Regiocontrol of the [2 + 2] Photodimerization in the Solid State Using

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Regiocontrol of the [2+2] Photodimerization in the Solid State using Isosteric Resorcinols: Head-to-Tail Cyclobutane Formation via Unexpected Embraced Assemblies Devin P. Ericson, Zachary P. Zurfluh-Cunningham, Ryan Groeneman, Elizabeth Elacqua, Eric Reinheimer, Bruce C. Noll, and Leonard R. MacGillivray Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.5b00939 • Publication Date (Web): 21 Oct 2015 Downloaded from http://pubs.acs.org on October 24, 2015

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Crystal Growth & Design

Regiocontrol of the [2+2] Photodimerization in the Solid State using Isosteric Resorcinols: Head-to-Tail Cyclobutane Formation via Unexpected Embraced Assemblies

Devin P. Ericson,a Zachary P. Zurfluh-Cunningham,a Ryan H. Groeneman,a* Elizabeth Elacqua,b Eric W. Reinheimer,c Bruce C. Noll,d and Leonard R. MacGillivrayb* a. Department of Biological Sciences, Webster University, St. Louis, MO 63119 b. Department of Chemistry, University of Iowa, Iowa City, IA 52242 c. Department of Chemistry and Biochemistry, W.M. Keck Foundation Center for Molecular Structure, California State University San Marcos, San Marcos, CA 92096 d. Bruker AXS Inc., 5465 East Cheryl Parkway, Madison, WI 53711 Email: [email protected], Tel: +1 314-246-7466 Email: [email protected], Fax: +1 319-335-1270; Tel: +1 319-335-3504

Abstract Regiocontrolled head-to-head and head-to-tail [2+2] photodimerizations of (E)-methyl-3(pyridin-3-yl)prop-2-enoate are achieved in the solid state using 4,6-di-X-res (where: X = Cl, Br, I; res = resorcinol) as small-molecule templates. The components in each co-crystal form discrete, three-component supramolecular assemblies sustained by two O-H···N hydrogen bonds.

Whereas

the

head-to-head

photoproduct

(rctt)-dimethyl-3,4-bis(pyridin-3-

yl)cyclobutane-1,2-dicarboxylate forms using 4,6-di-X-res (X = Cl or Br), the head-to-tail regioisomer (rctt)-dimethyl-2,4-bis(pyridin-3-yl)cyclobutane-1,3-dicarboxylate forms using 4,6di-I-res. The head-to-tail product is generated via unexpected embraced dimeric assemblies.

ACS Paragon Plus Environment


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The stereochemistry of the head-to-tail product is confirmed using single-crystal X-ray diffraction.

Introduction Small-molecule templates based on resorcinol (res) are useful to assemble unsymmetrical olefins into head-to-head geometries to photochemically generate head-to-head cyclobutanes in the solid state.1 The photodimerizations are achieved by an ability of two hydrogen-bond-donor groups to orient two hydrogen-bond-accepting olefins within a discrete supramolecular assembly2 based on a structure preorganized to give a head-to-head product. An alternative outcome is a photocycloaddition of an unsymmetrical olefin that generates a head-to-tail product. While head-to-tail photodimerizations using res templates have been discussed,3 that both headto-head and head-to-tail products can be generated using members of an isosteric family4 of res molecules would be less expected. Isosteric molecules tend to form similar crystal structures owing to the inherently-close relationship between substituents,5 which can translate into analogous solid-state reactivities.6 With this in mind, we report here the ability of three members of isosteric res templates to support both head-to-head and head-to-tail photodimerizations of (E)-methyl-3-(pyridin-4yl)prop-2-enoate (3-PAMe) in a series of co-crystals. Specifically, we show 3-PAMe to react to form (rctt)-dimethyl-3,4-bis(pyridin-3-yl)cyclobutane-1,2-dicarboxylate (3,3'-MeBPCD-hh) in (4,6-di-X-res)·2(3-PAMe) (where: X = Cl, Br) and (rctt)-dimethyl-2,4-bis(pyridin-3yl)cyclobutane-1,3-dicarboxylate

(3,3'-MeBPCD-ht)

in

(4,6-di-I-res)·2(3-PAMe).

The

generation of each photoproduct occurs regioselectively and in up to quantitative yield (Scheme 1).

Moreover, while the components in each co-crystal assemble to form discrete three-


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component assemblies with 3-PAMe arranged in a head-to-head geometry, we show the regiochemical outcome for X = I to be a consequence of an unexpected splayed conformation of the stacked olefins in the discrete hydrogen-bonded structure. The splayed stacking in (4,6-di-Ires)·2(3-PAMe) supports the three-component assemblies to self-assemble to form hitherto unseen embraced7 dimeric assemblies that mediate the formation of the head-to-tail photoproduct.8,9

Scheme 1 Experimental Co-crystal syntheses. 3-PAMe was synthesized according to a modified procedure.10 Co-crystals of (4,6-di-Cl-res)·2(3-PAMe), (4,6-di-Br-res)·2(3-PAMe), and (4,6-di-I-res)·2(3-PAMe) were each prepared by dissolving 50 mg of 3-PAMe in 5 mL of ethanol. Each resulting solution was added to a 2 mL solution of 0.5 mol equivalents of each res in ethanol. Within periods of 1 to 3 days, colorless single crystals formed. The crystals were filtered, dried, and analyzed using 1H NMR spectroscopy and single-crystal X-ray diffraction. All co-crystals were exposed to UV light from a 500 W medium-pressure mercury lamp within a photochemistry cabinet for approximately 150 h.

The progress of a photoreaction was monitored using 1H NMR



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spectroscopy. Co-crystals of the photoproduct using 4,6-di-I-res as the template formed via a recrystallization of 50 mg of photoreacted (4,6-di-I-res)·2(3-PAMe) in 5.0 mL of ethanol to afford 2(4,6-di-I-res)·2(3,3’MeBPDC-ht) after slow evaporation. X-ray crystallography. Diffraction data for (4,6-di-Cl-res)·2(3-PAMe) and (4,6-di-Br-res)·2(3PAMe) were collected at 293 K using graphite-monochromated Mo Kα1 radiation from a Rigaku SCXMini X-ray diffractometer equipped with a Rigaku Mercury 70 CCD camera. The cocrystal (4,6-di-I-res)·2(3-PAMe) was collected at 200 K, with the data being collected on a SMART X2S benchtop diffractometer equipped with an Oxford Desk Top Cooler lowtemperature apparatus. Data collection, initial indexing, frame integration, Lorentz-polarization corrections, and final cell parameter calculations were conducted using either CrystalClear11 or APEXII.12

Multi-scan absorption corrections were performed using either REQAB13 or

SADABS.14 Owing to the small size of the single crystal, 2(4,6-di-I-res)·2(3,3’MeBPDC-ht) was collected with synchrotron radiation. Intensity data were collected at 150 K on a D8 goniostat equipped with a Bruker APEXII CCD detector at Beamline 11.3.1 at the Advanced Light Source (Lawrence Berkeley National Laboratory) using synchrotron radiation tuned to λ = 0.77490 Å. Data collection frames were measured for a duration of 1-s at 0.3o intervals of ω with a maximum 2θ value of ~60o. The data frames were collected using the program APEXII and processed using the program SAINT. The data were corrected for absorption and beam corrections based on the multi-scan technique as implemented in SADABS.

The

crystallographic data were collected through the SCrALS (Service Crystallography at Advanced Light Source) program at the Advanced Light Source (ALS), Lawrence Berkeley National Laboratory. The solutions included anisotropic temperature factors of all non-hydrogen atoms. With the exclusion of the H-atoms of -OH groups which were located in the difference map and


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refined, H-atoms were introduced at calculated positions. Structural refinements were performed using SHELX-97.15 Crystallographic parameters for the co-crystals are given in Table 1.

Table 1. Crystal data for (4,6-di-X-res)·2(3-PAMe) and 2(4,6-di-I-res)·2(3,3’-MeBPDC-ht). X = Cl

X = Br

X=I

2(4,6-di-I-res)· 2(3,3’MeBPDC-ht)

984269

984268

984270

984271

C24H22Cl2N2O6

C24H22Br2N2O6

C24H22I2N2O6

C48H44I4N4O12

Formula weight

505.34

594.26

688.23

1,376.46

Temp.

293(2)

293(2)

200(2)

150(2)

Space group

P21/c

P21/c

P-1

P-1

a, Å

13.4861(13)

13.470(3)

9.3066(4)

12.0078(14)

b, Å

15.9134(16)

16.207(3)

12.4927(5)

12.0307(13)

c, Å

11.5490(12)

11.683(2)

13.0299(6)

18.775(2)

α, deg

90.00

90.00

117.0120(10)

92.569(2)

β, deg

95.483(5)

94.84(3)

102.6080(10)

104.246(2)

90.00

90.00

97.2420(10)

105.019(2)

2467.2(4)

2541.4(9)

1272.16(10)

2522.0(5)

4

4

2

2

1.360

1.553

1.797

1.813

µ, mm

0.305

3.230

2.513

2.535

Scan θ range for data collection, deg

ω scan

ω scan

ω scan

ω scan

1.98-25.35

1.97-22.38

2.32-26.34

1.92-31.17

Reflections measured Independent observed reflns.

12556

13154

27739

42543

4493

3158

5140

12286

Independent reflns. [I>2σ]

3259

2528

4679

10390

Data/restraints/parameters

4493/0/373

3158/0/320

5140/0/315

12286/4/629

Compound CCDC code Formula

γ, deg Volume, Å

3

Z 3

Density (calculated), g/cm -1

Rint Final R Indices [I>2σ] R Indices (all data) 2

0.0324

0.0391

0.0374

0.0604

R1 = 0.0426

R1 = 0.0304

R1 = 0.0205

R1 = 0.0451

wR2 = 0.1041

wR2 = 0.0687

wR2 = 0.0493

wR2 = 0.1211

R1 = 0.0673

R1 = 0.0449

R1 = 0.0231

R1 = 0.0530

wR2 = 0.1184

wR2 = 0.0743

wR2 = 0.0504

wR2 = 0.1270

1.056

1.048

1.044 1.049 Goodness-of-fit on F 2 2 2 2 2 1/2 R1 = ∑||Fo| - |Fc||/∑|Fo|, wR2 = [∑ [w(Fo -Fc ) ]/∑ [w(Fo ) ] Goodness-of-fit = [∑w(|Fo|-|Fc|)2/(Nobs-Nparameter)]1/2



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Results and Discussion Cyclobutanes functionalized with pyridyl and carboxylic acid groups are attractive building blocks in crystal engineering.16 In this context, we have shown that a combination of Ag(I)···Ag(I) forces and coordination bonds can assemble 3-PAMe in a head-to-head geometry in the solid state for a photodimerization that generates 3,3'-MeBPCD-hh stereoselectively and in quantitative yield.17 In efforts to employ small-molecule templates to direct solid-state photocycloadditions via hydrogen bonds, we turned to study the reactivity of 3-PAMe when co-crystallized with a res.18 Olefins based on 3-pyridyl groups are less explored in solid-state cycloadditions using res molecules as templates. The sole report is the use of a res to assemble trans-1-(2-pyridyl)-2-(3pyridyl)ethylene (2,3’-bpe) in a head-to-head and face-to-face stacked geometry to form head-tohead rctt-1,2-bis(2-pyridyl)-3,4-bis(4-pyridyl)cyclobutane (2,3’-tpcb).19 The photoproduct, once removed from the template, was shown to support the formation of a metal-organic polyhedron (MOP) based on a tetrahedral topology.19 In related work, 1,8-naphthalenedicarboxylic acid has directed 3,4’-bpe to undergo a head-to-head photodimerization to give 3,4’-tpcb.20

The

cyclobutane supported the formation of both a two-dimensional (2D) metal-organic framework (MOF) and metal-organic gel (MOG).20 There have been no reports on the use of a res to assemble a mono-3-pyridyl-substituted olefin for a photocycloaddition in a solid. A general underutilization of the 3-pyridyl group in coordination-driven self-assembly and metal-organic materials also motivated our studies.21 Co-crystals of (4,6-di-X-res)·2(3-PAMe) (X = Cl, Br, I) were each prepared by mixing ethanolic solutions of 3-PAMe with an appropriate res (2:1 ratio) and allowing the resulting


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solution to stand at room temperature for periods of 1 to 3 days. The formulation of each solid was confirmed using both single-crystal X-ray diffraction and 1H NMR spectroscopy. Single-crystal X-ray analyses of (4,6-di-X-res)·2(3-PAMe) (X = Cl, Br, I) reveal the components in each solid to assemble to form discrete, three-component hydrogen-bonded assemblies (Fig. 1). For X = Cl and Br (Figs. 1a,b), the solids are isostructural, crystallizing in the monoclinic space group P 21/c. For X = I (Fig. 1c), the components crystallize in the triclinic space group P ī.

(a)

(b)

(c)

15.6˚

(d)

(e)

Figure 1. X-ray structures (4,6-di-X-res)·2(3-PAMe) of three-component assemblies. Side-on views: (a) X = Cl, (b) X = Br, (c) X = I. Overhead views: (d) X = Cl and (e) X = I. Note: splayed conformation for X = I indicated.

The hydrogen-bonded assemblies in each solid (4,6-di-X-res)·2(3-PAMe) (X = Cl, Br, I) are each sustained by two O-H···N hydrogen bonds such that the carbon-carbon double (C=C) bonds are oriented into head-to-head geometries (Table 2). Each 3-pyridyl ring of 3-PAMe is



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tilted out of the plane of each res, as demonstrated by pyr···res tilt angles that range from 69.6 to 72.7o. For X = Cl and Br, the olefins are stacked in a face-to-face conformation17 (Fig. 1d) while for X = I the olefins lie severely offset (Fig. 1e). The resulting pyr···res tilt angles for X = I are, thus, accompanied by relatively large ‘splaying’ of the angle (15.6˚) subtended by the stacked olefins. The corresponding angles for X = Cl (0.68˚) and Br (0.23˚) are consistent with the faceto-face stacking conformation in each structure. As a consequence of the assembly processes, the C=C bonds for X = Cl and Br lie parallel and satisfy the distance criterion of Schmidt for a head-to-head photodimerization.22 For X = I, the C=C bonds lie beyond the criterion for a photoreaction, which can be attributed to the splayed conformation of the olefins.

Table 2. Geometries of components of discrete hydrogen-bonded assemblies. 4,6-di-X-res Cl Br I

O···N (Å) 2.717(2), 2.733(2) 2.721(2), 2.781(2) 2.706(7), 2.765(7)

C···C (Å) 4.00 4.05 5.00

pyr···res tilt (o) 69.6, 72.7 70.1, 72.2 47.8, 50.9

olefin-olefin (o) 0.68 0.23 15.6

The hydrogen-bonded assemblies (4,6-di-X-res)·2(3-PAMe) (X = Cl and Br) pack in the solid state to form side-on dimers (Fig. 2). The dimers sit around a crystallographic center of inversion, being sustained by self-complementary C-H···O forces involving each stacked olefin (C···O (Å): 3.3098(2), 3.3040(2) for Cl and 3.3573(5), 3.3712(5) for Br) (Fig. 2a). The dimers self-assemble to form a two-dimensional (2D) double-layered structure within the crystallographic bc-plane (Fig. 2b). The layers are sustained by a combination of type II X···X (X···X (Å): 3.6033(3) for Cl and 3.6894(5) for Br; ǀθ1-θ2ǀ (o): 43.0 for Cl and 48.5 for Br) and X···O forces23 [X···O (Å): 3.815(1) for Cl and 3.957(3) for Br)] involving three separate res molecules. The res molecules lie approximately perpendicular to each other within a layer. The olefins interact via edge-to-face π-forces within a layer (Fig. 2c). As a result of the assembly


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process, C=C bonds of nearest-neighbor dimeric assemblies lie outside the limit for a [2+2] photodimerization in a solid (C···C (Å): 4.99 for Cl and 5.04 for Br).

(a)

(b) ClCl interactions

OCl interactions

ClCl interactions

(c) Figure 2. X-ray structure (4,6-di-Cl-res)·2(3-PAMe): (a) side-on dimer, (b) double-layered structure, and (c) Cl···Cl and Cl···O forces (X = Cl and Br are isostructural). When (4,6-di-Cl-res)·2(3-PAMe) and (4,6-di-Br-res)·2(3-PAMe) were each exposed to UV-irradiation (medium power Hg lamp) for a period of ca 150 h, 3-PAMe reacted to form 3,3'MeBPCD-hh in up to quantitative yield (yields: 72% for X = Cl; 100% for X = Br). The formation of the head-to-head photoproduct was realized by the disappearance of the olefinic protons (6.87 and 7.77 ppm) and emergence of cyclobutane protons (4.15 and 4.37 ppm) in the



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H NMR spectrum.17 The formation of the photoproduct 3,3'-MeBPCD-hh is in line with the

head-to-head geometry adopted by the stacked olefins within each discrete hydrogen-bonded structure. Whereas side-on dimers form for X = Cl and Br, offset dimers form for X = I (Fig. 3). In the arrangement, only a single pair of olefins participates in C-H···O forces [C···O (Å): 3.357(4), 3.408(4)] within each dimeric structure (Fig. 3a). The offset stacking, in combination with the splayed conformation of 3-PAMe, means that olefins between assemblies and within a dimer, in contrast to (4,6-di-X-res)·2(3-PAMe) (X = Cl, Br), stack in a head-to-tail geometry (Fig. 3b). The head-to-tail stacking within a dimer results in two sets of C=C bonds being parallel and separated by 3.92 Å, which conforms to the geometry of Schmidt. The mode of stacking within the dimer can be likened to the three-component hydrogen-bonded assemblies adopting embraced structures.7 The dimeric assemblies pack, in contrast to X = Cl and Br, to form 1D ladder-like columns (Fig. 3c). Adjacent res molecules within each ladder participate in type II I···I forces (I···I (Å): 4.009(1); ǀθ1-θ2ǀ (°): 57.3). I···O [I···O (Å): 3.586(2)] forces that, in contrast to X = Cl and Br, are manifested in a bifurcated geometry, are present involving two res molecules. The res molecules lie parallel within the 1D extended structure. Adjacent olefins participate in face-to-face π-forces and interact via C-H···O hydrogen bonds [C···O (Å): 3.304(3)].

The larger size of the I-atom likely supports the formation of the bifurcated

interaction to result in the different mode of packing compared to X = Cl and Br.23 Indeed, effects of the larger size can be manifested sterically in terms prohibiting a form of packing compared to X = Cl and Br and electronically where both the O- and I-atoms are able to interact with the large positive region (i.e. σ-hole) of the I-atom.24 The C=C bonds of nearest-neighbor assemblies along the column are separated by 4.53 Å.


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(a)

(b)

bifurcated II/IO interactions

(c) Figure 3. Embraced dimers in (4,6-di-I-res)·2(3-PAMe): (a) stick view, (b) stick/space-filling view to highlight head-to-tail stacking, and (c) face-to-face stacking into 1D ladder columns.

When (4,6-di-I-res)·2(3-PAMe) was exposed to UV-irradiation (medium power Hg lamp) for a period of ca 150 h, 3-PAMe reacted quantitatively (yield 100% for X = I) to form a product with cyclobutane signals centered at 4.09 and 4.46 ppm. The positioning of the signals, thus, did not match (4,6-di-X-res)·2(3-PAMe) (X = Cl and Br) wherein 3-PAMe reacted to form 3,3'MeBPCD-hh.

Given the head-to-tail packing of 3-PAMe within the embraced dimeric

assemblies of (4,6-di-I-res)·2(3-PAMe), we assigned the structure of the photoproduct as 3,3'MeBPCD-ht.



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The stereochemistry of 3,3'-MeBPCD-ht was confirmed in a re-crystallization of the photoreacted solid from ethanol.

As determined by single-crystal X-ray diffraction, the

components assemble in 2(4,6-di-I-res)·2(3,3’-MeBPDC-ht), which crystallizes in the triclinic space group P ī, to form a four-component assembly sustained by four O-H···N hydrogen bonds [O···N (Å): 2.714(5), 2.716(5), 2.732(5), 2.809(4)] (Fig. 4).

The stereochemistry of the

cyclobutane ring matches the head-to-tail arrangement of the C=C bonds in (4,6-di-I-res)·2(3PAMe) (Fig. 4a). Two photoproducts are organized within each discrete assembly such that the cyclobutane rings adopt a stacked tongue-in-groove fit within the hydrogen-bonded structure. We are unaware of a case wherein multiple copies of a cyclobutane photoproduct assembles within a discrete hydrogen-bonded structure with a res.3 The assemblies pack as dimers that are sustained I···O [I···O (Å): 3.689(3)] forces (Fig 4b).

IO interactions

(a)

(b)

Figure 4. X-ray structure of 2(4,6-di-I-res)·2(3,3’-MeBPCD-ht): (a) four-component assembly and (b) localized dimer.


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Conclusion In this contribution, we have utilized an isosteric family of res based on 4,6-di-X-res to achieve regiocontrolled intermolecular [2+2] photodimerizations of 3-PAMe. Both head-to-head (X = Cl, Br) and head-to-tail (X = I) isomers of 3,3’-MeBPCD form. In addition to increasing the structural diversity of molecules generated in organic solids using co-crystals, our results shed further insight into subtle effects that crystal packing can have on chemical reactivity in the solid state, particularly in the wake of enforced assembly properties using principles of supramolecular chemistry. We are now working to incorporate both head-to-head and the headto-tail photoproducts of the 3-pyridyl group as building blocks of coordination and metal-organic materials.

Acknowledgements We are grateful to Webster University for a Faculty Research Grant and Faculty Development Fund (R.H.G) as well as the National Science Foundation (L.R.M., DMR1408834) for funding. The authors would also like to acknowledge California State University San Marcos for the funds to purchase the Rigaku SCXMini X-ray diffractometer. The ALS is supported by the U.S. Department of Energy, Office of Energy Sciences Materials Sciences Division, under contract DE-AC02-05CH11231.

References 1. MacGillivray, L. R.; Papaefstathiou, G. S.; Friščićc, T.; Hamilton, T. D.; Bučar, D. -K.; Chu, Q.; Varshney, D. B.; Georgiev, I. G. Acc. Chem. Res. 2008, 41, 280.



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2. (a) Kole, G. K.; Vittal, J. J. Chem. Soc. Rev. 2013, 42, 1755. (b) Bhogala, B. R.; Burjor, C.; Parthasarathy, A.; Ramamurthy, V. J. Am. Chem. Soc. 2010, 132, 13434. (c) Ramkinkar, S.; Biradha, K. CrystEngComm. 2011, 13, 3246. 3. MacGillivray, L. R.; Reid, J. L.; Ripmeester, J. A. J. Am. Chem. Soc. 2000, 122, 7817. 4. Isosterism is the replacement of one functional group in a molecule by another of ‘similar’ electronic structure, see: Sein Jr., L. T.; Wie, Y.; Jansen, S. A. J. Phys. Chem. A 2000, 104, 11371. 5. For considerations on isosteric groups in the solid state, see: Dikundwar, A. G.; Pete, U. D.; Zade, C. M.; Bendre, R. S.; Row, T. N. G. Cryst. Growth Des. 2012, 12, 4530. 6. Bučar, D.-K.; Sen, A.; Mariappan, S.V.S.; MacGillivray, L.R. Chem. Commun. 2012, 48, 1790. 7. (a) Zareba, J.; Bialek, M. J.; Janczak, J.; Zon, J.; Dobosz, A. Cryst. Growth Des. 2014, 14, 6143. (b) Arman, H. D.; Rafferty, E. R.; Bayse, C. A.; Pennington, W. T. Cryst. Growth Des. 2012, 12, 4315. (c) Dance, I.; Scudder, M. CrystEngComm 2009, 11, 2233. 8. For studies on anion control of regiochemistry of the [2+2] photodimerization in solids, see: (a) Kole, G. K.; Tan, G. K.; Vittal, J. J. CrystEngComm 2012, 14, 7438; (b) Kole, G. K.; Tan, G. K.; Vittal, J. J. J. Org. Chem. 2011, 76, 7860; (c) Kole, G. K.; Tan, G. K.; Vittal, J. J. Org. Lett. 2010, 12, 128. 9. For studies on Ag(I) ions to promote [2+2] photodimerizations of unsymmetrical olefins in solids, see: (a) Laird, R. C.; Sinnwell, M. A.; Nguyen, N. P.; Swenson, D. C.; Mariappan, S. V. S.; MacGillivray, L. R. Org. Lett. 2015, 17, 3233; (b) Samai, S.; Ghosh,


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23. (a) Mukherjee, A.; Tothadi, S.; Desiraju, G. R. Acc. Chem. Res. 2014, 47, 2514; (b) Pigge, F. C.; Vangala, V. R.; Swenson, D. C.; Rath, N. P. Cryst. Growth Des. 2010, 10, 224. 24. (a) Hatwar, V. R.; Row, T. N. G. J. Phys. Chem. A 2010, 114, 13434; (b) Lo, R.; Ballabh, A.; Singh, A.; Dastidar, P.; Ganguly, B. CrystEngComm 2012, 14, 1833.


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Regiocontrol of the [2+2] Photodimerization in the Solid State using Isosteric Resorcinols: Head-to-Tail Cyclobutane Formation via Unexpected Embraced Assemblies

Devin P. Ericson,a Zachary P. Zurfluh-Cunningham,a Ryan H. Groeneman,a* Elizabeth Elacqua,b Eric W. Reinheimer,c Bruce C. Noll,d and Leonard R. MacGillivrayb* a. Department of Biological Sciences, Webster University, St. Louis, MO 63119 b. Department of Chemistry, University of Iowa, Iowa City, IA 52242 c. Department of Chemistry and Biochemistry, W.M. Keck Foundation Center for Molecular Structure, California State University San Marcos, San Marcos, CA 92096 d. Bruker AXS Inc., 5465 East Cheryl Parkway, Madison, WI 53711 Email: [email protected], Tel: +1 314-246-7466 Email: [email protected], Fax: +1 319-335-1270; Tel: +1 319-335-3504

For Table of Contents Use Only

side-on dimer

embraced dimer

Regiocontrolled head-to-head and head-to-tail [2+2] photodimerizations are achieved in the solid state using isosteric templates based on resorcinol.


Regiocontrol of the [2 + 2] Photodimerization in the Solid State Using

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