Oxa-Pictet–Spengler reaction as key step in the synthesis of novel σ receptor ligands with 2-benzopyran structure

Article abstract of DOI:10.1016/j.bmc.2016.06.046

The Oxa-Pictet–Spengler reaction of methyl 3-hydroxy-4-phenylbutanoate (8) was explored to obtain novel σ receptor ligands. 1-Acyl protected piperidone ketals 10 and 11 reacted with phenylethanol 8 to yield spirocyclic compounds. Aliphatic aldehyde acetals 19 provided 1,3-disubstituted 2-benzopyrans 20 with high cis-diastereoselectivity. The intramolecular Oxa-Pictet–Spengler reaction of 24 led to the tricyclic compound 25. The spirocyclic compounds 18 show high σ₁affinity (K_i20–26?nM) and σ₁/σ₂selectivity (>9-fold), when a large substituent (n-octyl, benzyl, phenylpropyl) is attached to the piperidine N-atom. Opening of the piperidine ring to yield aminoethyl (22, 23) or aminomethyl derivatives (21) resulted in reduced σ₁affinity and σ₁/σ₂selectivity.

Full text of DOI:10.1016/j.bmc.2016.06.046

Accepted Manuscript
Oxa-Pictet-Spengler reaction as key step in the synthesis of novel σ receptor
ligands with 2benzopyran structure
Inga Knappmann, Dirk Schepmann, Bernhard Wünsch
PII:
S0968-0896(16)30469-2
DOI:
http://dx.doi.org/10.1016/j.bmc.2016.06.046
BMC 13102
Reference:
Bioorganic & Medicinal Chemistry
To appear in:
Received Date:
Revised Date:
Accepted Date:
18 April 2016
17 June 2016
23 June 2016
Please cite this article as: Knappmann, I., Schepmann, D., Wünsch, B., Oxa-Pictet-Spengler reaction as key step in
the synthesis of novel σ receptor ligands with 2benzopyran structure, Bioorganic & Medicinal Chemistry (2016),
doi: http://dx.doi.org/10.1016/j.bmc.2016.06.046
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Oxa-Pictet-Spengler reaction as key step in the synthesis of novel  receptor
ligands with 2-benzopyran structure
Inga Knappmann,a Dirk Schepmann,a Bernhard Wünsch*a,b
a
Institut für Pharmazeutische und Medizinische Chemie der Universität Münster,
Corrensstraße 48, D-48149 Münster, Germany
Tel.: +49-251-8333311; Fax: +49-251-8332144; E-mail: wuensch@uni-muenster.de
b Cells-in-Motion Cluster of Excellence ((EXC 1003 – CiM), Westfälische Wilhelms-
Universität Münster, Germany
Abstract
The Oxa-Pictet-Spengler reaction of methyl 3-hydroxy-4-phenylbutanoate (8) was
explored to obtain novel  receptor ligands. 1-Acyl protected piperidone ketals 10
and 11 reacted with phenylethanol 8 to yield spirocyclic compounds. Aliphatic
aldehyde acetals 19 provided 1,3-disubstituted 2-benzopyrans 20 with high cis-
diastereoselectivity. The intramolecular Oxa-Pictet-Spengler reaction of 24 led to the
tricyclic compound 25. The spirocyclic compounds 18 show high 1 affinity (Ki 20-26
nM) and 1/2 selectivity (>9-fold), when a large substituent (n-octyl, benzyl,
phenylpropyl) is attached to the piperidine N-atom. Opening of the piperidine ring to
yield aminoethyl (22, 23) or aminomethyl derivatives (21) resulted in reduced 1
affinity and 1/2 selectivity.
1

Key words:  ligands; Oxa-Pictet-Spengler reaction; intramolecular Oxa-Pictet-
Spengler reaction; 2-benzopyrans; spirocyclic piperidines; tricyclic systems; aryl-N-
distance
1. Introduction
At first, the nature of the receptor was controversially discussed: originally it was
regarded as opioid receptor subtype, then as binding site at the NMDA receptor and
now it is accepted as unique receptor type without relationship to any other
mammalian protein. There exist two subtypes termed 1 and 2 receptors, which
differ in their molecular weight, tissue distribution and ligand binding profile.1-5
The 1 receptor is involved in various neurological disorders, including depression
and anxiety, cognitive deficits, psychosis, pain and dependence (cocaine, ethanol).6-8
The importance of 1 receptors is emphasized by the fact that several antipsychotics
(e.g. haloperidol),9 antidepressants (e.g. opipramol, fluvoxamine)10 and anti-
Alzheimer drugs (e.g. donepezil)11 show in addition to their main activity interactions
with 1 receptors. Additionally, 1 ligands are able to modulate the analgesic activity
of opioid analgesics. The 1 agonist (+)-pentazocine antagonized the analgesic
effects of morphine, whereas the 1 antagonist haloperidol reversed this effect and
moreover led to potentiation of morphine analgesia.12 The particular role of 1
receptors in the field of neuropathic pain was shown with 1 receptor knock-out
mice.13 The pyrazole derivative S1RA is currently under clinical investigation for the
therapy of neuropathic pain.14 A significantly increased level of 1 receptors was
found in some human tumor cell lines including brain, breast, lung and prostate
2

cancer cell lines. Since 1 receptor antagonists were shown to induce apoptosis in
human tumor cell lines, selective targeting of σ1 receptors represents a promising
strategy for the development of a novel antitumor therapy.15-18
In addition to overexpression of σ1 receptors, σ2 receptors are also upregulated in
various human tumor cell lines. It was shown that apoptotic processes could be
induced by activation of σ2 receptors highly expressed in rapidly proliferating tumor
cells.18-20
During the past decades, substantial efforts have been spent on the generation of
novel 1 and 2 receptor ligands. Based on pharmacophore models21 and a 3D-
homology model22 of the 1 receptor, we have developed spirocyclic compounds
showing high 1 receptor affinity. Both the benzofuran and benzopyran derivatives 1a
(Ki = 1.1 nM) and 1b (Ki = 1.3. nM) display very high 1 receptor affinity and more
than 1000-fold selectivity over the 2 subtype. (Figure 1) In the capsaicin assay, an
animal model for neuropathic pain, the benzofuran 1a sowed promising analgesic
activity.23-25 Starting with the high 1 affinity and selectivity of 1a a series of
homologous fluoroalkyl derivatives was designed as PET (positron emission
tomography) tracers26-31 resulting in the fluoroethyl derivative fluspidine (2). [18F]-
labeled (S)-configured fluspidine [18F]-(S)-2 is currently under clinical investigation as
PET tracer for imaging of 1 receptors in the central nervous system.28 Spirocyclic
compounds with differently annulated thiophene rings (e.g. 3) were prepared
revealing high 1 affinity. Depending on the position of the phenyl moiety introduced
at the very end of the synthesis, thiophenes 3 and regioisomers show reverse binding
modes in the 1 receptor binding pocket.32
3

In the mouse acetic acid writhing assay the 1,6-epoxy-3-benzazonine 4 showed
analgesic activity with an ED50 value of 20 mg /kg body weight.33 (Figure 1) Both the
spirocyclic 1 ligands 1b and 3 and the epoxy-3-benzazonine 4 contain the
benzopyran substructure. In both types of ligands the arylalkylamine pharmacophore
is conformationally restricted: in 1-3 it is embedded in a spirocyclic system and in 4 in
a tricyclic system. However, the distance between the benzene ring and the basic
amino moiety is different in the spirocyclic compounds 1-3 compared to the tricyclic
compound 4.
Figure 1: Benzofuran and benzopyran based 1 ligands and analgesics with
conformationally restricted arylalkylamine substructure.
The Oxa-Pictet-Spengler reaction is the condensation of a 2-arylethanol derivative
with an aldehyde, ketone or derivatives thereof to produce 3,4-dihydro-2-1H-
benzopyrans.34-36 This oxygen variation of the Pictet-Spengler reaction is a versatile
method to synthesize variously substituted 2-benzopyrans and larger fused ring
systems. Moreover, intramolecular versions are known.37 It is promoted by Broensted
.
or Lewis acids, including BF3 OEt2, TMSOTf, and Bi(OTf)3,38 and can be applied for
the stereoselective synthesis of complex natural products.39-41
4

In order to broaden the relationships between the structure of 1-aminoalkyl
substituted 2-benzopyrans and their 1 affinity and selectivity over the 2 subtype,
modifications of the side chain in 3-position and the aminoalkyl part of the
compounds were envisaged. In order to get access to a side chain bearing an
appropriate substituent, the Oxa-Pictet-Spengler reaction using 3-hydroxy-4-
phenylbutanoate 8 as 2-phenylethanol component should be applied. Herein, the
applicability of the -hydroxyester 8 as arylethanol component in the inter- and
intramolecular Oxa-Pictet-Spengler reaction should be investigated. Moreover, its
reaction with various carbonyl compounds should lead to 2-benzopyrans with
conformationally restricted or flexible phenylalkylamine substructures. The selection
of the substituents at the 2-benzoparyn system was driven by the substitution pattern
of known  lead compounds as shown in Figure 1.
2. Synthesis
The -hydroxyester 842,43 was the central building block of this project. It was
prepared by NaBH4 reduction of the -ketoester 7, which was obtained in a two-step,
one-pot synthesis. At first, Meldrum’s acid (6) was acylated with phenylacetyl chloride
in the presence of pyridine. The product was then heated in methanol resulting in
decomposition of the triacyl intermediate into an acylketene, which reacted with
methanol to afford the -ketoester 7.44 The -hydroxyester 8 was obtained in 59 %
yield over two steps from phenylacetyl chloride. (Scheme 1)
5

Scheme 1: Synthesis of -hydroxyester 8.
Reagents and reaction conditions: (a) 1. Pyridine, CH2Cl2, 2.5 h; 2. CH3OH, reflux, 2
h, 72 %. (b) CH3OH, NaBH4, rt, 20 h, 82 %.
In order to synthesize spirocyclic benzopyran derivatives with a piperidine ring, 1-
benzylpiperidin-4-one and its dimethyl ketal 9 were employed in the Oxa-Pictet-
Spengler reaction with -hydroxyester 8. However, all attempts failed to give the
corresponding spirocyclic benzopyrans. It was assumed that the basic piperidine ring
reacted first with the added Broensted or Lewis acid, thus inhibiting the acid induced
formation of a cation in 4-position of the piperidine ring.
Therefore, non-basic 1-acyl protected piperidin-4-ones were employed in the Oxa-
Pictet-Spengler reaction. Since these piperidin-4-ones did not react with the -
hydroxyester 8, the ketals 10 and 11 were prepared by ketalization of the
corresponding ketones with methanol and trimethyl orthoformate. In the presence of
.
BF3 OEt2 the -hydroxyester 8 reacted with the ketals 10 and 11 to afford the
spirocyclic benzopyrans 12 and 13 in 86 % and 22 % yield, respectively.
6

Scheme 2: Synthesis of 2-benzopyrans with spirocyclic connected piperidine ring.
.
Reagents and reaction conditions: (a) BF3 OEt2, toluene, rt, 6 h, 86 % (12), or 8 d, 22
% (13). (b) LiBH4, THF, rt, 20 h, 76 %. (c) H2 (balloon), Pd/C, CH3OH, rt, 20 h, 89 %.
(d) NaOH, reflux, 3 h, 53 %. (e) BrCH2CH2CH2Ph, CH3CN, K2CO3, reflux, 4 h, 69 %.
(f) R-Br, CH3CN, reflux, 4 h, 42-70 % (18a-c, 18e); reflux, 20 h for Bn-Br, 17 % (18d).
The compounds 8 and 12-18 were prepared as racemic mixtures.
The ester in the side chain of the N-acetyl derivative 12 was reduced with LiBH4 to
provide the primary alcohol 15 in 76 % yield. The Cbz- and Ac-protective groups of
the ester 13 and the alcohol 15 were cleaved off hydrogenolytically and upon
treatment with NaOH, respectively. The resulting secondary amines 14 and 16 were
alkylated with various alkyl bromides in the presence of K2CO3 to obtain the N-
substituted spirocyclic piperidine derivatives 17e and 18a-e. Since the Oxa-Pictet-
Spengler reaction with the Cbz-protected ketal 11 provided spirocyclic 2-benzopyran
13 in only 22 % yield, only the phenylpropyl derivative 17e with an ester side chin
was prepared.
7

Scheme 3: Synthesis of 1-(aminoalkyl) substituted 2-benzopyrans.
.
Reagents and reaction conditions: (a) BF3 OEt2, toluene, CH2Cl2, rt, 2-4 d, 84-99 %
(20a,c,d), 32 % (20b). (b) 20a, piperidine or 4-phenylpiperidine, Bu4NI, K2CO3,
CH3CN, reflux, 20 h, 16 % (21b), 11 % (21c). (c) 20b, pyrrolidine, piperidine, or 4-
phenylpiperidine, Bu4NI, K2CO3, CH3CN, reflux, 20 h, 38-64 %. (d) LiBH4, THF, rt, 20
h, 43 % (23b). (e) LiAlH4, THF, 0 °C, 2 h, 66 % (23c). (f) NaN3, DMF, 60-70 °C, 24 h,
28 %. (g) H2, Pd/C, CH3OH. Only one enantiomer of the racemic mixtures is shown,
respectively.
The synthesis of analogs of 17 and 18 with linear substituents in 1-position of the 2-
benzopyran ring was envisaged by reaction of -hydroxyester 8 with aliphatic
aldehyde acetals. In particular acetals with additional substituents in the side chain
were considered, which should allow the introduction of basic amino moieties. For
this purpose bromoacetaldehyde acetal 19a and chloropropionaldehyde acetal 19b
.
were reacted with the -hydroxyester 8 in the presence of BF3 OEt2. The
bromomethyl derivative 20a was obtained in 86 % yield, whereas the chloroethyl
8

derivative 20b was isolated in only 32 % yield. The lower yield of the chloroethyl
derivative 20b might be explained by fast -elimination. Although a second center of
chirality in 1-position was established, only one diastereomer of the haloalkyl
substituted 2-benzopyrans 20a and 20b was isolated after Oxa-Pictet-Spengler
reaction. The relative configuration of the haloalkyl derivatives 20a and 20b was
determined by nuclear Overhauser effect (NOE) experiments. For example for 20a,
irradiation with the resonance frequency of 3-H at 4.18 ppm resulted in an increased
signal at 5.09 ppm (1-H) indicating the cis-orientation of these protons. Obviously,
during the Oxa-Pictet-Spengler reaction thermodynamically more stable cis-
configured diastereomers were formed with high diastereoselectivity.
Nucleophilic substitution of the bromomethyl and chloroethyl derivatives 20a and 20b
with secondary amines (pyrrolidine, piperidine, 4-phenylpiperidine) led to the tertiary
amines 21b,c and 22a-c. In order to increase the yields and the reaction rate,
tetrabutylammonium iodide was added to the reaction mixture. The primary alcohols
23b and 23c were obtained by LiBH4 and LiAlH4 reduction of the esters 22b and 22c,
respectively. The 1 and 2 affinities of the spirocyclic amines 17 and 18 as well as
the tertiary amines 21-23 were tested in receptor binding studies.
The substituent in 1-position of the 2-benzopyran ring should be used to form tricyclic
systems by connecting it with the ester group in 3-position of cis-configured 2-
benzopyrans 20. Subsequently, a basic functional group should be installed at or
within the newly formed bridge. At first a Dieckmann condensation of diesters 20c
and 20d was envisaged, which were prepared by Oxa-Pictet-Spengler reaction of -
.
hydroxyester 8 with acetals 19c and 19d and BF3 OEt2. Only one diastereomer of
20c and 20d was found indicating high diastereoselectivity of the Oxa-Pictet-
9

Spengler reaction. A positive NOE between the protons in 1-ppsition (5.23 ppm) and
3-position (4.14 ppm) confirmed the thermodynamically favored cis-configuration of
20d and indirectly of 20c as well.
Although the Dieckmann cyclization of diesters 20c and 20d was tried with different
bases (NaH/CH3OH, NaH/EtOH, NaOCH3/CH3OH, KOtBu, LHMDS; LDA) in different
solvents under different reaction conditions, tricyclic systems could not be identified.
Usually the starting diesters 20c and 20d were re-isolated, although cis/trans-
isomerization with strong bases and transesterification with alcohols were observed.
According to the next idea, the bromomethyl derivative 20a was transformed into the
azidomethyl derivative 20e. Reduction of the azide 20e with H2 and Pd/C led to the
primary amine 20f, which upon treatment with Lewis or Broensted acids did not react
with the ester in 3-position to yield the lactam 25.
Therefore, the strategy was changed into an intramolecular Oxa-Pictet-Spengler
reaction. Aminolysis of the -hydroxyester 8 with aminoacetaldehyde dimethyl acetal
led to the amide 24 containing both the phenylethanol and acetal structural elements.
.
The intramolecular Oxa-Pictet-Spengler reaction of 24 was catalyzed by BF3 OEt2
affording the tricyclic lactam 25. Several optimization experiments were performed,
but the yield of the tricyclic lactam 25 did not exceed 10 %. The lactam 25 had been
previously prepared by a Schmidt rearrangement of 1,4,5,6-tetrahydro-1,5-
epoxybenzo[8]annulen-3(2H)-one. Whereas Schmidt rearrangement provided two
regioisomers,33 the intramolecular Oxa-Pictet-Spengler reaction yielded only one
regioisomer, although in low yields. The transformation of the lactam 25 into the
10

analgesically active amine 4 required LiAlH4 reduction and methylation as reported in
literature.33
Scheme 4: Synthesis of tricyclic benzopyrans by intramolecular Oxy-Pictet-Spengler
reaction.
Reagents and reaction conditions: (a) H2NCH2CH(OCH3)2, pTosOH, reflux, 69 %. (b)
.
toluene, CH2Cl2, rt, 30 min, then addition of BF3 OEt2 40-50 °C, 2 d, 10 %. (c) two
steps according to ref.33. The compounds 24, 25 and 4 were prepared as racemic
mixtures.
3. Receptor affinity
The 1 affinity of the 2-benzopyrans was tested in radioligand receptor binding
studies with guinea pig brain membrane preparations and the radioligand [3H]-(+)-
pentazocine. In the 2 assay rat liver membrane preparations and [3H]di-o-
tolylguanidine were used. Since di-o-tolylguanidine also interacts with 1 receptors,
an excess of (+)-pentazocine was added to mask the 1 receptors.45-47 The affinity
data of the tested 2-benzopyrans are summarized in Table 1.
11

Table 1: Affinity of 2-benzopyrans towards 1 and 2 receptors.
Ki ± SEM (nM) (n = 3)[a]
σ1/σ2
compd.
R1 or NR2
R2
selectivity
1
2
17e
18a
18b
18c
18d
18e
21b
21c
22a
22b
22c
23b
23c
Ph(CH2)3
Et
CO2CH3
CH2OH
CH2OH
CH2OH
CH2OH
CH2OH
CO2CH3
CO2CH3
CO2CH3
CO2CH3
CO2CH3
CH2OH
CH2OH
39 ± 5.0
0 %*
610 ± 230
0 %*
15
--
n-Bu
60 ± 13
26 ± 8
13 %*
--
n-Oct
234 ± 28
0 %*
9
PhCH2
20 ± 6
--
Ph(CH2)3
20 ± 2
617 ± 73
7 %*
30
--
Piperidin-1-yl
4-Ph-piperidin-1-yl
Pyrrolidin-1-yl
Piperidin-1-yl
4-Ph-piperidin-1-yl
Piperidin-1-yl
4-Ph-piperidin-1-yl
510 ± 100
673 ± 84
>1000
785 ± 65
0 %*
1.2
--
519 ± 64
38 ± 4.0
4 %*
0 %*
--
107 ± 50
14 %*
2.8
--
52 ± 19
2.2 ± 0.7
1.9 ± 0.2
177 ± 4
20 ± 2.0
-
0.4
(+)-Pentazocine
Haloperidol
78.1 ± 1.3
20.2 ± 1.3
Di-o-tolylguanidine
[a]
All Ki-values were recorded three times, the number of independent
experiments is 3.
12

* For low-affinity compounds only the inhibition of the radioligand binding (in %) at
a test compound concentration of 1 µM is given.
The 1 affinity of the conformationally restricted spirocyclic alcohols 18 increased with
increasing size of the N-substituent. The highest 1 affinity was found for the n-octyl
(18c, Ki = 26 nM), benzyl (18d, Ki = 20 nM) and phenylpropyl derivative (18e, Ki = 20
nM). An ester moiety in the side chain in 3-position of the 2-benzopyran (17e) slightly
reduced the 1 affinity compared to the primary alcohol 18e. 2-Benzopyrans 22 and
23 with a flexible aminoethyl side chain in 1-position, but the same aryl-N-distance
revealed slightly reduced 1 affinity compared to the more rigid spirocyclic
compounds 18. The Ki values of 22c and 23c with the large 4-phenylpiperidin-1-yl
moiety are 38 nM and 52 nM, respectively. In this case ester and alcohol in the side
chain led to almost the same 1 affinity. The smaller piperidin-1-yl moiety at the end
of the 1-ethyl spacer (22b, 23b) and shorter aminomethyl derivatives 21 resulted in
more than 10-fold reduced 1 affinity.
The highest 2 affinity in the group of spirocyclic 2-benzopyrans was found for 18c
with the large n-octyl moiety at the N-atom (Ki = 234 nM). Nevertheless, 18c showed
still a 9-fold preference for the 1 over the 2 receptor. In the class of aminoalkyl
substituted 2-benzopyrans only 4-phenylpiperidin-1-yl derivatives (c-series) revealed
considerable 2 affinity. Whereas the aminomethyl derivative 21c interacted equally
with both  receptor subtypes, the aminoethyl homolog 22c showed a slight
preference for the 1 receptor. However, the selectivity was reversed for the alcohol
23c displaying a 2.5-fold preference for the 2 subtype.
13

4. Conclusion
The Oxa-Pictet-Spengler reaction was used to synthesize a diverse set of
benzopyrans with the aim to address  receptors. Variations of the structure and
length of the aminoalkyl substituent in 1-position, the N-substituent(s) and the group
in 3-position of the 2-benzopyran ring were performed. It was found that spirocyclic
compounds 18 show high 1 affinity (Ki = 20-26 nM) and 1/2 selectivity (>9-fold),
when large substituents are attached to the N-atom. A higher flexibility of the 1-
substituent was realized with aminoethyl derivatives 22 and 23 resulting in slightly
reduced 1 affinity. Shortening of the 2-benzopyran-N-distance to three bond
lenghths as in 21 led to considerable reduction of 1 affinity. On the other hand more
flexible side chains allowed better interactions with 2 receptors leading to reduced
1/2 selectivity.
With respect to 1 affinity and 1/2 selectivity the benzyl derivative 18d (Ki(1) = 20
nM, (Ki(2) > 1 µM) represents one of the most promising 1 ligands of this series.
Compared to related spirocyclic piperidines 1-3 its 1 affinity is 10-15-fold reduced. It
is assumed that the reduced affinity is due to the 2-hydroxyethyl moiety in 3-position
of the benzopyran system, but it remains to be elucidated, whether size and/or
polarity of this moiety are responsible for this effect. However, due to the synthetic
novel strategy of the Oxa-Pictet-Spengler reaction versatile substituents can be
introduced in 3-position by starting with appropriate phenylethanol derivatives or
modification of the existing acetate or ethanol side chain.
14

5. Experimental
5.1. Chemistry, general methods
Unless otherwise noted, moisture sensitive reactions were conducted under dry
nitrogen. THF was dried with sodium/benzophenone and was freshly distilled before
use. Thin layer chromatography (tlc): Silica gel 60 F254 plates (Merck). Flash
chromatography (fc): Silica gel 60, 40–64 µm (Merck); parentheses include: diameter
of the column, eluent, fraction size, Rf value. Melting point: Melting point apparatus
SMP 3 (Stuart Scientific), uncorrected. MS: MAT GCQ (Thermo-Finnigan); IR: IR
1
13
spectrophotometer 480Plus FT-ATR-IR (Jasco). H NMR (400 MHz), C NMR (100
MHz): Unity Mercury Plus 400 spectrometer (Varian);  in ppm related to
tetramethylsilane; coupling constants are given with 0.5 Hz resolution. HPLC method
for the determination of the purity: Merck Hitachi Equipment; UV detector: L-7400;
autosampler:L-7200; pump: L-7100; degasser: L-7614; column: LiChrospher® 60 RP-
select B (5 µm), 250-4 mm; flow rate: 1.00 mL/min; injection volume: 5.0 µL;
detection at λ = 210 nm; solvents: A: water with 0.05% (v/v) CF3CO2H; B: CH3CN
with 0.05% (v/v) CF3CO2H: gradient elution: (A %): 0-4 min: 90 % , 4-29 min: gradient
from 90 % to 0 %, 29-31 min: 0 %, 31-31.5 min: gradient from 0 % to 90 %, 31.5-40
min: 90 %.
5.2. Synthetic procedures
5.2.1. Methyl 3-oxo-4-phenylbutanoate (7)44
Under N2 atmosphere, pyridine (4 g) was added over 15 min. at 0 °C to a solution of
Meldrum's acid (6, 2.88 g, 20 mmol) in CH2Cl2 (10 mL). A solution of phenylacetyl
chloride (5, 3.1 g, 20 mmol) in CH2Cl2 (8 mL) was added dropwise at 0 °C during 2 h.
After stirring for 90 min at 0 °C and 60 min at rt, CH2Cl2 (5 mL) and 2 M HCl (14 mL)
were added. The organic layer was separated and the aqueous layer was extracted
15

with CH2Cl2 (3×10 mL). The organic layer was dried (Na2SO4) and concentrated in
vacuo. The obtained orange crystals were suspended in methanol (20 mL) and the
mixture was heated to reflux for 3 h. Then the mixture was concentrated in vacuo and
the residue was purified by fc (6 cm, cyclohexane : EtOAc = 9 : 1, 30 mL, Rf = 0.41).
Colorless oil, yield 2.75 g (72 %). C11H12O3 (192.2). MS (EI): m/z = 192 [M], 91
[PhCH2]. IR:  [cm-1] = 2953 (C-H), 1745 (C=O, ester), 1715 (C=O, ketone), 729, 698
1
(C-H). H NMR (CDCl3): δ [ppm] = 3.46 (s, 2H, CH2CO2CH3), 3.71 (s, 3H, CO2CH3),
3.82 (s, 2H, PhCH2), 7.18-7.38 (m, 5H, arom.).
5.2.2. Methyl (±)-3-hydroxy-4-phenylbutanoate (8)42,43
The -ketoester 7 (2.75 g, 14.3 mmol) was dissolved in methanol (25 mL). NaBH4
(543 mg, 14.3 mmol) was added under cooling and the mixture was stirred for 20 h at
rt. Subsequently the solvent was removed in vacuo, the residue was dissolved in
water (10 mL) and acidified with 2 M HCl. The aqueous layer was extracted with Et2O
(4×20 mL), the combined organic layers were dried (Na2SO4) and concentrated in
vacuo. The residue was purified by fc (6 cm, cyclohexane : EtOAc = 4 :1, 30 mL, Rf =
0.29). Colorless oil, yield 2.29 g (82 %). C11H14O3 (194.2). MS (EI): m/z = 194 [M], 91
1
[PhCH2]. IR:  [cm-1] = 3457 (O-H), 2952 (C-H), 1730 (C=O), 699 (C-H). H NMR
(CDCl3): δ [ppm] = 2.46 (dd, J = 16.4/8.6 Hz, 1H, CH2CO2CH3), 2.52 (dd, J =
16.4/3.7 Hz, 1H, CH2CO2CH3), 2.77 (dd, J = 13.6/6.1 Hz, 1H, PhCH2), 2.87 (dd, J =
13.6/7.1 Hz, 1H, PhCH2), 3.69 (s, 3H, CO2CH3), 4.25 - 4.29 (m, 1H, CHOH), 7.20-
7.33 (m, 5H, arom.). A signal for the OH proton is not seen.
5.2.3. 1-Acetylpiperidin-4-one dimethyl acetal (10)
A solution of 1-acetylpiperidin-4-one (2.82 g, 20 mmol), trimethyl orthoformate (10.6
g) and p-toluenesulfonic acid (190 mg, 1 mmol) in CH3OH abs. (4 mL) was stirred at
16

rt for 16 h. Then 10 % NaHCO3 solution (40 mL) was added and the mixture was
extracted with CH2Cl2 (3 x 25 mL). The combined organic layers were dried (K2CO3),
concentrated in vacuo and the residue was used for the next reaction step without
further purification. Colorless oil, yield 3.26 g (87 %). C9H17NO3 (187.2). MS (EI): m/z
= 187 [M], 144 [M-COCH3]. IR:  [cm-1] = 2959 (C-H), 1640 (C=O), 1108, 1046 (C-O).
1H NMR (CDCl3): δ [ppm] = 1.44 – 1.52 (m, 4H, N(CH2CH2)2), 2.20 (s, 3H, NCOCH3),
3.49 (s, 6H, 2 x OCH3), 3.74 – 3.90 (m, 4H, N(CH2CH2)2).
5.2.4. Benzyl 4,4-dimethoxypiperidine-1-carboxylate (11)
A solution of benzyl 4-oxopiperidine-1-carboxylate (2.33 g, 8.9 mmol), trimethyl
orthoformate (5.5 mL) and p-toluenesulfonic acid (95 mg, 0.5 mmol) in CH3OH abs.
(4 mL) was stirred at rt for 2 d. Then10 % NaHCO3 solution (30 mL) was added and
the mixture was extracted with CH2Cl2 (3×15 mL). The combined organic layers were
dried (K2CO3), concentrated in vacuo and the residue was used without further
purification. Yellow oil, yield 2.85 g (> 100 %, unpurified), Rf = 0.2 (cyclohexane :
EtOAc = 4 : 1). C15H21NO4 (279.3). MS (EI): m/z = 172 [M-PhCH2O], 156 [M-Bn-
OCH3]. IR:  [cm-1] = 2960, 2830 (C-H), 1697 (C=O), 1230 (O-CH3). 1H NMR (CDCl3):
δ [ppm] = 1.68 - 1.76 (m, 4H, N(CH2CH2)2), 3.18 (s, 6H, 2 x OCH3), 3.50 (t, J = 5.7
Hz, 4H, N(CH2CH2)2), 5.12 (s, 2H, OCH2Ph), 7.28-7.33 (m, 5H, arom.).
5.2.5. Methyl (±)-2-(1'-acetyl-3,4-dihydrospiro[[2]benzopyran-1,4'-piperidin]-3-
yl)acetate (12)
Under N2, a solution of dimethyl ketal 10 (1.83 g, 9.8 mmol in toluene (2 mL) was
added to a solution of 8 (438 mg, 2.2 mmol) in CH2Cl2 (7 mL) and the mixture was
.
stirred for 30 min at rt. Then, the solution was cooled to 0 °C, BF3 Et2O (2.6 mL,
approx. 16 mmol) was added and the mixture was stirred for 6 d at rt. A 10 % solution
17

of NaHCO3 (20 mL) was added, the organic layer was separated and the aqueous
layer was extracted with CH2Cl2 (4×16 mL). The combined organic layers were dried
(Na2SO4), concentrated in vacuo and the residue was purified by fc (4 cm,
cyclohexane : EtOAc = 1 : 1, 20 mL, Rf = 0.18). Pale yellow oil, yield 602 mg (86 %).
C18H23NO4 (317.4). MS (EI): m/z = 317 [M], 274 [M-COCH3]. IR:  [cm-1] = 2925 (C-
1
H), 1736 (C=O ester), 1634 (C=O amide). H NMR (CDCl3): δ [ppm] = 1.64 – 1.75
(m, 2H, N(CH2CH2)2), 1.99 (td, J = 13.2/4.9 Hz, 1H, N(CH2CH2)2), 2.13 (s, 3H,
NCOCH3), 2.09 – 2.20 (m, 1H, N(CH2CH2)2), 2.59 – 3.00 (m, 5H, CH2CO2CH3 (2H),
ArCH2 (2H), N(CH2CH2)2 (1H)), 3.40 – 3.56 (m, 1H, N(CH2CH2)2), 3.59 – 3.68 (m, 1H,
N(CH2CH2)2), 3.73 (s, 3H, CO2CH3), 4.20 – 4.31 (m, 1H, ArCH2CH), 4.50 – 4.58 (m,
1H, N(CH2CH2)2), 7.03 – 7.09 (m, 2H, arom.), 7.14 – 7.21 (m, 2H, arom.).
5.2.6. Methyl (±)-2-(1'-benzyloxycarbonyl-3,4-dihydrospiro[[2]benzopyran-1,4'-
piperidin]-3-yl)acetate (13)
Under N2, a solution of dimethyl ketal 11 (1.40 g, 5.0 mmol) in toluene (1 mL) was
added to a solution of 8 (194 mg, 1.0 mmol) in CH2Cl2 (7 mL) and the mixture was
.
stirred for 30 min at rt. The solution was cooled to 0 °C, BF3 Et2O (2.0 mL, ca. 12
mmol) was added and the mixture was stirred for 8 d at rt. A 10 % solution of
NaHCO3 (12 mL) was added, the organic layer was separated and the aqueous layer
was extracted with CH2Cl2 (4×10 mL). The combined organic layers were dried
(Na2SO4), concentrated in vacuo and the residue was purified by fc (3 cm,
cyclohexane : EtOAc = 4 : 1, 20 mL, Rf = 0.13). Colorless oil, yield 91.4 mg (22 %).
C24H27NO7 (409.5). MS (EI): m/z = 409 [M], 318 [M-PhCH2], 274. [M-PhCH2CO2]. IR:
 [cm-1] = 2925 (C-H), 1736 (C=O ester), 1694 (C=O carbamate), 1207, 1043 (C-O).
1H NMR (CDCl3): δ [ppm] = 1.64 - 1.78 (m, 2H N(CH2CH2)2), 2.02 (td, J = 13.2/4.9
Hz, 1H, N(CH2CH2)2), 2.09 (dd, J = 14.3/2.3 Hz, 1H, N(CH2CH2)2), 2.61 (dd, J =
18

15.3/4.4 Hz, 1H, CH2CO2CH3), 2.69 (dd, J = 15.3/8.7 Hz, 1H, CH2CO2CH3), 2.71 (dd,
J = 15.8/3.3 Hz, 1H, ArCH2CH), 2.78 (dd, J = 15.8/10.5 Hz, 1H, ArCH2CH), 3.14 (td,
J = 13.1/2.8 Hz, 1H, N(CH2CH2)2), 3.24 (td, J = 13.1/2.8 Hz, 1H, N(CH2CH2)2), 3.73
(s, 3H, CO2CH3), 4.04-4.15 (m, 2H, N(CH2CH2)2), 4.21 - 4.3 (m, 1H, ArCH2CH), 5.17
(s, 2H, PhCH2O), 7.04 - 7.09 (m, 2H, arom.), 7.14 - 7.22 (m, 2H, arom.), 7.29 - 7.41
(m, 5H, arom.).
5.2.7. Methyl (±)-2-(3,4-dihydrospiro[[2]benzopyran-1,4'-piperidin]-3yl)acetate
(14)
13 (91.4 mg, 0.223 mmol) was dissolved in methanol (17 mL). Pd/C (8.7 mg) was
added and the mixture was stirred under H2 atmosphere for 20 h. The catalyst was
removed by filtration and the solution was concentrated in vacuo. Colorless oil, yield
56.2 mg (89 %), Rf = 0.04 (cyclohexane : EtOAc = 4 : 1). C16H21NO3 (275.35). MS
(EI): m/z = 275 [M], 219 [M-CHNHCH2CH2]. IR:  [cm-1] = 2925 (C-H), 1735 (C=O),
1
1155, 1044 (C-O). H NMR (CDCl3): δ [ppm] = 1.68 (dd, J = 15.7/2.2 Hz, 1H,
N(CH2CH2)2), 1.77 (td, J = 13.4/4.7 Hz, 1H, N(CH2CH2)2), 2.05 - 2.13 (m, 2H,
N(CH2CH2)2), 2.4 (s, 1H, NH), 2.61 (dd, J = 15.1/4.5 Hz, 1H, CH2CO2CH3), 2.65 -
2.74 (m, 2H, N(CH2CH2)2), 2.76 (dd, J = 15.7/10.4 Hz, 1H, CH2CO2CH3), 2.88 - 3.04
(m, 3H, ArCH2 (2H), N(CH2CH2)2 (1H)), 3.11 (td, J = 12.2/2.1 Hz, 1H, N(CH2CH2)2),
3.74 (s, 3H, CO2CH3), 4.21 - 4.28 (m, 1H, ArCH2CH), 7.06 (d, J = 7.5 Hz, 1H, arom.),
7.11 - 7.23 (m, 3H, arom.).
5.2.8. (±)-2-(1'-Acetyl-3,4-dihydrospiro[[2]benzopyran-1,4'-piperidin]-3-
yl)ethanol (15)
Under N2, 12 (602 mg, 1.9 mmol) was dissolved in THF (15 mL). The mixture was
cooled to 0 °C and a solution of LiBH4 (3.8 mL, 7.6 mmol, 2 M in THF) was added.
19

The mixture was stirred at rt for 20 h, then is was concentrated in vacuo. The residue
was dissolved in water (10 mL), 0.5 M HCl was added and the mixture was extracted
with CH2Cl2 (4×12 mL). The combined organic layers were dried (Na2SO4),
concentrated in vacuo and the residue was purified by fc (2 cm, CH2Cl2 : methanol =
95 : 5, 10 mL, Rf = 0.24). Colorless oil, yield 415 mg (76 %). C17H23NO3 (289.4). MS
(EI): m/z = 289 [M], 246 [M-COCH3]. IR:  [cm-1] = 3385 (O-H), 2923 (C-H), 1617
1
(C=O amide). H NMR (CDCl3): δ [ppm] = 1.63 – 2.03 (m, 6H, CH2CH2OH (2H),
N(CH2CH2)2 (4H)), 2.08 (s, 3H, NCOCH3), 2.60 (d, J = 15.9 Hz, 1H, ArCH2), 2.77 (dd,
J = 15.9/11.1 Hz, 1H, ArCH2), 2.81 – 2.92 (m, 1H, N(CH2CH2)2), 3.37 – 3.49 (m, 1H,
N(CH2CH2)2), 3.66 – 3.71 (m, 1H, N(CH2CH2)2), 3.79 – 3.91 (m, 2H, CH2OH), 3.92 –
4.04 (m, 1H ArCH2CH), 4.49 – 4.57 (m, 1H, N(CH2CH2)2), 6.97 – 7.06 (m, 2H, arom.),
7.07 – 7.15 (m, 2H, arom.). A signal for the OH proton is not seen in the spectrum.
5.2.9. (±)-2-(3,4-Dihydrospiro[[2]benzopyran-1,4'-piperidin]-3-yl)ethanol (16)
A solution of 15 (346 mg, 1.2 mmol) in 2 M NaOH (20 mL) was heated to reflux for 3
h. The mixture was cooled to rt and extracted with CH2Cl2 (3×10 mL). The combined
organic layers were dried (K2CO3) and concentrated in vacuo. The product was
directly used without further purification. Colorless oil, yield 157.3 mg (53 %), Rf =
0.03 (CH2Cl2 : methanol = 95 : 5). C15H21NO2 (247.3). MS (EI): m/z = 247 [M], 228
[M-H3O+], 199 [M-H3O+-NHCH2], 184 [M-H3O+-NH2CH2CH2]. IR:  [cm-1] = 3345 (O-
1
H) (N-H), 2937 (C-H), 1488, 1422 (C-H), 1043 (C-O). H NMR (CDCl3): δ [ppm] =
1.62 – 2.11 (m, 6H, NH(CH2CH2)2 (4H), CH2CH2OH (2H)), 2.55 (dd, J = 15.8/2.6 Hz,
1H, PhCH2), 2.75 (dd, J = 15.8/11.2 Hz, 1H, PhCH2), 2.85 – 3.15 (m, 4H,
NH(CH2CH2)2), 3.81 – 3.88 (m, 2H, CH2CH2OH), 3.92 – 4.01 (m, 1H, PhCH2CH), 7.0
(d, J = 7.4 Hz, 1H, arom.) 7.05 – 7.17 (m, 3H, arom.). Signals for the OH and NH
protons are not seen in the spectrum.
20

5.2.10. Methyl (±)-2-[1'-(3-phenylpropyl)-3,4-dihydrospiro[[2]benzopyran-1,4'-
piperidin]-3-yl]acetate (17e)
1-Bromo-3-phenylpropane (44.8 mg, 0.23 mmol) and K2CO3 (37 mg, 0.27 mmol)
were added to a solution of 14 (50.8 mg, 0.18 mmol) in CH3CN (8 mL). The mixture
was heated to reflux for 4 h. The residue was filtered and concentrated in vacuo. The
residue was purified by fc (1 cm, cyclohexane : EtOAc = 1 : 1 + 0.1 % NH3, 5 mL, Rf
= 0.36). Colorless oil, yield 49.2 mg (69 %). C25H31NO3 (393.53). MS (EI): m/z = 393
[M], 288 [M-PhCH2CH2]. IR:  [cm-1] = 2944, 2812 (C-H), 1736 (C=O), 1155, 1046
(C-O). 1H NMR (CDCl3): δ [ppm] = 1.69 (dd, J = 13.5/2.6 Hz, 1H, N(CH2CH2)2), 1.82 -
1.91 (m, 3H, N(CH2CH2)2, (1H), CH2CH2Ph (2H)), 2.09 (dd, J = 14.3/2.5 Hz, 1H,
N(CH2CH2)2) 2.15-2.28 (m, 2H, N(CH2CH2)2 (1H), N(CH2CH2CH2Ph (1H)), 2.34 -
2.44 (m, 3H, N(CH2CH2)2 (2H), NCH2CH2CH2Ph (1H)), 2.59 (dd, J = 14.8/4.6 Hz, 1H,
CHCH2CO2CH3), 2.63 - 2.68 (m, 3H, CHCH2CO2CH3 (1H), NCH2CH2CH2Ph (2H)),
2.69 - 2.79 (m, 4H, ArCH2CH (2H), N(CH2CH2)2 (2H)), 3.71 (s, 3H, CO2CH3), 4.20 –
4.25 (m, 1H, ArCH2CH), 7.05 (d, J = 7.3 Hz, 1H, arom.), 7.11 – 7.23 (m, 6H, arom.),
7.25 - 7.30 (m, 2H, arom.). Purity determined by HPLC: 96 %.
5.2.11. (±)-2-(1'-Ethyl-3,4-dihydrospiro[[2]benzopyran-1,4'-piperidin]-3-
yl)ethanol (18a)
1-Bromoethane (44.6 mg, 0.40 mmol) and K2CO3 (69 mg, 0.5 mmol) were added to a
solution of 16 (81.1 mg, 0.33 mmol) in CH3CN (15 mL). The mixture was heated to
reflux for 4 h, then it was filtered and concentrated in vacuo. The residue was purified
by fc (1 cm, CH2Cl2 : methanol = 95 : 5 + 0.1 % NH3, 5 mL, Rf = 0.19). Colorless oil,
yield 43.5 mg, (48 %). C17H25NO2 (275.4). MS (ESI): m/z = 276 [MH+]. IR:  [cm-1] =
1
3395 (O-H), 2926 (C-H), 1061, 1045 (C-O). H NMR (CDCl3): δ [ppm] = 1.07 (t, J =
21

7.2 Hz, 3H, CH2CH3), 1.68 (dd, J = 13.2/2.3 Hz, 1H, N(CH2CH2)2), 1.79 – 1.93 (m,
3H, N(CH2CH2)2 (1H), CH2CH2OH (2H)), 2.05 (dd, J = 14.4/2.7 Hz, 1H, N(CH2CH2)2),
2.13 – 2.29 (m, 3H, N(CH2CH2)2 (1H), N(CH2CH2)2 (2H)), 2.43 (q, J = 7.2 Hz, 2H,
NCH2CH3), 2.56 (dd, J = 15.9/2.6 Hz, 1H, ArCH2CH), 2.73 – 2.84 (m, 3H,
N(CH2CH2)2 (2H), ArCH2CH (1H)), 3.84 (t, J = 5.5 Hz, 2H, CH2CH2OH), 3.92 – 3.99
(m, 1H, ArCH2CH), 6.99 (d, J = 7.3 Hz, 1H, arom.) 7.05 – 7.16 (m, 3H, arom.). A
signal for the OH proton is not seen in the spectrum. Purity determined by HPLC: 98
%.
5.2.12. (±)-2–(1'-Butyl-3,4-dihydrospiro[[2]benzopyran-1,4'-piperidin]-3-
yl)ethanol (18b)
1-Bromobutane (27.4 mg, 0.20 mmol) and K2CO3 (33 mg, 0.24 mmol) were added to
a solution of 16 (39.5 mg, 0.16 mmol) in CH3CN (10 mL). The mixture was heated to
reflux for 4 h, then it was filtered and concentrated in vacuo. The residue was purified
by fc (1 cm, cyclohexane : EtOAc = 1 : 1 + 0.1 % NH3, 5 mL, Rf = 0.22). Colorless oil,
yield 20.3 mg (42 %). C19H29NO2 (303.5). MS (EI): m/z = 303 [M], 260 [M-(CH2)2CH3]
1
IR:  [cm-1] = 3392 (O-H), 2929, 2820 (C-H), 1098, 1044 (C-O). H NMR (CDCl3): δ
[ppm] = 0.87 (t, J = 7.3 Hz, 3H, (CH2)3CH3), 1.27 (sext., J = 7.3 Hz, 2H
(CH2)2CH2CH3), 1.42 – 1.50 (m, 2H, CH2CH2CH3), 1.53 – 1.60 (s, 1H, OH), 1.67 (dd,
J = 13.2/2.4 Hz, 1H, N(CH2CH2)2), 1.80 – 1.93 (m, 3H, N(CH2CH2)2 (1H), CH2CH2OH
(2H)), 2.04 (dd, J = 14.4/2.6 Hz, 1H, N(CH2CH2)2), 2.13 – 2.29 (m, 3H, N(CH2CH2)2
(1H), N(CH2CH2)2 (2H)), 2.31 – 2.36 (m, 2H, NCH2(CH2)2CH3), 2.56 (dd, J = 16.0/2.6
Hz, 1H, ArCH2CH), 2.74 – 2.81 (m, 3H, N(CH2CH2)2 (2H), ArCH2CH (1H)), 3.84 (t, J
= 5.5 Hz, 2H, CH2CH2OH), 3.92 – 3.99 (m, 1H, ArCH2CH), 6.99 (d, J = 7.4 Hz, 1H,
arom.), 7.05 – 7.16 (m, 3H, arom.). Purity determined by HPLC: 97 %.
22

5.2.13. (±)-2-(1'-Octyl-3,4-dihydrospiro[[2]benzopyran-1,4'-piperidin]-3-
yl)ethanol (18c)
1-Bromooctane (116 mg, 0.6 mmol) and K2CO3 (104 mg, 0.75 mmol) were added to
a solution of 16 (122 mg, 0.49 mmol) in CH3CN (15 mL). The mixture was heated to
reflux for 4 h, then it was filtered and concentrated in vacuo. The residue was purified
by fc (2.5 cm, cyclohexane : EtOAc = 1 : 1 + 0.1 % NH3, 10 mL, Rf = 0.30). Colorless
oil, yield 92.2 mg, (53 %). C23H37NO2 (359.6). MS (EI): m/z = 359 [M], 260 [M-
(CH2)6CH3]. IR:  [cm-1] = 3214 (O-H), 2924, 2856 (C-H), 1098, 1043 (C-O). 1H NMR
(CDCl3): δ [ppm] = 0.88 (t, J = 6.8 Hz, 3H, (CH2)7CH3), 1.22 – 1.32 (m, 10H,
(CH2)5CH3), 1.48 – 1.55 (m, 2H, CH2CH2(CH2)5CH3), 1.63 – 1.72 (s, 1H, OH) 1.73
(dd, J = 13.7/2.7, 1H, N(CH2CH2)2), 1.83 – 2.0 (m, 3H, N(CH2CH2)2 (1H), CH2CH2OH
(2H)), 2.08 (dd,J = 14.4/2.6, 1H, N(CH2CH2)2), 2.18 – 2.33 (m, 3H, N(CH2CH2)2
(1H), N(CH2CH2)2 (2H)), 2.36 – 2.41 (m, 2H, NCH2(CH2)6CH3), 2.62 (dd, 1H, J =
13.3/2.6, PhCH2CH), 2.78 – 2.87 (m, 3H, N(CH2CH2)2 (2H), PhCH2CH (1H)), 3.90 (t,
J = 5.5 Hz, 2H, CH2CH2OH), 3.98 – 4.05 (m, 1H, PhCH2CH), 7.05 (d, J = 7.2, 1H,
arom.), 7.12 – 7.22 (m, 3H, arom.). Purity determined by HPLC: 99 %.
5.2.14. (±)-2-(1'-Benzyl-3,4-dihydrospiro[[2]benzopyran-1,4'-piperidin]-3-
yl)ethanol (18d)
Benzyl bromide (68.4 mg, 0.40 mmol) and K2CO3 (62 mg, 0.45 mmol) were added to
a solution of 16 (68.3 mg, 0.28 mmol) in CH3CN (10 mL). The mixture was heated to
reflux for 20 h, then it was filtered and the crude mixture was concentrated in vacuo.
The residue was purified by fc (2.5 cm, cyclohexane : EtOAc = 1 : 1 + 0.1 % NH3, 10
mL, Rf = 0.14). Colorless oil, yield 15.7 mg, (17 %). C22H27NO2 (337.5). MS (EI): m/z
= 337 [M], 246 [M – CH2Ph], 91 [CH2Ph]. IR:  [cm-1] = 3394 (O-H), 2939, 2821 (C-
1
H), 1094, 1049 (C-O), 741, 700 (C-H). H NMR (CDCl3): δ [ppm] = 1.71 (dd, J =
23

13.4/2.7 Hz, 1H, N(CH2CH2)2), 1.84 – 2.01 (m, 3H, N(CH2CH2)2 (1H), CH2CH2OH
(2H)), 2.08 (dd, J = 14.2/4.5 Hz, 1H, N(CH2CH2)2), 2.22 (td, J = 13.1/4.4 Hz, 1H,
N(CH2CH2)2), 2.30 – 2.44 (m, 2H, N(CH2CH2)2), 2.61 (dd, J = 15.9/2.7 Hz, 1H,
ArCH2CH), 2.72 – 2.83 (m, 2H, N(CH2CH2)2), 2.83 (dd, J = 15.9/11.3 Hz, 1H,
ArCH2CH), 3.57 (s, 2H, NCH2Ph), 3.89 (t, J = 5.5 Hz, 2H, CH2CH2OH), 3.96 – 4.05
(m, 1H, ArCH2CH), 7.04 (d, J = 7.0 Hz, 1H, arom.), 7.10-7.40 (m, 8H, arom.). A signal
for the OH proton is not seen in the spectrum. Purity determined by HPLC: 98 %.
5.2.15. (±)-2-[1'-(3-Phenylpropyl)-3,4-dihydrospiro[[2]benzopyran-1,4'-piperidin]-
3-yl]ethanol (18e)
1-Bromo-3-phenylpropane (156 mg, 0.78 mmol) and K2CO3 (133 mg, 0.96 mmol)
were added to a solution of 16 (158 mg, 0.64 mmol) in CH3CN (15 mL). The mixture
was heated to reflux for 4 h, then it was filtered and concentrated in vacuo. 0.5 M HCl
(10 mL) was added and the solution was washed with EtOAc (2×5 mL). The aqueous
layer was alkalised, extracted with CH2Cl2 (3×10 mL) and the combined CH2Cl2
layers were concentrated in vacuo. The residue was purified by fc (2.5 cm,
cyclohexane : EtOAc = 1 : 1 + 0.1 % NH3, 10 mL, Rf = 0.25). Colorless oil, yield 164.8
mg (70 %). C24H31NO2 (365.5). MS (EI): m/z = 365 [M], 260 [M – (CH2)2C6H5]. IR: 
1
[cm-1] = 3024 (O-H), 2938, 2822 (C-H), 1062, 1045 (C-O), 753, 689 (C-H). H NMR
(CDCl3): δ [ppm] = 1.67 (dd, J = 13.3/2.6 Hz, 1H, N(CH2CH2)2), 1.76 – 1.91 (m, 5H,
N(CH2CH2)2 (1H), CH2CH2OH (2H), CH2CH2Ph (2H)), 2.03 (dd, J = 14.3/2.6 Hz, 1H,
N(CH2CH2)2), 2.15 (td, J = 12.9/4.2 Hz, 1H, N(CH2CH2)2), 2.20 – 2.29 (m, 2H,
NCH2(CH2)2Ph), 2.35 – 2.40 (m, 2H, N(CH2CH2)2), 2.52 – 2.61 (m, 3H, ArCH2CH
(1H), N(CH2)2CH2Ph (2H)), 2.63 (s, 1H, OH), 2.71 – 2.81 (m, 3H, N(CH2CH2)2 (2H),
ArCH2CH (1H)), 3.79 – 3.88 (m, 2H, CH2CH2OH), 3.91 – 4.00 (m, 1H, ArCH2CH),
24

6.99 (d, J = 7.3 Hz, 1H, arom.), 7.04 – 7.15 (m, 5H, arom.), 7.18 – 7.38 (m, 3H,
arom.). Purity determined by HPLC: 99 %.
5.2.16. Methyl cis-(±)-2-[1-(bromomethyl)-3,4-dihydro-1H-2-benzopyran-3-
yl]acetate (20a)
Under N2, 8 (194 mg, 1.0 mmol) was dissolved in CH2Cl2 abs. (14 mL).
Bromoacetaldehyde dimethyl acetal (19a, 507 mg, 3.0 mmol, 50 % in toluene) was
added and the mixture was stirred at rt for 30 min. Then solution was cooled to 0 °C,
BF3•Et2O (1.3 mL, 8 mmol) was added and the mixture was stirred at rt for 2 d. 0.5 M
HCl (15 mL) was added and the mixture was extracted with CH2Cl2 (3×15 mL). The
combined organic layers were dried (Na2SO4), concentrated in vacuo and the residue
was purified by fc (4 cm, cyclohexane : EtOAc = 9 : 1, 20 mL, Rf = 0.44). Colorless
oil, yield 258 mg (86 %). C13H15BrO3 (299.2). MS (EI): m/z = 300 [81Br-M],298 [79 Br-
1
M]. IR:  [cm-1] = 2950 (C-H), 1734 (C=O), 1156, 1092 (C-O), 745 (C-H). H NMR
(CDCl3): δ [ppm] = 2.62 (dd, J = 15.5/5.6 Hz, 1H, CH2CO2CH3), 2.72 – 2.88 (m, 3H,
CH2CO2CH3 (1H), ArCH2 (2H)), 3.64 (dd, J = 10.9/5.9 Hz, 1H, CH2Br), 3.74 (s, 3H,
CO2CH3), 3.87 (dd, J = 10.9/2.7 Hz, 1H, CH2Br), 4.14 – 4.22 (m, 1H, ArCH2CH), 5.09
(dd, J = 5.1/1.9 Hz, 1H, ArCHO), 7.07 – 7.14 (m, 2H, arom.), 7.20 – 7.25 (m, 2H,
arom.). The relative configuration was determined by NOE spectra.
5.2.17. Methyl cis-(±)-2-[1-(2-chloroethyl)-3,4-dihydro-1H-2-benzopyran-3-
yl]acetate (20b)
Under N2, 8 (388 mg, 2.0 mmol) was dissolved in CH2Cl2 abs. (14 mL).
3-Chloropropionaldehyde diethyl acetal (19b, 833 mg, 5.0 mmol in 1.5 mL toluene)
was added and the mixture was stirred for 30 min at rt. The solution was cooled to 0
°C, BF3•Et2O (2.5 mL, ca. 16 mmol) was added and the mixture was stirred at rt for 4
25

d. 0.5 M HCl (15 mL) was added and the mixture was extracted with CH2Cl2 (3×15
mL). The combined organic layers were dried (Na2SO4), concentrated in vacuo and
the residue was purified by fc (3 cm, cyclohexane : EtOAc 9 : 1, 20 mL, Rf = 0.33).
Pale yellow oil, yield 1739 mg (32 %). C14H17ClO3 (268.47). MS (EI): m/z = 205 [M-
CH2CH2Cl], 129 [C10H9], 117 [C9H9]. IR:  [cm-1] = 2951 (C-H), 1738 (C=O), 1157,
1
1094 (C-O), 743 (C-H). H NMR (CDCl3): δ [ppm] = 2.09-2.18 (m, 1H, CH2CHCl),
2.40-2.44 (m, 1H, CH2CH2Cl), 2.59 (dd, J = 15.2/5.4 Hz, 1H, CH2CO2CH3), 2.62-2.78
(m, 2H, PhCH2), 2.69 (dd, J = 15.2/7.8 Hz, 1H, CH2CO2CH3), 3.57-3.64 (m, 1H,
CH2Cl), 3.73 (s, 3H, CO2CH3), 3.75-3.79 (m, 1H, CH2Cl), 4.10-4.18 (m, 1H,
PhCH2CH), 4.95 (d, J = 7.9 Hz, 1H, PhCHO) 7.07-7.22 (m, 4H, arom.). The relative
configuration was determined by NOE spectra.
5.2.18.
Ethyl
cis-(±)-3-[1-(methoxycarbonyl)methyl]-3,4-dihydro-1H-2-
benzopyran-1-carboxylate (20c)
Under N2, 8 (486 mg, 2.5 mmol) was dissolved in CH2Cl2 (10 mL). Ethyl 2,2-
diethoxyacetate (19c, 1.32 g, 7.5 mmol, 50 % in toluene) was added and the mixture
was stirred for 30 min at rt. Then solution was cooled to 0 °C, BF3•Et2O (3.2 mL, 20
mmol) was added and the mixture was stirred at rt for 4 d. 0.5 M HCl (17.5 mL) was
added and the mixture was extracted with CH2Cl2 (3×12.5 mL). The combined
organic layers were dried (Na2SO4), concentrated in vacuo and the residue was
purified by fc (4 cm, petroleum ether : EtOAc = 4 :1, 20 mL, Rf = 0.48). Colorless oil,
yield 618 mg (99 %). C15H18O5 (278.3). MS (ESI): m/z = 278 [M]. IR:  [cm-1] = 2981,
1
2953 (C-H), 1734 (C=O), 1159, 1105 (C-O), 749 (C-H). H NMR (CDCl3): δ [ppm] =
1.29 (t, J = 7.1 Hz, 3H, CO2CH2CH3), 2.66 (dd, J = 15.9/5.7 Hz, 1H, CH2CO2CH3),
2.77 (dd, J = 15.7/2.7 Hz, 1H, ArCH2), 2.88 (dd, J = 15.9/7.3 Hz, 1H, CH2CO2CH3),
2.94 (dd, J = 15.7/11.2 Hz, 1H, ArCH2), 3.72 (s, 3H, CO2CH3), 4.18 – 4.29 (m, 3H,
26

CO2CH2CH3 (2H), ArCH2CH (1H)), 5.44 (s, 1H, ArCHO), 7.09 – 7.34 (m, 4H, arom.).
5.2.19. Dimethyl cis-(±)-3,4-dihydro-1H-2-benzopyran-1,3-diacetate (20d)
Under N2, 8 (486 mg, 2.5 mmol) was dissolved in CH2Cl2 (10 mL). Methyl 3,3-
dimethoxypropionat (19d, 1.11 g, 7.5 mmol, 50 % in toluene) was added and the
mixture was stirred for 30 min at rt. The solution was cooled to 0 °C, BF3•Et2O (3.2
mL, 20 mmol) was added and the mixture was stirred at rt for 4 d. 0.5 M HCl (17.5
mL) was added and the mixture was extracted with CH2Cl2 (3×12.5 mL). The
combined organic layers were dried (Na2SO4), concentrated in vacuo and the residue
was purified by fc (4 cm, petroleum ether : EtOAc = 4:1, 20 mL, Rf = 0.37). colorless
solid, yield 582.8 mg (84 %), mp. 62.9 °C. C15H18O5 (278.3). MS (EI): m/z = 278 [M],
+
205 [M-CH2COOCH3], 145 [M-(CH2COOCH3+COOCH3 )]. IR:  [cm-1] = 2947, 2879
1
(C-H), 1743, 1723 (C=O), 1159, 1103 (C-O), 750 (C-H). H NMR (CDCl3): δ [ppm] =
2.57 (dd, J = 15.3/5.9 Hz, 1H, ArCH2CHCH2CO2CH3), 2.68 (dd, J = 15.1/9.2 Hz, 1H,
ArCH2), 2.70 (dd, J = 15.3/7.4 Hz, 1H, ArCH2CHCH2CO2CH3), 2.76 – 2.81 (m, 2H,
ArCHCH2CO2CH3), 2.94 (dd, J = 15.1/3.7 Hz, 1H, ArCH2), 3.70 (s, 3H, CO2CH3),
3.71 (s, 3H, CO2CH3), 4.10 – 4.18 (m, 1H, ArCH2CH), 5.23 (dd, J = 9.1/3.7 Hz, 1H,
ArCHO), 7.01 – 7.21 (m, 4H, arom.). The relative configuration was determined by
NOE spectra.
5.2.20. Methyl cis-(±)-2-[1-(azidomethyl)-3,4-dihydro-1H-2-benzopyran-3-
yl]acetate (20e)
20a (330 mg, 1.1 mmol) and NaN3 (286 mg, 4.4 mmol) were dissolved in DMF (20
mL). The mixture was heated to 60-70 °C for 24 h. After cooling to rt, water (180 mL)
was added and the mixture was extracted with Et2O (5 x 60 mL). The combined
organic layers were extracted with water (3 x 150 mL), dried (Na2SO4) and
27

concentrated in vacuo. The residue was purified by fc (4 cm, cyclohexane : EtOAc =
9 :1, 20 mL, Rf = 0.19). Colorless oil, yield 83.2 mg (29 %). C13H15N3O3 (261.3). MS
(EI): m/z = 261 [M], 233 [M-N2], 205 [M- CH2N3]. IR:  [cm-1] = 2951 (C-H); 2098 (-
N3), 1735 (C=O), 1157, 1099 (C-O), 746 (C-H). 1H NMR (CDCl3): δ [ppm] = 2.62 (dd,
J = 15.6/5.4 Hz, 1H, CH2CO2CH3), 2.72 – 2.91 (m, 3H, CH2CO2CH3 (1H), ArCH2
(2H)), 3.48 (dd, J = 13.1/ 6.4 Hz, 1H, CH2N3), 3.64 (dd, J = 13.1/2.7 Hz, 1H, CH2N3),
3.73 (s, 3H, CO2CH3), 4.15 – 4.23 (m, 1H, ArCH2CH), 5.08 (d, J = 5.0 Hz, 1H,
ArCHO), 7.0 – 7.25 (m, 4H, arom.).
5.2.21.
Methyl
cis-(±)-2-{1-[(-piperidin-1-yl)methyl]-3,4-dihydro-1H-2-
benzopyran-3-yl}acetate (21b)
20a (71.3 mg, 0.26 mmol), piperidine (0.03 mL, 0.3 mmol), K2CO3 (55 mg, 0.4 mmol)
and a small amount of tetrabutylammonium iodide were dissolved in CH3CN (10 mL).
The mixture was heated to reflux for 20 h. The residue was filtered, concentrated in
vacuo, the residue was dissolved in 0.5 M HCl (10 mL) and the mixture was extracted
with EtOAc (2x5 mL). The aqueous layers were alkalized with 0.5 M NaOH and
extracted with CH2Cl2 (3×10 mL). The combined organic layers were dried (K2CO3)
and concentrated in vacuo. The residue was purified by fc (1 cm, CH2Cl2 : CH3OH =
98 : 2 + 0.1 % NH3, 5 mL, Rf = 0.13 Pale yellow oil, yield 12.5 mg (16 %). C18H25NO3
+
(303.4) MS (EI): m/z = 303 [M], 98 [CH2N(CH2CH2)2CH2 ]. IR:  [cm-1] = 2931, 2852
(C-H), 1735 (C=O), 1154, 1089 (C-O), 743 (C-H). 1H NMR (CDCl3): δ [ppm] = 1.40 –
1.51 (m, 2H, N(CH2CH2)2CH2), 1.59 – 1.71 (m, 4H, N(CH2CH2)2CH2), 2.50 – 2.87 (m,
9H, N(CH2CH2)2CH2 (4H), CH2CO2CH3 (2H), ArCH2 (2H), NCH2 (1H)), 2.95 (d, J =
12.2 Hz, 1H, NCH2), 3.71 (s, 3H, CO2CH3), 4.08 – 4.16 (m, 1H, ArCH2CH), 5.02 (d, J
= 5.5 Hz, 1H, ArCHO), 7.02 – 7.28 (m, 4H, arom.). The relative configuration was
determined by a NOESY spectrum. Purity determined by HPLC: 96 %.
28

5.2.22. Methyl cis-(±)-2-{1-[(4-phenylpiperidin-1-yl)methyl]-3,4-dihydro-1H-2-
benzopyran-3-yl}acetate (21c)
20a (274 mg, 1.02 mmol), 4-phenylpiperidine (242 mg, 1.5 mmol), K2CO3 (207 mg,
1.5 mmol) and a small amount of tetrabutylammonium iodide were dissolved in
CH3CN (20 mL). The mixture was heated to reflux for 20 h. Then it was filtered,
concentrated in vacuo, the residue was dissolved in 0.5 M HCl (10 mL) and extracted
with EtOAc (2x5 mL). The aqueous layers were alkalized with 0.5 M NaOH and
extracted with CH2Cl2 (3×10 mL). The combined organic layers were dried (K2CO3),
concentrated in vacuo and the residue was purified by fc (2.5 cm, cyclohexane :
EtOAc = 1 : 1 + 0.1 % NH3, 10 mL, Rf = 0.22). Pale yellow oil, yield 40.8 mg (11 %).
C24H29NO3 (379.5). MS (EI): m/z = 380 [M], 174 [PhCH(CH2CH2)2NCH2]. IR:  [cm-1]
1
= 3025, 2929 (C-H), 1736 (C=O), 1155, 1092 (C-O), 744, 699 (C-H). H NMR
(CDCl3): δ [ppm] = 1.72 – 1.84 (m, 4H, N(CH2CH2)2CHPh), 2.15 – 2.29 (m, 2H,
N(CH2CH2)2CHPh), 2.39 – 2.49 (m, 1H, N(CH2CH2)2CHPh), 2.54 (dd, J = 15.2/5.3
Hz, 1H, CH2CO2CH3), 2.64 – 2.81 (m, 4H, CH2CO2CH3 (1H), ArCH2CH (2H), NCH2
(1H)), 2.92 (dd, J = 13.4/3.5 Hz, 1H NCH2), 3.06 (dd, J = 10.6/1.6 Hz, 1H,
N(CH2CH2)2CHPh), 3.20 (dd, J = 11.2/1.2 Hz, 1H, N(CH2CH2)2CHPh), 3.64 (s, 3H,
CH2CO2CH3), 4.04 – 4.12 (m, 1H, ArCH2CH), 4.96 (dd, J = 7.3/2.4 Hz, 1H, ArCHO),
7.00 – 7.28 (m, 9H, arom.). The relative configuration was determined by a NOESY
spectrum. Purity determined by HPLC: 98 %.
5.2.23. Methyl cis-(±)-2-{1-[2-(pyrrolidin-1-yl)ethyl]-3,4-dihydro-1H-2-
benzopyran-3-yl}acetate (22a)
20b (102 mg, 0.38 mmol), pyrrolidine (0.05 mL, 0.43 mmol), K2CO3 (69 mg, 0.5
mmol) and a small amount of tetrabutylammonium iodide were dissolved in CH3CN
29