9, 54.4, 52.1, + 27.2. HRMS (EI) calcd for C23H25NO5 [M] : 395.1733, found: 395.1746. (1S,2S)-1-((Tert-butoxycarbonyl)amino)-1,2dihydronaphthalen-2-yl 4-methylbenzoate (3ac): Colorless oil; 22 hexane/EtOAc = 15/1, 65 mg, 86% yield; 96% ee; [α]D = +306.6 (c 0.66, CH2Cl2). The ee of 3ac was determined by HPLC analysis using Daicel Chiralcel OD-H column (25 cm × 0.46 cm ID), conditions: n-hexane/i-PrOH = 97/3, 1.0 1 mL/min, 254 nm; tmajor = 10.60 min, tminor = 14.30 min. H NMR (400 MHz, CDCl3): δ 7.92 (d, J = 8.0 Hz, 2H), 7.41–7.13 (m, 6H), 6.57 (d, J = 9.6 Hz, 1H), 6.07 (d, J = 10.0 Hz, 1H), 5.76 (d, J = 8.8 Hz, 1H), 5.32 (t, J = 9.2 Hz, 1H), 4.78 (d, J = 9.6 Hz, 13 1 1H), 2.39 (s, 3H), 1.37 (s, 9H). C{ H}NMR (CDCl3, 100 MHz):

4


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δ 166.5, 155.6, 143.8, 134.0, 132.4, 130.0, 130.0, 129.0, 128.4, 128.3, 127.2, 127.0, 126.3, 79.8, 73.0, 53.1, 28.3, 21.7. HRMS (EI) calcd + for C23H25NO4 [M] : 379.1784, found: 379.1778. (1S,2S)-1-((Tert-butoxycarbonyl)amino)-1,2dihydronaphthalen-2-yl 3-methylbenzoate (3ad): White solid; o hexane/EtOAc = 15/1, 62 mg, 82% yield; mp = 104–106 C; 96% 22 ee; [α]D = +303.4 (c 0.68, CH2Cl2). The ee of 3ad was determined by HPLC analysis using Daicel Chiralcel OD-H column (25 cm × 0.46 cm ID), conditions: n-hexane/i-PrOH = 90/10, 1.0 mL/min, 254 nm; tmajor = 5.45 min, tminor = 6.38 min. 1 HNMR (400 MHz, CDCl3): δ 7.84 (d, J = 8.8 Hz, 2H), 7.42– 7.12 (m, 6H), 6.57 (d, J = 10.0 Hz, 1H), 6.07 (dd, J = 2.8 Hz, 9.6 Hz, 1H), 5.77 (d, J = 8.8 Hz, 1H), 5.33 (t, J = 9.2 Hz, 1H), 4.79 (d, 13 1 J = 9.6 Hz, 1H), 2.37 (s, 3H), 1.37 (s, 9H). C{ H}NMR (CDCl3, 100 MHz): δ 166.6, 155.6, 138.1, 134.0, 133.9, 132.3, 130.4, 129.9, 129.8, 128.4, 128.3, 128.2, 127.1, 127.0, 126.3, 126.3, 79.8, 73.2, 53.1, + 28.3, 21.2. HRMS (EI) calcd for C23H25NO4 [M] : 379.1784, found: 379.1777. (1S,2S)-1-((Tert-butoxycarbonyl)amino)-1,2dihydronaphthalen-2-yl 2-methylbenzoate (3ae): Colorless oil; 20 hexane/EtOAc = 15/1, 70 mg, 92% yield; 94% ee; [α]D = +287.8 (c 0.47, CH2Cl2). The ee of 3ae was determined by HPLC analysis using Daicel Chiralcel OD-H column (25 cm × 0.46 cm ID), conditions: n-hexane/i-PrOH = 95/5, 1.0 1 mL/min, 254 nm; tmajor = 7.29 min, tminor = 8.89 min. H NMR (400 MHz, CDCl3): δ 7.90 (d, J = 7.6 Hz, 1H), 7.40–7.12 (m, 7H), 6.60 (d, J = 10.0 Hz, 1H), 6.10 (dd, J = 3.2, 9.6 Hz, 1H), 5.77 (dd, J = 2.4, 8.4 Hz, 1H), 5.27 (t, J = 8.8 Hz, 1H), 4.80 (d, J 13 1 = 9.2 Hz, 1H), 2.54 (s, 3H), 1.40 (s, 9H). C{ H}NMR (CDCl3, 100 MHz): δ 167.3, 155.5, 140.3, 134.0, 132.2, 132.2, 131.6, 131.1, 130.2, 129.2, 128.5, 128.3, 127.1, 126.7, 126.0, 125.7, 79.9, 72.2, + 53.0, 28.3, 21.8. HRMS (EI) calcd for C23H25NO4 [M] : 379.1784, found: 379.1783. (1S,2S)-1-((Tert-butoxycarbonyl)amino)-1,2dihydronaphthalen-2-yl 4-fluorobenzoate (3af): White solid; o hexane/EtOAc = 12/1, 57 mg, 75% yield; mp = 85–87 C; 96% 22 ee; [α]D = +298.4 (c 0.50, CH2Cl2). The ee of 3af was determined by HPLC analysis using Daicel Chiralcel OD-H column (25 cm × 0.46 cm ID), conditions: n-hexane/i-PrOH = 90/10, 1.0 mL/min, 254 nm; tmajor = 5.45 min, tminor = 6.35 min. 1 H NMR (400 MHz, CDCl3): δ 7.97 (dd, J = 5.6, 8.8 Hz, 2H), 7.34–6.96 (m, 6H), 6.50 (d, J = 10.0 Hz, 1H), 5.98 (dd, J = 3.2, 10.0 Hz, 1H), 5.68 (d, J = 9.2 Hz, 1H), 5.24 (t, J = 9.6 Hz, 1H), 13 1 4.71 (d, J = 9.6 Hz, 1H), 1.29 (s, 9H). C{ H}NMR (CDCl3, 100 MHz): δ 167.1, 165.4, 164.6, 155.6, 133.8, 132.6, 132.5, 132.3, 130.0, 128.4, 128.4, 127.1, 126.3, 126.1, 126.0, 115.6, 115.4, 80.0, 73.5, 53.0, + 28.3. HRMS (EI) calcd for C22H22FNO4 [M] : 383.1533, found: 383.1538. (1S,2S)-1-((Tert-butoxycarbonyl)amino)-1,2dihydronaphthalen-2-yl 4-chlorobenzoate (3ag): White solid; o hexane/EtOAc = 12/1, 63 mg, 79% yield; mp = 90–92 C; 98% 19 ee; [α]D = +302.1 (c 0.66, CH2Cl2). The ee of 3ag was determined by HPLC analysis using Daicel Chiralcel OD-H column (25 cm × 0.46 cm ID), conditions: n-hexane/i-PrOH = 90/10, 1.0 mL/min, 254 nm; tmajor = 5.88 min, tminor = 6.70 min. 1 H NMR (400 MHz, CDCl3): δ 7.97 (d, J = 8.4 Hz, 2H), 7.42– 7.13 (m, 6H), 6.59 (d, J = 10.0 Hz, 1H), 6.06 (dd, J = 3.2, 9.6 Hz, 1H), 5.76 (d, J = 8.8 Hz, 1H), 5.31 (t, J = 9.6 Hz, 1H), 4.75 (d, J = 13 1 9.6 Hz, 1H), 1.37 (s, 9H). C{ H}NMR (CDCl3, 100 MHz): δ 165.5, 155.5, 139.6, 133.8, 132.2, 131.3, 130.2, 128.7, 128.5, 128.4,

127.1, 126.4, 125.8, 80.0, 73.5, 53.0, 28.3. HRMS (EI) calcd for + C22H22ClNO4 [M] : 399.1237, found: 399.1248. (1S,2S)-1-((Tert-butoxycarbonyl)amino)-1,2dihydronaphthalen-2-yl 4-bromobenzoate (3ah): White solid; o hexane/EtOAc = 12/1, 70 mg, 79% yield; mp = 89–91 C; 96% 22 ee; [α]D = +306.3 (c 0.48, CH2Cl2). The ee of 3ah was determined by HPLC analysis using Daicel Chiralcel OD-H column (25 cm × 0.46 cm ID), conditions: n-hexane/i-PrOH = 97/3, 1.0 mL/min, 254 nm; tmajor = 11.98 min, tminor = 14.98 min. 1 H NMR (400 MHz, CDCl3): δ 7.83 (d, J = 7.6 Hz, 2H), 7.49– 7.08 (m, 6H), 6.53 (d, J = 9.6 Hz, 1H), 6.00 (d, J = 9.6 Hz, 1H), 5.69 (d, J = 8.8 Hz, 1H), 5.24 (t, J = 9.2 Hz, 1H), 4.65 (d, J = 9.6 13 1 Hz, 1H), 1.30 (s, 9H). C{ H}NMR (CDCl3, 100 MHz): δ 165.6, 155.6, 133.8, 132.2, 131.7, 131.4, 130.1, 128.8, 128.5, 128.4, 128.3, 127.1, 126.4, 125.8, 80.0, 73.6, 53.0, 28.3. HRMS (EI) calcd for + C22H22BrNO4 [M] : 443.0732, found: 443.0737. (1S,2S)-1-((Tert-butoxycarbonyl)amino)-1,2dihydronaphthalen-2-yl 4-nitrobenzoate (3ai): White solid; o hexane/EtOAc = 10/1, 57 mg, 63% yield; mp = 105-107 C; 98% 22 ee; [α]D = +356.5 (c 0.67, CH2Cl2). The ee of 3ai was determined by HPLC analysis using Daicel Chiralcel OD-H column (25 cm × 0.46 cm ID), conditions: n-hexane/i-PrOH = 90/10, 1.0 mL/min, 254 nm; tmajor = 11.78 min, tminor = 15.34 1 min. HNMR (400 MHz, CDCl3): δ 8.26–8.19 (m, 4H), 7.43– 7.15 (m, 4H), 6.63 (d, J = 9.6 Hz, 1H), 6.08 (dd, J = 3.2, 10.0 Hz, 1H), 5.80 (d, J = 1.6 Hz, 1H), 5.33 (t, J = 8.8 Hz, 1H), 4.79 (d, J = 13 1 9.6 Hz, 1H), 1.38 (s, 9H). C{ H}NMR (CDCl3, 100 MHz): δ 164.4, 155.5, 150.6, 135.3, 133.4, 132.1, 131.0, 130.6, 128.7, 128.6, 127.3, 126.5, 125.0, 123.5, 80.1, 74.3, 52.8, 28.3. HRMS (EI) calcd + for C22H22N2O6 [M] : 410.1478, found: 410.1480. (1S,2S)-1-((Tert-butoxycarbonyl)amino)-1,2dihydronaphthalen-2-yl thiophene-2-carboxylate (3aj): White o solid, hexane/EtOAc = 10/1, 50 mg, 68% yield; mp = 47–49 C; 22 98% ee. [α]D = +266.3 (c 0.48, CH2Cl2). The ee of 3aj was determined by HPLC analysis using Daicel Chiralcel OD-H column (25 cm × 0.46 cm ID), conditions: n-hexane/i-PrOH = 90/10, 1.0 mL/min, 254 nm; tmajor = 6.57 min, tminor = 7.76 1 min. HNMR (400 MHz, CDCl3): δ 7.80 (d, J = 3.2 Hz, 1H), 7.55–7.06 (m, 6H), 6.59 (d, J = 9.6 Hz, 1H), 6.07 (d, J = 9.2 Hz, 1H), 5.75 (d, J = 8.8 Hz, 1H), 5.28 (t, J = 9.2 Hz, 1H), 4.76 (d, J = 13 1 9.2 Hz, 1H), 1.37 (s, 9H). C{ H}NMR (CDCl3, 100 MHz): δ 162.0, 155.5, 134.0, 133.9, 133.5, 132.8, 132.2, 130.1, 128.4, 128.3, 127.7, 127.1, 126.5, 125.8, 79.9, 73.2, 53.1, 28.2. HRMS (EI) calcd + for C20H21NO4S [M] : 371.1191, found: 371.1203. (1S,2S)-1-((Tert-butoxycarbonyl)amino)-1,2dihydronaphthalen-2-yl acetate (3ak): White solid; hexo ane/EtOAc = 10/1, 57 mg, 95% yield;mp = 68–70 C; 94% ee; 20 [α]D = +233.3 (c 0.07, CH2Cl2). The ee of 3ak was determined by HPLC analysis using Daicel Chiralcel OD-H column (25 cm × 0.46 cm ID), conditions: n-hexane/i-PrOH = 90/10, 1.0 1 mL/min, 254 nm; tmajor = 5.34 min, tminor = 6.12 min. HNMR (400 MHz, CDCl3): δ 7.37–7.10 (m, 4H), 6.56 (d, J = 10.0 Hz, 1H), 5.98 (dd, J = 3.6, 10.0 Hz, 1H), 5.53 (dd, J = 2.8, 7.6 Hz, 1H), 5.07 (t, J = 8.8 Hz, 1H), 4.72 (d, J = 8.8 Hz, 1H), 2.05 (s, 13 1 3H), 1.46 (s, 9H). C{ H}NMR (CDCl3, 100 MHz): δ 170.7, 155.5, 133.7, 132.0, 130.2, 128.5, 128.4, 127.1, 127.0, 125.5, 79.9, 71.6, 52.7, + 28.3, 21.1. HRMS (EI) calcd for C17H21NO4 [M] : 303.1471, found: 303.1475. (1S,2S)-1-((Tert-butoxycarbonyl)amino)-1,2dihydronaphthalen-2-yl propionate (3al): White solid; hexo ane/EtOAc = 15/1, 58 mg, 92% yield; mp = 105–107 C; 94% ee.

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The Journal of Organic Chemistry 22

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[α]D = +183.3 (c 0.63, CH2Cl2). The ee of 3al was determined by HPLC analysis using Daicel Chiralcel OD-H column (25 cm × 0.46 cm ID), conditions: n-hexane/i-PrOH = 90/10, 1.0 1 mL/min, 254 nm; tmajor = 4.77 min, tminor = 5.60 min. HNMR (400 MHz, CDCl3): δ 7.36–7.10 (m, 4H), 6.55 (d, J = 9.6 Hz, 1H), 5.79 (dd, J = 3.6, 10.0 Hz, 1H), 5.56 (dd, J = 2.8, 8.4 Hz, 1H), 5.08 (t, J = 8.8 Hz, 1H), 4.71 (d, J = 8.8 Hz, 1H), 2.36–2.30 13 1 (m, 2H), 1.46 (s, 9H), 1.13 (t, J = 7.6 Hz, 3H). C{ H}NMR (CDCl3, 100 MHz): δ 174.2, 155.5, 133.8, 132.1, 130.0, 128.4, 128.3, 127.0, 126.8, 125.8, 79.8, 71.5, 52.8, 28.3, 9.08. HRMS (EI) calcd + for C18H23NO4 [M] : 317.1627, found: 317.1628. (1S,2S)-1-((Tert-butoxycarbonyl)amino)-1,2dihydronaphthalen-2-yl isobutyrate (3am): White solid, hexo ane/EtOAc = 15/1, 61 mg, 92% yield; mp = 83-85 C; 94% ee. 22 [α]D = +166.9 (c 0.44, CH2Cl2). The ee of 3am was determined by HPLC analysis using Daicel Chiralcel OD-H column (25 cm × 0.46 cm ID), conditions: n-hexane/i-PrOH = 90/10, 1.0 mL/min, 254 nm; tmajor = 4.20 min, tminor = 4.96 min. 1 HNMR (400 MHz, CDCl3): δ 7.34–7.09 (m, 4H), 6.54 (d, J = 9.6 Hz, 1H), 5.93 (dd, J = 3.2, 10.0 Hz, 1H), 5.59–5.55 (m, 1H), 5.11 (t, J = 9.6 Hz, 1H), 4.73 (d, J = 9.2 Hz, 1H), 2.61–2.50 (m, 13 1 1H), 1.46 (s, 9H), 1.18–1.14 (m, 6H). C{ H}NMR (CDCl3, 100 MHz): δ 177.0, 155.5, 134.1, 132.2, 129.8, 128.4, 128.2, 127.0, 126.4, 126.1, 79.8, 71.6, 53.1, 34.0, 28.4, 19.0, 18.8. HRMS (EI) calcd for + C19H25NO4 [M] : 331.1784, found: 331.1777. (1S,2S)-1-((Tert-butoxycarbonyl)amino)-1,2dihydronaphthalen-2-yl butyrate (3an): Colorless oil; hex22 ane/EtOAc = 15/1, 61 mg, 92% yield; 94% ee; [α]D = +189.4 (c 0.45, CH2Cl2). The ee of 3an was determined by HPLC analysis using Daicel Chiralcel OD-H column (25 cm × 0.46 cm ID), conditions: n-hexane/i-PrOH = 90/10, 1.0 mL/min, 254 1 nm; tmajor = 4.48 min, tminor = 5.30 min. HNMR (400 MHz, CDCl3): δ 7.35–7.10 (m, 4H), 6.55 (d, J = 10.0 Hz, 1H), 5.96 (dd, J = 3.2, 10.0 Hz, 1H), 5.58–5.55 (m, 1H), 5.08 (t, J = 8.8 Hz,1H), 4.74 (d, J = 9.2 Hz, 1H), 2.29 (t, J = 7.2 Hz, 2H), 1.69–1.59 (m, 13 1 2H), 1.46 (s, 9H), 0.93 (t, J = 7.6 Hz, 3H). C{ H}NMR (CDCl3, 100 MHz): δ 173.4, 155.5, 133.9, 132.1, 130.0, 128.4, 128.3, 127.0, 126.7, 125.9, 79.8, 71.4, 52.9, 36.2, 28.3, 18.4, 13.6. HRMS (EI) + calcd for C19H25NO4 [M] : 331.1784, found: 331.1791. (1S,2S)-1-((Tert-butoxycarbonyl)amino)-6,7-dimethyl-1,2dihydronaphthalen-2-yl benzoate (3ba): White solid; hexo ane/EtOAc = 12/1, 67 mg, 86% yield; mp = 117–119 C; 96% ee; 20 [α]D = +310.4 (c 0.16, CH2Cl2). The ee of 3ba was determined by HPLC analysis using Daicel Chiralcel OD-H column (25 cm × 0.46 cm ID), conditions: n-hexane/i-PrOH = 90/10, 1.0 1 mL/min, 254 nm; tmajor = 5.83 min, tminor = 6.25 min. HNMR (400 MHz, CDCl3): δ 8.03 (d, J = 7.6 Hz, 2H), 7.54–6.91 (m, 5H), 6.54 (d, J = 9.6 Hz, 1H), 6.02 (dd, J = 3.2, 10.0 Hz, 1H), 5.72 (t, J = 2.0 Hz, 1H), 5.24 (t, J = 8.8 Hz, 1H), 4.71 (d, J = 9.2 13 1 Hz, 1H), 2.27 (s, 3H), 2.24 (s, 3H), 1.37 (s, 9H). C{ H}NMR (CDCl3, 100 MHz): δ 166.4, 155.6, 136.9, 136.5, 133.1, 131.2, 130.1, 130.0, 129.9, 128.5, 128.3, 128.0, 124.8, 79.8, 73.2, 52.7, 28.3, 19.8, + 19.4. HRMS (EI) calcd for C24H27NO4 [M] : 393.1940, found: 393.1955. (1S,2S)-1-((Tert-butoxycarbonyl)amino)-6,7-dimethoxy-1,2dihydronaphthalen-2-yl benzoate (3ca): White solid; hexo ane/EtOAc = 10/1, 66 mg, 78% yield; mp = 76–78 C; 94% ee; 22 [α]D = +80.0 (c 0.08, CH2Cl2). The ee of 3ca was determined by HPLC analysis using Daicel Chiralcel AS-H column (25 cm × 0.46 cm ID), conditions: n-hexane/i-PrOH = 90/10, 1.0 1 mL/min, 254 nm; tmajor = 14.81 min, tminor = 27.51 min. HNMR

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(400 MHz, CDCl3): δ 8.00 (d, J = 7.6 Hz, 2H), 7.55–6.69 (m, 5H), 6.54 (d, J = 9.6 Hz, 1H), 6.03 (d, J = 9.2 Hz, 1H), 5.69 (s, 1H), 5.18 (t, J = 8.4 Hz, 1H), 4.72 (d, J = 9.2 Hz, 1H), 3.93 (s, 13 1 3H), 3.89 (s, 3H), 1.39 (s, 9H). C{ H}NMR (CDCl3, 100 MHz): δ 166.2, 155.5, 149.0, 148.7, 133.1, 130.2, 130.0, 129.9, 128.3, 126.5, 125.0, 123.3, 110.7, 110.5, 80.0, 72.3, 56.1, 56.0, 52.4, 28.3. HRMS + (EI) calcd for C24H27NO6 [M] : 425.1838, found: 425.1840. (5S,6S)-5-((Tert-butoxycarbonyl)amino)-5,6dihydronaphtho[2,3-d][1,3]dioxol-6-yl benzoate (3da): White o solid; hexane/EtOAc = 10/1, 72 mg, 88% yield; mp = 61–63 C; 22 96% ee; [α]D = +323.4 (c 0.22, CH2Cl2). The ee of 3da was determined by HPLC analysis using two Daicel Chiralcel ODH columns (25 cm × 0.46 cm ID), conditions: n-hexane/iPrOH = 98/2, 0.5 mL/min, 254 nm; tmajor = 23.39 min, tminor = 1 26.52 min. HNMR (400 MHz, CDCl3): δ 8.01 (d, J = 7.6 Hz, 2H), 7.55–6.63 (m, 5H), 6.47 (d, J = 9.6 Hz, 1H), 6.00 (d, J = 10.0 Hz, 1H), 5.96 (d, J = 4.0 Hz, 2H), 5.69 (d, J = 6.8 Hz, 1H), 5.18 (t, J = 8.8 Hz, 1H), 4.75 (d, J = 9.2 Hz, 1H), 1.37 (s, 9H). 13 1 C{ H}NMR (CDCl3, 100 MHz): δ 166.3, 155.5, 147.5, 147.4, 133.1, 130.0, 129.9, 129.9, 126.4, 123.7, 107.9, 107.7, 101.3, 79.9, 72.7, + 52.9, 28.3. HRMS (EI) calcd for C23H23NO6 [M] : 409.1525, found: 409.1530. (6S,7S)-6-((Tert-butoxycarbonyl)amino)-2,3,6,7tetrahydronaphtho [2,3-b][1,4]dioxin-7-yl benzoate (3ea): White solid; hexane/EtOAc = 10/1, 69 mg, 81% yield; mp = o 22 105–107 C; 96% ee; [α]D = +278.3 (c 0.55, CH2Cl2). The ee of 3ea was determined by HPLC analysis using Daicel Chiralcel two OD-H columns (25 cm × 0.46 cm ID), conditions: nhexane/i-PrOH = 98/2, 0.5 mL/min, 254 nm; tmajor = 79.66 1 min, tminor = 93.18 min. HNMR (400 MHz, CDCl3): δ 7.95 (d, J = 7.2 Hz, 2H), 7.47–6.58 (m, 5H), 6.37 (d, J = 10.0 Hz, 1H), 5.89 (dd, J = 3.2, 10.0 Hz, 1H), 5.62 (dd, J = 1.6, 8.8 Hz, 1H), 5.11 (t, J = 9.2 Hz, 1H), 4.68 (d, J = 9.6 Hz, 1H), 4.17 (s, 4H), 1.28 (s, 13 1 9H). C{ H}NMR (CDCl3, 100 MHz): δ 166.4, 155.5, 143.3, 143.1, 133.1, 130.0, 129.9, 129.4, 128.3, 127.5, 126.1, 124.3, 116.1, 116.0, 79.8, 73.1, 64.5, 64.4, 52.6, 28.3. HRMS (EI) calcd for + C24H25NO6 [M] : 423.1682, found: 423.1684. (1S,2S)-1-(((Benzyloxy)carbonyl)amino)-1,2dihydronaphthalen-2-yl benzoate (3ga): White solid; hexo ane/EtOAc = 15/1, 66 mg, 83% yield; mp = 146–148 C; 40% ee; 22 [α]D = +301.3 (c 0.15, CH2Cl2). The ee of 3ga was determined by HPLC analysis using Daicel Chiralcel OD-H column (25 cm × 0.46 cm ID), conditions: n-hexane/i-PrOH = 90/10, 0.5 1 mL/min, 254 nm; tmajor = 30.79 min, tminor = 34.58min. HNMR (400 MHz, CDCl3): δ 7.93 (d, J = 7.2 Hz, 2H), 7.48–7.04 (m, 12H), 6.50 (d, J = 9.6 Hz, 1H), 5.99 (d, J = 10.0 Hz, 1H), 5.72 (d, J = 8.4 Hz, 1H), 5.29 (t, J = 9.2 Hz, 1H), 5.00 (m, 3H). 13 1 C{ H}NMR (CDCl3, 100 MHz): δ 166.3, 156.3, 136.2, 133.4, 133.2, 132.2, 130.2, 130.0, 129.8, 129.7, 128.5, 128.5, 128.4, 128.3, 128.1, 128.0, 127.2, 126.5, 125.8, 72.6, 67.0, 53.6, 29.7. HRMS (EI) + calcd for C25H21NO4 [M] : 399.1471, found: 399.1487.

ASSOCIATED CONTENT Supporting Information 1

13

Copies of H and C NMR spectra of products, HPLC spectra of products, and X-ray crystallographic data (ORTEP) of 3ad.

AUTHOR INFORMATION

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Corresponding Author

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*E-mail of J. C. Chen: [email protected] *E-mail of B. M. Fan: [email protected]

Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT We thank the National Natural Science Foundation of China (21572198, 21362043, 21302162) and the Department of Education of Yunnan Province (ZD2015012) for financial support.

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