Site-selective synthesis of 1,3-dioxin-3-ones: Via a gold(i) catalyzed cascade reaction

Article abstract of DOI:10.1039/d0cc02703k

A novel gold(i)-catalyzed protocol for the synthesis of 4H-1,3-dioxin-3-ones is presented. The protocol exploits a metal induced cascade sequence involving a [3,3]-sigmatropic rearrangement followed by regioselective O-annulation reactions. A wide range of oxygen-based heterocyclic scaffolds (21 examples) were achieved in excellent yield (up to 80percent) and a detailed computational investigation as well as deuterium-labelling investigations enabled all the plausible reaction pathways to be mapped and the rationalization of the recorded regioselectivity.

Full text of DOI:10.1039/d0cc02703k

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DOI: 10.1039/D0CC02703K
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Site-selective Synthesis of 1,3-Dioxin-3-ones via a Gold(I)
Catalyzed Cascade Reaction
Juzeng An,a† Riccardo Pedrazzani,a Magda Monari,a Marta Marin-Luna,b† Carlos Silva Lopez,b,c*
Received 00th January 20xx,
Accepted 00th January 20xx
Marco Bandinia,d
*
DOI: 10.1039/x0xx00000x
stoichiometric protocols (i.e. lithiation/alkylation, [4+2]-
cycloadditions) with only few notable catalytic exceptions.6
Therefore, the request for flexible, selective and
environmentally benign synthetic methodologies for their
preparation has been and continues to be widely investigated.
In continuation with our ongoing commitment towards the
realization of gold catalyzed electrophilic activations of
alkynes,7,8 we envisioned the possibility to realize a new direct
synthetic protocol of densely functionalized 1,3-dioxin-3-ones
via [Au(I)]-assisted manipulation of readily available
propargylic-ketoesters 1. In particular, an initial intramolecular
[3,3]-sigmatropic rearrangement9 could lead to the
corresponding carboxyallene intermediate 1’ that might
undergo a rapid annulation reaction delivering the desired six-
membered ring 2 (Figure 1c). However, the present working
plan poses several important regiochemical interrogatives due
to the multiple electrophilic as well as nucleophilic sites present
in the [Au+]-1 adduct.
ABSTRACT: A novel gold(I)-catalyzed protocol for the synthesis of
4H-1,3-dioxin-3-ones is presented. The protocol exploits a metal
induced cascade sequence involving
a
[3,3]-sigmatropic
rearrangement followed by regioselective O-annulation reactions.
A wide range of oxygen-based heterocyclic scaffolds (21 examples)
were achieved in excellent yield (up to 80%) and a detailed
computation as well as deuterium-labelling investigations enabled
all the plausible reaction pathways to be mapped and the
rationalization of the recorded regioselectivity.
Homogenous gold catalysis has revolutionized the realm of
the
manipulation
of
unsaturated
unfunctionalized
hydrocarbons in just twenty years.1 In particular, the site-
selective electrophilic activation of C-C double and triple bonds
enabled a plethora of single- as well as multi-step synthetic
sequences in a convenient manner.
The synthesis of densely functionalized heterocycles
deeply benefited by this advent, exploiting the unique
functional groups tolerance exerted by cationic [Au(I)]
complexes and the realization of new C-C and C-X annulation
events.2 In this context, the 1,3-dioxin-3-one scaffold (A, Figure
1a) is of particular relevance since it identifies synthetically
flexible building blocks for organic transformations such as:
ketene chemistry, aromatization reactions, rearrangements,
cycloadditions and total syntheses.3 In addition, aromatic
analogous of the 1,3-dioxin-3-one scaffolds (Figure 1b), namely
dioxanones4 are common motifs in numerous natural
compounds (i.e. chlorotheolide family) that display intense
antiproliferative actions on several tumor cell lines.5
Figure 1. a) The 1,3-dioxin-3-one scaffold (A) and relative synthetic manipulations; b) a
representative example of natural occurring compound comprising the dioxanones core;
c) the present gold(I)-catalyzed synthetic approach to 2.
HO
b)
aromatization reactions
O
a)
Me
’R R’’
O
O
O
O
O
O
O
O
Me
R,R’,R’’ = Me
R’’’ = H
O
R
O
O
O
R’’’
Cl
A
O
Me
C7H15
cycloaddition reactions
Notably, despite the undoubted transversal utility of this
class of building blocks, their preparation still relies on
Chlorotheolide B
R2
R2
working plan
R3
[+Au]
[Au+]
R3
O
R3
O
O
O
O
a Dipartimento di Chimica “Giacomo Ciamician”, Alma Mater Studiorum – Università
di Bologna, via Selmi 2, 40126, Bologna, Italy.
O
- [Au+]
R1
R2
R1
1’
O
O
R1
O
b
Departamento de Química Orgánica, Universidade de Vigo, AS Lagoas
1
H
c)
2
(Marcosende) s/n, 36310 Vigo, Spain.
c CITACA - Clúster de Investigación y Transferencia Agroalimentaria del Campus
Auga, Universidad de Vigo, 32004-Ourense, Spain.
d CINMPIS, via Selmi 2, 40126, Bologna, Italy.
Aiming to verify our hypothesis and to get optimal reaction
Supporting Information Placeholder
conditions, an extensive survey of reaction parameters was
carried out by considering the propargylate 1a as a model
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Journal Name
substrate. In Table 1, a summary of tested reaction parameters outcomes have been collected in the Scheme 1. Ketoesters
View Article Online
featuring diversely functionalized aromatDicOrIi:n1g0.s10a3t9t/hDe0CkeCt0o2-7s0i3teK
were adequately tolerated regardless the electronic properties
of the substituents. In details, sterically congested ortho-
substituted arenes (i.e. 2b, 2d and 2k) and the mesitylene
analogous 2e performed satisfyingly too, delivering the
corresponding dioxin-3-one cores in good yields (up to 72%).
is reported (see SI for a complete collection of results).
Delightly, we found out that JohnPhosAuNTf2 (5 mol%)
proved to be the catalyst of election over a series of phosphine
and carbene-based gold complexes (C2-C10). Additionally, the
use of reagent grade xylene at 120 °C and very short reaction
time (50 min) fulfilled the optimal parameters delivering the
dioxinone 2a in high regiochemical manner and 80% yield
(Scheme in Table 1).
Scheme 1. Scope of the reaction. Variations on the -ketoester skeleton (X-ray
structure of 2k is also documented).
Worthy of mentioning, the protocol led almost exclusively
to the six-membered scaffold through the planned O-ring-
closing procedure. On the contrary, the five-membered
counterpart 2a’ was observed in very low amount mainly when
bidendate phosphines were employed (entries 6-9).
a
b
O
O
JohnPhosAuNTf2
(C1, 5 mol%)
c
O
O
a
b
R
O
R
O
c
xylene, 120 °C, 50 min
-
R’
Analogously, NTf2 emerged as the counterion of election
R’
(+/-)-2
1
among the ones tested (entry 1 vs entries 12-14).10 Finally, while
the addition of a base (i.e. KOAc) did not affect significantly the
final outcome of the process (entry 15), an increase in the
2b (X = 2-Me), Y: 60%
2c (X = 4-Me), Y: 58%
2d (X = 2-OMe), Y: 55%
2e (X = 2,4,6-(Me)3), Y: 63%
2f (X = 4-F), Y: 67%
2g (X = 4-Cl), Y: 47%
2h, (X = 4-Br), Y: 64%
2i (X = 2-Br), Y: 80%
O
O
O
O
temperature (entries 16 and 17) led to
a significant
R
O
O
improvement in the isolation of 2a (up to 68% in toluene at 120
°C).
2m, (R = Me), Y: 79%
2n, (R = -C9H19), Y: 57%
2o, (R = -(CH2)2Ph), Y: 55%
X
2j (X = 3-Br,4-F), Y: 80%
2k (X = 2-naphthyl), Y: 72%
2l, (X = 2-benzofuranyl), Y: 72%
Table 1. Optimization of the reaction conditions
O
O
2p, Y: 76%
2k
O
Analogously, when electron-donating (1b-e, 1k and 1l) or
electron-withdrawing (1f-j) units were accommodated at the
aromatic acyclic precursor, excellent catalytic performance
were recorded (yield up to 80%). Linear and cyclic aliphatic
ketones were also synthesized and tested under optimal
conditions (1m-p). Interestingly, no variations on the final
outcome were recorded in all cases (yields: 55-79%).
Then, our focus moved on the applicability of the protocol
towards precursors carrying structural diversity at the
propargylic unit. In this line, a series of acyclic precursors
comprising internal alkynes and branched side chains (1q-u)
were subjected to optimal reaction conditions.
Runa
Deviation from optimal
Yield 2a/2a’
(%)b
80
1
2
3
4
5
6
7
8
9
10
11
12c
13c
14c
15
16
17
--
C1 at 60 °C, toluene
C2 at 60 °C, toluene
C3 at 60 °C, toluene
C4 at 60 °C, toluene
C5 at 60 °C, toluene
C6 at 60 °C, toluene
C7 at 60 °C, toluene
C8 at 60 °C, toluene
C9 at 60 °C, toluene
C10 at 60 °C, toluene
AgSbF6 instead of AgNTf2
AgTFA instead of AgNTf2
AgOTf instead of AgNTf2
with KOAc (2 eq)
50/-
22/-
42/-
40/-
NR
20/19
13/-
-/25
20/-
NR
37/-
NR
37/9
40/-
60/-
68
Scheme 2. Scope of the reaction. Variations on the propargylic chain.
Toluene 100 °C
Toluene 120 °C
a
b
Reaction conditions: 1a (0.2 mmol, 0.05 M), under nitrogen conditions.
Determined after flash chromatography. c The cationic gold complex was obtained
in situ in toluene. NR: no reaction.
Having established the optimal parameters with compound
1a, the generality of the protocol was envisioned by reacting,
under the conditions reported in the Scheme of Table 1, a series
of terminal propargylic derivatives carrying molecular variations
on the -ketoester motif (1b-p). The corresponding chemical
2 | J. Name., 2012, 00, 1-3
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The data collected in Scheme 2 contributed to emphasize
the generality of the method. Here, propargylic carboxylates
deriving from primary and secondary alcohols guaranteed
satisfactory results in the cyclization reactions along with high
stereospecificity for the newly formed C=C bond. Analogously,
the internal alkyne 1t worked satisfyingly in the cascade process
delivering the corresponding dioxin-3-one scaffold 2t in 62%
yield.
Finally, the possibility to apply the present methodology
towards the realization of vinyl-dioxanones was envisioned and
successfully realized by subjecting the carboxylate 1u to optimal
conditions. Satisfyingly, the corresponding vinyl derivative 2u
was obtained in 66% yield and high chemoselective manner.
Prompted by the experimental evidences and intrigued by
COMMUNICATION
Scheme 3. Computed mechanism for the transformation of 1 into 2 and 2a’ at the
View Article Online
PCM(p-Xylene)/M06/def2-SVP theoretical level. Gibbs free energies are reported
DOI: 10.1039/D0CC02703K
in kcal mol−1 (1 atm and 298 K), relative to keto-enol tautomer of 1a. L refers to
PMe3 and X to OTf anion.
X
H
X
H
LAu
O
X
H
TS1
20.0
TS2
20.7
AuL
O
O
O
AuL
O
O
Ph
O
Ph
O
Ph
O
INT0, 12.0
INT1, 6.2
INT2, 11.4
[3,3]-sigmatropic rearrangement
AuL
H
X
AuL
O
Ph
the mostly selective isolation of 2a, we performed
a
O
O
Ph
INT3-A, -0.7
O
computational study on the mechanism governing the trans-
formation of 1a into 2a and 2a’ through DFT. We chose the OTf-
(i.e. X in Scheme 3) anion as counterion as both isomers 2a/2a’
are isolated experimentally when it is present; a summary of the
proposed mechanism is depicted in Scheme 3a (for a full
mechanism see the SI). An analysis of the thermochemical
stability of both alternate products, 2a and 2a’, suggests that
the C-cyclized isomer 2a’, is substantially lower in energy than
the experimentally observed 2a, thereby revealing that the 1a
→ 2a conversion should be kinetically controlled. Initially, the
gold complex coordinates to the alkynyl moiety of the keto-enol
tautomer of 1, which is more stable thermodynamically,
forming intermediate INT0 (+12.0 kcal•mol-1). The subsequent
stepwise [3,3]-sigmatropic rearrangement process towards
INT211 involves a stretched 1,3-dioxane-like gold complex
featuring an allene fragment, INT1. This intermediate is
strikingly more stable than both ends of the sigmatropic process
by about 6 kcal•mol-1. Once INT2 is formed two pathways could
be drawn depending on its O- or C-annulation mode leading
respectively to a 1,3-dioxin-3-one specie INT3-A and to an
unsaturated lactone derivative INT3-B. Computational results
revealed that TS3-A, concerning a simultaneously O-cyclization
and proton trapping by the OTf anion, is +2.9 kcal•mol-1 lower
in energy than the alternative C-cyclized transition state TS3-B.
This energetic difference would be enough to observe product
selectivity (2a vs 2a’). A posterior barrierless protodeauration
process at INT3-A affords the dioxinone derivative 2a (ΔGTS4-A
= -1.6 kcal•mol-1) whereas the similar event at INT3-B¸ to lead
the five-membered isomer 2a’, implies at higher energetic cost
(ΔG≠TS4-B = +13.1 kcal• mol-1).12
On the other hand, deuterium-labeling experiments carried
out on 1a-d3 (see SI for details) revealed a substantial
incorporation of D-atom (51%) at the internal vinyl position (Cb)
of product 2, supporting for the protodeauration of the alkenyl-
gold intermediate INT3-A as the latest stage of the catalytic
cycle. Analogously, the high deuteration content at the acetal
position Cc prompted us to exclude an Au-acetylide mediated
cyclization mechanism (Scheme 3b).13 Partial deuteration of the
Ca-position (ca. 42%) prompted us to consider the participation
of a propargylate/allenoate equilibria of INT0. Our calculations
however revealed that this intermediate is very unstable (18
kcal mol-1) and is therefore unlikely to participate in this
chemistry. Another viable alternative that explain this partial
deuteration is a 1,3-H shift at INT1 (most probably stepwise,
intermolecular and counterion-mediated).
O
O
X
TS4-A, -1.6
XH
H
O
AuL
O
INT4-A, -15.5
Ph
O-Annulation
a)
O
O
Ph
O
1
TS3-A, 20.5
O
LAuX
INT2
2a, -18.6
Ph
O
X
H
O
O
O
O
C-Annulation
HX
Ph
2a', -40.5
INT4-B, -35.1
O
AuL
Ph
O
Ph
O
O
TS3-B, 23.4
O
O
O
INT3-B, -7.8
H
X
LAu
LAu
TS4-B, 5.3
42%
D
51%
b
42%
D
D
D
a
JohnPhosAuNTf2
(5 mol%)
tol-d8, 120 °C, 50 min
86%
O
O
c
O
O
b)
b
a
Ph
O
c
Ph
85%
D
D
O
D
92% d
D
91% d
(+/-)-2-d
(conv.: 95%, NMR)
1-d3
In conclusion,
a
novel gold catalyzed synthetic
methodology for a rapid access to densely functionalized
dioxinones (yield up to 80%) is documented. The protocol
exploits the attitude of homogeneous gold(I) catalysis to assist
multiple and consecutive chemical events (i.e. sigmatropic
rearrangement/nucleophilic trapping of allenes) via site-
selective electrophilic activation of -systems. The high degree
of regioselectivity recorded was corroborated via a detailed
computational investigation that also mapped all key
intermediates of the dual gold activation mode exerted during
the catalytic cycle.
Conflicts of interest
There are no conflicts to declare.
Notes and references
The Supporting Information is available free of charge on the ACS
Publications website. Experimental procedures and analytical
characterization of unknown compounds (PDF); NMR-Spectra
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
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(PDF); Computational data and Cartesian coordinates (PDF); CIF
file for 2k X-ray (.cif)
(p) K. L. Mendhekar, T. R. Pradhan, D. K. Mohapatra, J. Org.
View Article Online
Chem., 2020, 85, 4881.
4
For
a
Pd-catalyzed complementaryDOaI:p1p0r.1o0a3c9h/D0tCoC0v27in0y3lK-
dioxanones see: Y. Ogiwara, K. Sato, N. Sakai, Org. Lett., 2017,
19, 5296. See also: D. C. Elliott, T. K. Ma, A. Selmani, R.
Cookson, Parsons, A. G. M. Barret, Org. Lett., 2016, 18, 1800.
L. Liu, Y. Han, J. Xiao, L. Li, L. Guo, X. Jiang, L. Kong, Y. Che, J.
Nat. Prod., 2016, 79, 2616.
AUTHOR INFORMATION
Corresponding Author
* MB: marco.bandini@unibo.it.
5
6
* CSL: carlos.silva@uvigo.es
Present Addresses:
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Commun., 2011, 47, 7803; (b) G. Cera, S. Piscitelli, M.
Chiarucci, G. Fabrizi, A. Goggiamani, R. S. Ramón, S. P. Nolan,
M. Bandini, Angew. Chem. In. Ed., 2012, 51, 9891; (c) G. Cera,
M. Chiarucci, A. Mazzanti, M. Mancinelli, M. Bandini, Org.
Lett., 2012, 14, 1350; (d) M. Chiarucci, R. Mocci, L. D.
Syntrivanis, G. Cera, A. Mazzanti, M. Bandini, Angew. Chem.
Int. Ed., 2013, 52, 10850; (e) M. Chiarucci, E. Matteucci, G.
Cera, G. Fabrizi, M. Bandini, Chem. Asian J., 2013, 8, 1776; (f)
G. Cera, M. Chiarucci, F. Dosi, M. Bandini, Adv. Synth. Catal.,
2013, 355, 2227; (g) P. Giacinto, G. Cera, A. Bottoni, M.
Bandini, G. P. Miscione, ChemCatChem, 2015, 7, 2480; (h)
M.M. Mastandrea, N. Mellonei, P. Giacinto, A. Collado, S. P.
Nolan, G. P. Miscione, A. Bottoni, M. Bandini, Angew. Chem.
Int. Ed., 2015, 54, 14885; (i) E. Manoni, M. Daka, M. M.
Mastandrea, A. De Nisi, M. Monari, M. Bandini, Adv. Synth.
Catal., 2016, 358, 1404; (l) A. De Nisi, C. Bergamini, M.
Leonzio, G. Sartor, R. Fato, M. Monari, N. Calonghi, M.
Bandini, Dalton Transactions, 2016, 45, 1546; (m) M. Bandini,
G. Cera, G. P. Miscione, ChemCatChem, 2017, 9, 316; (n) J. An,
A. Parodi, M. Monari, M. Castiñeira Reis, C. Silva Lopez, M.
Bandini, Chem. Eur. J., 2017, 23, 2442.
For general review see: (a) M. E. Muratore, A. Homs, C.
Obradors, A. M. Echavarren, Chem. Asian J., 2014, 9, 3066; (b)
R. Dorel, A. M. Echavarren, Chem. Rev., 2015, 115, 9028; (c)
W. Debrouwer, T. S. A. Heugebaert, B. I. Roman, C. V. Stevens,
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(a) N. Marion, S.P. Nolan, Angew. Chem. Int. Ed., 2007, 46,
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† J.A. Institute of Chemical Research of Catalonia (ICIQ), The
Barcelona Institute of Science and Technology, Av. Països
Catalans 16, 43007 Tarragona, Spain.
MM-L: Departamento de Química Orgánica, Facultad de Química,
Regional Campus of International Excellence ‘‘Campus Mare
Nostrum’’, Universidad de Murcia, Murcia-30100, Spain.
ACKNOWLEDGMENT
7
J.A. is grateful to CSC Programme No. 201608310110. University
of Bologna is acknowledged for financial support. C.S.L and M.M.
are grateful to CESGA for allocation of HPC resources and to
MICINN (CTQ2016-75023-C2-2-P) and Xunta de Galicia (ED431E
2018/07) for funding.
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10 For general reviews on the topic see: (a) M. Jia, M. Bandini,
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11 The selective formation of the dioxinone 2t, featuring a
quaternary stereogenic center, supports the initial gold
catalyzed [3,3]-sigmatropic event.
12 Protodeauration barriers, showing
a strong substrate
dependency, can range from kinetically irrelevant to rate
limiting steps. See for instance (a) R. B. Ahmadi, P. Ghanbari,
N.A. Rajabi, A.S.K. Hashmi, B. F. Yates, A. Ariafard.,
Organometallics, 2015, 34, 3186; (b) I. Stylyanakis, O. N. Faza,
O.; C. S. Lopez, A. Kolocouris A., Org. Chem. Front. Org. Chem.
Front. 2020, 7, 997.
13 The presence of adventitious traces of water in the reaction
media could address for the partial loss of deauration content
in 2a-d.
4 | J. Name., 2012, 00, 1-3
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