Reactions of adamantanethione with ketenes: Formation of a 1,3,5-dioxathiane

Article abstract of DOI:10.1071/CH13449

The reaction between adamantanethione 1 and diphenylketene 9 yields 2,4-bis(diphenylmethylidene)-1,3,5-dioxathiane 14 via ketene-thione zwitterions. This is the first example of the formation of a 1,3,5-dioxathiane in a ketene reaction. CSIRO 2014.

Full text of DOI:10.1071/CH13449

RESEARCH FRONT
CSIRO PUBLISHING
Aust. J. Chem. 2014, 67, 525–527
Communication
http://dx.doi.org/10.1071/CH13449
Reactions of Adamantanethione with Ketenes:
Formation of a 1,3,5-Dioxathiane
A
A B
,
Nicholas Drinnan and Curt Wentrup
A
School of Chemistry and Molecular Biosciences, The University of Queensland,
Brisbane, Qld 4072, Australia.
B
Corresponding author. Email: wentrup@uq.edu.au
The reaction between adamantanethione 1 and diphenylketene 9 yields 2,4-bis(diphenylmethylidene)-1,3,5-dioxathiane 14
via ketene–thione zwitterions. This is the first example of the formation of a 1,3,5-dioxathiane in a ketene reaction.
Manuscript received: 28 August 2013.
Manuscript accepted: 17 September 2013.
Published online: 01 October 2013.
Recent interest in zwitterionic intermediates in reactions of
thioketones with diazo compounds, ketenes, and related com-
pounds[1] prompts us to report an unusual reaction of ada-
mantanethione with diphenylketene. A few examples of [2þ2]
cycloaddition of ketenes to thioketones have been reported,[2]
including the addition of the highly reactive and unstable
8-oxoheptafulvene 2 to adamantanethione 1 yielding the
thietan-2-one 3 (Scheme 1).[3] A formal [2þ8] cycloaddition
product 5 is also formed in this reaction, possibly via a zwit-
terionic intermediate 4. An analogous [2þ8] cycloaddition
product is formed from thiotropone and diphenylketene.[4] The
intramolecular, electrocyclic, [2þ2] addition of the ketene
function to the C¼S bond in benzoyl(thiobenzoyl)ketene 6 to
form the corresponding thiet-2-one 7 and similar reactions of
other a-thioxoketenes have also been described (Scheme 2).[5]
Some years ago we reported the first example of [2þ4]
cycloaddition of an a–oxoketene to a thione, viz. the reac-
tion between dipivaloylketene 8 and adamantanethione 1
(Scheme 3).[6] More recently, competing cycloadditions of
thiobenzophenone with benzoyl(phenyl)diazomethane (aziben-
zil), and with benzoyl(phenyl)ketene formed from it by Wolff
rearrangement, have been reported.[7] Conversely, [2þ4]
cycloadditions of ketenes to a,b-unsaturated thioketones[8]
and to N-thioacylimines[9] are also known. Further chemistry
of adamantanethione has been summarised.[10]
Here we report the reaction between adamantanethione 1 and
diphenylketene 9, which we had expected to result in a [2þ2]
cycloaddition to produce a spirocyclic thietanone 10 or oxathie-
tane 11 (Scheme 4). However, neither of these compounds
was isolable. Instead two molecules of the ketene reacted with
one molecule of adamantanethione to produce a compound
C38H34SO2 (m/z 554) as the only discrete isolable product. This
compound could have either of the structures 14, 15, or 16
(Scheme 4). However, structures 15 and 16 are ruled out because
no carbonyl group is indicated in the 13C NMR or in the infrared
(IR) spectrum. The highest chemical shifts are 141 and 149 ppm,
and the highest IR frequencies (other than C–H stretches) are at
1663 and 1597 cmꢀ1, which can be ascribed to aromatic C¼C
stretching. The compound was identified as 14 thanks to a full
assignment of all carbon signals by means of a distortionless
enhancement by polarisation transfer (DEPT)-135 experiment
and an off-resonance decoupled 13C NMR spectrum. There are
27 carbon resonances in all, including three methylene and three
methine signals belonging to the adamantyl unit (demonstrating
that the molecule has a plane of symmetry), 12 CH groups
arising from the four phenyl groups, and four phenyl-ipso
O
S
O
C
S
3
ϩ
ϩ
O
OϪ
S
S
1
2
5
4
Scheme 1. [2þ2] and [2þ8] Cycloadditions of adamantanethione 1 with
the transient 8-oxoheptafulvene 2.
O
O
O
O
S
S
O
C
O
O
O
ϩ
Ph
Ph
Ph
O
C
O
S
Ph
1
8
S
6
7
Scheme 3. [2þ4] Cycloaddition of adamantanethione
dipivaloylketene 8.
1
with
Scheme 2. Electrocyclic formation of 3-benzoyl-4-phenylthiet-2-one 7.
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526
N. Drinnan and C. Wentrup
Ph
in Scheme 4 more likely. We have shown previously that
ketenes form zwitterions with tertiary amines including
pyridines, with very low activation barriers (so-called ketene–
pyridine zwitterions).[11] The present work indicates that
ketene–thione zwitterions are also formed readily.
O
S
S
Ph
O
Ph
Ph
10
11
O
In conclusion, the reaction between adamantanethione 1 and
diphenylketene 9 yields 2,4-bis(diphenylmethylidene)-1,3,5-
dioxathiane 14 via ketene–thione zwitterions. To the best of
our knowledge, this is the first example of the formation of a
1,3,5-dioxathiane in a ketene reaction.
Ph
Ph
C
Ϫ
ϩ
O
S
S
Ph
Ph
ϩ
O
C
Ph
Ph
1
9
12
Experimental
Adamantanethione 1[12] and diphenylketene 9[13] were prepared
according to literature procedures.
Ph
Ph
Ph
Ϫ
O
2,4-Bis(diphenylmethylidene)-1,3,5-dioxathiane 14
Ph
ϩ
O5 3O
A mixture of adamantanethione 1 (0.34 g, 2.0 mmol) and
diphenylketene 9 (0.37 g, 1.9 mmol), together with a crystal of
hydroquinone to inhibit polymerisation, was placed in a flask
under nitrogen for 72 h at room temperature. The contents of the
flask first liquefied to form an orange oil, then after ,40 h
started to solidify as white crystals. The reaction mixture was
extracted several times with hexane, and the combined extracts
were concentrated under vacuum to give a crude yield of 0.48 g
of an off-white crystalline solid. IR spectroscopy demons-
trated that this material was largely identical with the product
purified by chromatography as described below. Column
chromatography on silica gel 60, eluting with CH2Cl2/hexane 3 /
97 afforded 14 as white needles (0.23 g, 44 % based on diphe-
nylketene), mp 176–1788C. (Found: C 81.97, H 6.15. Anal.
Calc. for C38H34SO2: C 82.28, H 6.18 %). dH (CDCl3) 7.45–6.92
(m, 20H), 2.42–1.47 (m, 14H); dC (CDCl3): assignment as C (not
carrying any protons), CH or CH2 on the basis of DEPT-
135 spectrum; multiplicity in the H-coupled spectrum given,
s ¼ singlet, d ¼ doublet (CH), t ¼ triplet, m ¼ multiplet: 148.9
(C, s), 140.9 (C, s), 139.6 (C, t), 138.6 (C, t), 138.3 (C, t), 137.6
(C, t), 130.7 (CH, d), 130.5 (CH, d), 130.4 (CH, d), 129.3
(CH, d), 128.2 (CH, d), 127.8 (CH, d), 127.7 (CH, d), 127.5
(CH, d), 127.2 (CH, d), 126.3 (CH, d), 126.1 (CH, d), 126.0
(CH, d), 124.4 (C, m), 106.3 (C, m), 97.7 (C, m), 38.5 (CH, d),
37.6 (CH2, t), 34.5 (CH2, t), 32.7 (CH2, t), 26.6 (CH, d), 26.2
(CH, d); m/z (EI, 70 eV) 554 (Mþ.), 360 ([M–Ph2CCO]þ.),
332 ([M–PH2CCO–CO]þ.), 300 ([M–Ph2CCO–COS]þ.),
210 ([Ph2CCS]þ.), 194 ([Ph2CCO]þ.), 166 (1þ.), 165, 134
(adamantylideneþ.), 77 (Phþ.); nmax (KBr)/cmꢀ1 3054–2856,
1663, 1597, 1496, 1443, 1120, 1197, 1108.
O
S
1
S
Ph
Ph
Ph
Ph
14
13
Ph
Ph
O
Ph
Ph
Ph
Ph
Ph
Ph
O
S
S
O
O
15
16
Scheme 4. Formation of 1,3,5-dioxathiane 14.
carbons, the latter appearing as triplets in the proton-coupled
spectrum (thus, all four phenyl groups are magnetically differ-
ent). Other signals for carbons not carrying directly attached
protons at 98, 106, and 124 ppm can be identified as the
diphenylvinyl and spiro (C6 in the dioxathiane ring) carbons,
because they become multiplets in the proton-coupled spectrum
due to long-range C–H couplings. Two remaining vinyl-type
carbons at 141 and 149 ppm, which remain singletsin the proton-
coupled spectrum, are assigned to C2 and C4 in the dioxathiane
ring in 14.
The mass spectrum is also in good agreement with structure
14. Important fragment peaks at m/z 166, 194, and 210 indicate
cycloreversion reactions to form the molecular ions of adamanta-
nethione, diphenylketene, and diphenylthioketene, respectively.
A logical mechanism for the formation of 14 involves the
initial formation of a zwitterion 12 (Scheme 4) by nucleophilic
attack of the thione on the ketene C¼O group. Rather than
cyclising to either 10 or 11, the zwitterion is sufficiently long-
lived to add to another molecule of diphenylketene, giving a new
zwitterion 13. Cyclisation of the latter affords the final product.
One may ask why a mono-addition product 10 or 11 is not
formed in this case, when it is formed in the reaction shown in
Scheme 1. A likely reason is that ketene 2 is very short-lived and
has to be generated in situ. Hence the concentration of 2 will
never build up sufficiently for a double addition. In contrast,
diphenylketene is a relatively stable compound, which is avail-
able in excess from the beginning of the reaction. A concerted
three-component [2þ2þ2] cycloaddition is of course also
imaginable but entropically unlikely. The ubiquitous formation
of sulfur-based zwitterions[1] makes the stepwise process shown
Acknowledgement
This work was supported by the Australian Research Council and The
University of Queensland.
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