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Cycloaddition of Fluorenone N-Aryl Nitrones with Methylenecyclopropanes and Sequential [1,3]-Rearrangement: An Entry to Synthesis of Spirofluoenylpiperidin-4-ones Xiao-Pan Ma, Jie-Feng Zhu, Si-Yi Wu, Chun-Hua Chen, Ning Zou, Cui Liang, Gui-Fa Su, and Dong-Liang Mo J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.6b02544 • Publication Date (Web): 16 Dec 2016 Downloaded from http://pubs.acs.org on December 18, 2016

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The Journal of Organic Chemistry

Cycloaddition

of

Fluorenone

N-Aryl

Nitrones

with

Methylenecyclopropanes and Sequential [1,3]-Rearrangement: An Entry to Synthesis of Spirofluoenylpiperidin-4-ones Xiao-Pan Ma, Jie-Feng Zhu, Si-Yi Wu, Chun-Hua Chen, Ning Zou, Cui Liang, Gui-Fa Su*, and Dong-Liang Mo* State Key Laboratory for Chemistry and Molecular Engineering of Medicinal Resources, Ministry of Science and Technology of China; School of Chemistry & Pharmaceutical Sciences, Guangxi Normal University, 15 Yu Cai Road, Guilin 541004, China. Ar R1

R3

N O

1

R

O

Ar N

R3 R2

R2

1,3-dipolar cycloaddition 1,3-rearrangement 15 examples 46-87% yields

ABSTRACT：： A facile synthesis of various spirofluorenylpiperidin-4-ones has been achieved in good yields from fluorenone N-aryl nitrones and methylenecyclopropanes. This

method

involved

5-spirocyclopropane-isoxazoline,

an

initial which

cycloaddition underwent

a

to highly

form

a

selective

1,3-rearrangement to give the desired product. The stereochemistry of the spirofluorenylpiperidin-4-one could be controlled by the cycloaddition and sequential rearrangement strategy. Furthermore, the spirofluorenylpiperidin-4-ones could be not only prepared in one-pot procedure but also converted to useful scaffolds by reduction or oxidation conditions.

ACS Paragon Plus Environment


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INTRODUCTION The development of new and efficient methods for synthesis of piperidinone derivatives represents an important research field because these piperidinone scaffolds showed the unique biological activities and served as valuable intermediates in organic synthesis.1,2 1,3-Dipolar cycloaddition of nitrones to the double bond of methylenecyclopropanes is one of the most extensively studied cycloaddition reactions due to the rich chemistry of 5-spirocyclopropane-isoxazoline cycloadducts formed in the reactions.3,4 5-Spirocyclopropane-isoxazolines could undergo Brandi-Guarna rearrangement to afford piperidin-4-ones or related compounds because of the highly strained spirocyclopropane ring.5 In 1989, Brandi and coworkers

found

that

methylenecyclopropane

the could

reaction form

of

(Z)-N-aryl

aldonitrones

and

4-spirocyclopropane-isoxazoline

and

5-spirocyclopropane-isoxazoline which could be converted to a mixture of enamine, piperidin-4-one and benzoazocinone (Scheme 1-A).6 A further study on the regioselective formation of 5-spirocyclopropane-isoxazoline and its 1,3- or 3,3-rearrangement was reported by Molchanov and coworkers (Scheme 1-B).7 The effect of substituted groups on both nitrones and methylenecyclopropanes to the N-O bond

rearrangement

was

studied.

Although

the

rearrangement

of

5-spirocyclopropane-isoxazoline has been studied, the yields and selectivities observed in the 1,3- and 3,3-rearrangement of 5-spirocyclopropane-isoxazoline are generally poor for N-aryl nitrones. During the studies on the rearrangement of N-O bond in our group,8 we envisaged that methylenecyclopropanes bearing an


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alkoxycarbonyl group would regioselectively react with N-aryl nitrones bearing a rigid

and

sterically

encumbered

9-fluorenyl

group

to

give

5-spirocyclopropane-isoxazolines, which might undergo a controllable rearrangement process. Fluorenone nitrones are distinct from traditional nitrones because the rigidity and steric hindrance of the fluorene.9 This property can be exploited by N-O bond cleavage10 to afford spirofluorenylpiperidinones that exhibits privileged scaffolds present in bioactive pharmaceuticals and organic materials.11 Herein, we reported a facile synthesis of spirofluorenylpiperidin-4-ones in good yields from fluorenone nitrones and methylenecyclopropanes (MCP) (Scheme 1-C). A) Brandi' work, mixture of [3,3]- and [1,3]-rearrangement Ph

O

N

Ph

Ph +

N O Ph 20% O

Ph

PhHN

O 14% O

H

+ Ph

N

N H Ph 14%

Ph 35%

B) Molchanov's work, substituted groups effect on [3,3]- and [1,3]-rearrangement CO 2Me Ph

N

R

O CO 2Me R

CO 2Me CO2Me N R R 2-54% yield

R = Ph, CO2 Me

+

R R

OH CO2 Me N Ph

CO2 Me

10-16% yield

C) This work, high selective [1,3]-rearrangement Ar

O CO 2R Ar N

N O

O

Ar N

O OH

OR only observed

Scheme 1. The rearrangement of N-O cyclopropane intermediates RESULTS and DISCUSSION We initially evaluated the formation of 5-spirocyclopropane-isoxazoline via the cycloaddition reaction of N-aryl fluorenone nitrone and methylenecyclopropane. N-Phenyl fluorenone nitrone 1a and methylenecyclopropane 2a were chosen as model



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substrates for this reaction. As shown in Table 1, the desired cycloadduct 3a was isolated in excellent yield from a variety of different solvents, including toluene, 1,2-dichloroethane (DCE), MeCN, THF, DMSO and MeOH following 18−24 h at 40 °C (Table 1, entries 1–6). Reducing the reaction temperature to room temperature led to an increase in the yield of 3a to 99%, albeit after extending the reaction time to 36 h (Table 1, entry 7). In contrast, increasing the reaction temperature to 60 °C led to a decrease in the yield of 3a (Table 1, entry 8). Furthermore, no product 3a was observed when the reaction was conducted at 80 °C, with the starting materials 1a and 2a being recovered unchanged (Table 1, entry 9). Table 1. Optimization of the Cycloaddition Reaction Conditions.a Ph

N

Ph

O

O +

O

conditions

Ph

O N

O

Ph

O 1a

2a

entry

solvent

T (°C)

3a,yield%b

1

toluene

40

98

2

DCE

40

98

3

MeCN

40

96

4

THF

40

97

5

DMSO

40

79

6

MeOH

40

94

7

DCE

25

99c

8

DCE

60

84

3a


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9 a

DCE

80

7.0. A white solid appeared and the mixture was stirred for 30 min before CH2Cl2 (50 mL)


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was added. The organic layer was separated and washed with brine (50 mL) and dried over MgSO4. The filtrate was concentrated to give ylide as a white solid which was used directly without further purification for the next step. To a refluxing solution of ylide (10 mmol) and benzoic acid (122 mg, 10 mmol%) in benzene (50 mL) was added (1-ethoxycyclopropoxy)trimethylsilane (2 mL, 10 mmol) via syringe. After addition was completed, the mixture was allowed to reflux at 80 ºC for 18 h. And then cooling to room temperature, benzene was removed under reduced pressure and the crude product was purified by flash chromatography (the crude residue was dry loaded on silica gel; 1:100−1:20 ethyl acetate:petroleum ether) to afford methylenecyclopropane 2 as a colorless oil. The methylenecyclopropane 2d18, 2e19, 2f19, 2g19, 2h20, 2i21, 2j22, 2k23 were prepared according to literature methods and their spectral data matched literature values. Cinnamyl-2-cyclopropylideneacetate (2a), a colorless oil, 1.490 g, 69% yield. 1H NMR (400 MHz; CDCl3): δ 7.33 (d, J = 7.2 Hz, 2H), 7.27−7.23 (m, 2H), 7.20−7.16 (m, 1H), 6.63 (d, J = 16.0, 1H), 6.30−6.21 (m, 2H), 4.77 (d, J = 6.0, 2H), 1.44−1.39 (m, 2H), 1.21−1.16 (m, 2H);

13

C NMR (100 MHz, CDCl3): δ 165.8, 145.7, 136.3,

133.7, 128.5, 127.9, 126.5, 123.5, 110.7, 64.7, 4.6, 2.1; IR (thin film) 3031, 2988, 2881, 1713, 1601, 1494, 1170, 741, 695 cm−1; HRMS (EI) m/z calcd for C14H14O2Na (M+Na)+ 237.0891, found 237.0887. (E)-2-Methyl-3-phenylallyl-2-cyclopropylideneacetate (2b), a colorless oil, 0.800 g, 35% yield. 1H NMR (400 MHz; CDCl3): δ 7.36−7.32 (m, 2H), 7.29−7.23 (m, 3H),



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6.57 (s, 1H), 6.30 (s, 1H), 4.73 (s, 2H), 1.92 (s, 3H), 1.48−1.46 (m, 2H), 1.28−1.24 (m, 2H); 13C NMR (100 MHz, CDCl3): δ 165.8, 145.5, 137.1, 133.0, 128.9, 128.1, 127.7, 126.6, 110.8, 69.6, 15.5, 4.6, 2.2; IR (thin film) 3056, 2981, 2872, 1716, 1600, 1491, 1254, 746, 699 cm−1; HRMS (EI) m/z calcd for C15H16O2Na (M+Na)+ 251.1048, found 251.1045. 3-Phenylprop-2-ynyl-2-cyclopropylideneacetate (2c), a colorless oil, 1.200 g, 57% yield. 1H NMR (400 MHz; CDCl3): δ 7.46−7.44 (m, 2H), 7.32−7.26 (m, 3H), 6.30 (s, 1H), 5.00 (s, 2H), 1.52−1.48 (m, 2H), 1.30−1.24 (m, 2H);

13

C NMR (100 MHz,

CDCl3): δ 165.2, 146.8, 131.8, 128.6, 128.2, 122.2, 110.1, 86.1, 83.2, 52.4, 4.7, 2.2; IR (thin film) 3060, 2985, 2875, 1718, 1600, 1490, 1252, 759, 692 cm−1; HRMS (EI) m/z calcd for C14H12O2Na (M+Na) + 235.0735, found 235.0732. ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website. Spectra of compounds 1, 2, 3, 4, 5, and 6 (PDF), chromatograms of 3aj and 4a (PDF) AUTHOR INFORMATION Corresponding Author * E-mail: [email protected] * E-mail: [email protected] Notes The authors declare no competing financial interest.


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ACKNOWLEDGMENT Financial support from the “Overseas 100 Talents Program” of Guangxi Higher Education and State Key Laboratory for Chemistry and Molecular Engineering of Medicinal Resources (Guangxi Normal University), Ministry of Science and Technology of China (CMEMR2015-A05, CMEMR2014-A01), National Natural Science Foundation of China (21562005, 21602037, 21462008), and Natural Science Foundation of Guangxi (2015GXNSFCA139001, 2016GXNSFFA380005) are greatly appreciated. REFERENCES (1) Some studies on bioactivity of piperidinones: (a) Das, U.; Pati, H. N.; Baráth, Z.; Csonka, Á.; Molnál, J.; Dimmock, J. R. Bioorg. Med. Chem. Lett. 2016, 26, 1319; (b) Chen, D. H.; Valente, S.; Castellano, S.; Sbardella, G.; Di Santo, R.; Costi, R.; Bedford, M. T.; Mai, A. J. Med. Chem. 2011, 54, 4928; (c) Das, U.; Pati, H. N.; Sakagami, H.; Hashimoto, K.; Kawase, M.; Balzarini, J.; De Clercq, E.; Dimmock, J. R. J. Med. Chem. 2011, 54, 3445; (d) Michelsen, K.; Jordan, J. B.; Lewis, J.; Long, A. M.; Yang, E.; Rew, Y.; Zhou, J.; Yakowec, P.; Schnier, P. D.; Huang, X.; Poppe, L. J. Am. Chem. Soc. 2012, 134, 17059. (2) Some transformations for piperidinones: (a) Peng, Z. H.; Wong, J. W.; Hansen, E. C.; Puchlopek-Dermenci, A. L. A.; Clarke, H. J. Org. Lett. 2014, 16, 860; (b) Lee, C. W.; Lira, R.; Dutra, J.; Ogilvie, K.; O’Neill, B. T.; Brodney, M.; Helal, C.; Young, J.; Lachapelle, E.; Sakya, S.; Murray, J. C. J. Org. Chem. 2013, 78, 2661; (c) Ellis, G. L.; Amewu, R.; Sabbani, S.; Stocks, P. A.; Shone, A.; Stanford, D.; Gibbons, P.; Avies,



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