New reactions of allenes, alkynes, ynamides, enynones and isothiocyanates

Article abstract of DOI:10.1007/s12039-018-1496-2

Abstract: This perspective article is related to transformations (both catalytic and non-catalytic) involving allenes, alkynes/enynones/ynamides and isothiocyanates. Part of the work from the author’s group has been reviewed along with some new reactions of (i) allenylphosphonate/allenylphosphine oxide and (ii) a P(III) isothiocyanate. Thus, the allenylphosphine oxide Ph ₂P(O)C(Ph)=C=CH ₂ undergoes base (DBU) catalyzed addition to the β-ketophosphonate (OCH ₂CMe ₂CH ₂O)P(O)CH ₂C(O)CH ₃ at 90°C to afford the addition product Ph ₂P(O)C(Ph)=C(Me)CH[C(O)Me][P(O)(OCH ₂CMe ₂CH ₂O)]. In an analogous reaction, with DBU as the base at 140°C, isomeric vinylphosphine oxides (Z)-Ph ₂P(O)C(Ph)=C(Me)CH ₂[C(O)Me] and (E)-Ph ₂P(O)C(Ph)=C(Me)CH ₂[C(O)Me] were isolated. The E-isomer has been characterized by single crystal X-ray structure determination. In another set of studies, the reaction of P(III) isothiocyanate (OCH ₂CMe ₂CH ₂O)P(NCS) with N-(2-bromomethyl)sulfonamide afforded an unusual product with the formula (OCH ₂CMe ₂CH ₂O)P(O)SCH ₂CH ₂NHS(O) ₂-(C ₆H ₄-4-Me) as shown by X-ray structure determination. This result is different from that obtained in the recently reported analogous reaction using phenyl isothiocyanate. Graphical Abstract: Synopsis. Base-catalyzed the addition of β-ketophosphonate or ethyl acetoacetate to allenylphosphine oxide affords vinylphosphine oxides; in the latter case, elimination of the ester group also takes place. It is also shown that reactivity of a P(III) isothiocyanate is different from that of organic isothiocyanates. [Figure not available: see fulltext.].

Full text of DOI:10.1007/s12039-018-1496-2

J. Chem. Sci. (2018) 130:99
© Indian Academy of Sciences
https://doi.org/10.1007/s12039-018-1496-2
PERSPECTIVE ARTICLE
Special Issue on Modern Trends in Inorganic Chemistry
New reactions of allenes, alkynes, ynamides, enynones and
isothiocyanates
K C KUMARA SWAMY∗ , G GANGADHARARAO, MANDALA ANITHA,
A LEELA SIVAKUMARI, ALLA SIVA REDDY, ADULA KALYANI and
SRINIVASARAO ALLU
School of Chemistry, University of Hyderabad, Hyderabad, Telangana 500 046, India
E-mail: kckssc@uohyd.ac.in; kckssc@yahoo.com
MS received 7 April 2018; revised 19 May 2018; accepted 25 May 2018; published online 13 July 2018
Abstract. This perspective article is related to transformations (both catalytic and non-catalytic) involving
allenes, alkynes/enynones/ynamides and isothiocyanates. Part of the work from the author’s group has
been reviewed along with some new reactions of (i) allenylphosphonate/allenylphosphine oxide and (ii)
a P(III) isothiocyanate. Thus, the allenylphosphine oxide Ph2P(O)C(Ph)=C=CH2 undergoes base (DBU)
catalyzed addition to the β-ketophosphonate (OCH2CMe2CH2O)P(O)CH2C(O)CH3 at 90 ◦C to afford the
addition product Ph2P(O)C(Ph)=C(Me)CH[C(O)Me][P(O)(OCH2CMe2CH2O)]. In an analogous reaction,
with DBU as the base at 140 ◦C, isomeric vinylphosphine oxides (Z)-Ph2P(O)C(Ph)=C(Me)CH2[C(O)Me]
and (E)-Ph2P(O)C(Ph)=C(Me)CH2[C(O)Me] were isolated. The E-isomer has been characterized by single
crystal X-ray structure determination. In another set of studies, the reaction of P(III) isothiocyanate
(OCH2CMe2CH2O)P(NCS)with N-(2-bromomethyl)sulfonamideaffordedanunusualproductwiththeformula
(OCH2CMe2CH2O)P(O)SCH2CH2NHS(O)2-(C6H4-4-Me) as shown by X-ray structure determination. This
result is different from that obtained in the recently reported analogous reaction using phenyl isothiocyanate.
Keywords. Allene; allenylphosphine oxide; enynone; ynamide; P(III) isothiocyanate; X-ray structure.
1. Introduction
central carbon that is sp-hybridized and amenable for
nucleophilic attack.5 The unsaturated systems such as
these are also useful in diverse catalytic transforma-
tions. Some aspects of reactions of these substrates from
our research group will be highlighted in this short
paper.
The enormous reactivity of organic substrates possess-
ing sp-hybridized carbon, as in alkynes or allenes, has
led to numerous synthetic methodologies.1 In many
reactions involving alkynes, allenic intermediates have
been proposed or isolated and in some cases this
feature has been utilized as a synthetic route to spe-
cific class of allenes (cf. Figure 1).1,2 Ynamides are
also a special type of alkynes in which the reac-
tivity may depend on the ketenimium species that
are analogous to allenes.3 Another class of alkynes,
2. Experimental
Solvents were dried according to known methods as
appropriate.6 1H, 13C and 31P NMR spectra (1H-400 MHz
or 500 MHz, 13C-100 MHz or 125 MHz and 31P-162 MHz)
the enynones/enynals, also have reactivity that are were recorded using a 400 MHz or 500 MHz spectrometer
in CDCl3 (unless stated otherwise) with shifts referenced to
SiMe4 (δ = 0). IR spectra were recorded on an FTIR spec-
trophotometer. Melting points were determined by using a
local hot-stage melting point apparatus and are uncorrected.
High-resolution mass spectra (HR-MS) were performed using
a BRUKER-MAXIS mass spectrometer with ESI-QTOF-II
method.
typical of normal alkynes but can show additional
features because of the conjugated system.4 Perhaps
more interesting correlation is to a system like that of
isothiocyanates (or isocyanates/CO2/CS2) that have a
*
For correspondence
Electronic supplementary material: The online version of this article (https://doi.org/10.1007/s12039-018-1496-2) contains
supplementary material, which is available to authorized users.
1

99 Page 2 of 11
J. Chem. Sci. (2018) 130:99
2.2 Synthesis of (E)-3-(5,5-dimethyl-2-oxido-1,3,2-
dioxaphosphinan-2-yl-5 (diphenylphosphoryl)-
4-methyl-5-phenylpent-4-en-2-one (23)(Scheme 6)
To an oven dried Schlenk tube, ketone 19 (0.17 g, 0.80 mmol),
allene 22 (0.25 g, 0.80 mmol) and DBU (0.025 g, 0.16 mmol)
in dry DMSO (5 mL) were added. The contents were sealed
under nitrogen atmosphere and stirred at 90 ◦C (oil bath tem-
perature) for 8 h. The work up and isolation of the compound
were similar to that given above using hexane-ethyl acetate
(7:3) as the eluent to afford (E)-3-(5,5-dimethyl-2-oxido-
1,3,2-dioxaphosphinan-2-yl-5(diphenylphosphoryl)-4-meth-
yl-5-phenylpent-4-en-2-one (23). Compound 23: Yield:
0.250 g (60%); gummy liquid ∼95% purity ; IR (KBr): 3063,
2973, 2926, 1717, 1481, 1420, 1370, 1285, 1117, 1057, 1013,
791, 756, 725, 700 cm−1 1H NMR (400MHz, CDCl3)δ
;
Figure 1. Some reactive species possessing central
sp-hybridized carbon.
7.68–7.63 (m, 2H), 7.48–7.32 (m, 4H), 7.26–7.21 (m, 4H),
7.14–7.01 (m, 7H), 6.99–6.79 (m, 3H), 6.39 (d, J = 6.8 Hz,
1H), 4.88–4.82 (m, 2H), 4.02–3.84 (m, 2H), 2.14 (s, 3H),
1.92 (s, 3H), 1.19 (s, 3H), 1.02 (s, 3H); 13C NMR (100MHz,
CDCl3)δ 200.0, 151.2, 137.5 (J = 11.6 Hz), 133.3, 132.2,
131.9 (J = 10.4 Hz), 131.6 (J = 10.4 Hz), 131.5, 130.6
(J = 106.5 Hz, P − C), 130.3, 129.4, 128.9, 128.8, 128.4,
128.2, 127.7, 127.6, 127.1, 122.8, 93.9, 82.0,77.2 (d, J =
8.7 Hz), 65.5, 56.7 (J = 109.1 Hz, P-C), 32.8 (J = 7.2 Hz),
2.1 Synthesis of (E)-3,5-bis(5,5-dimethyl-2-oxido-
1,3,2-dioxaphosphinan-2-yl)-4-methyl-5-phenylpent-
4-en-2-one (21) (Scheme 6)
1
31.5, 30.4, 29.7, 22.3 (J = 11.4 Hz), 22.2, 20.4., 31P{ H}
To an oven dried Schlenk tube, ketone 19 (0.35 g, 1.70 mmol),
allenylphosphonate 20 (0.45 g, 1.70 mmol), K2CO3(0.047 g,
0.341 mmol) and dry DMSO (5 mL) were added. The con-
tents were sealed under nitrogen atmosphere and stirred at
90 ◦C (oil bath temperature) for 8 h. After completion of
the reaction as monitored by TLC, the crude reaction mix-
ture was cooled to 25 ◦C, diluted with ethyl acetate (20 mL)
and washed with water. The organic layer was washed with
brine solution, dried over anhyd. Na2SO4 and concentrated
NMR (162 MHz, CDCl3) δ 31.7 (d, J = 4.1 Hz), 12.3
(d, J = 4.1 Hz); LC/MS m/z 471 [M+ +H]. HRMS (ESI):
Calcd. for C29H33O5P2 [ M++H]: m/z 523.1804. Found:
523.1804
2.3 Synthesis of (Z)-5-(diphenylphosphoryl)-4-
methyl-5-phenylpent-4-en-2-one (24) and (E)-5-
under vacuum. The residue was purified by using silica (diphenylphosphoryl)-4-methyl-5- phenylpent-4-en-2-
gel column chromatography with hexane-ethyl acetate (3:7)
as the eluent to afford (E)-3,5-bis(5,5-dimethyl-2-oxido-
one (25) (Scheme 6)
1,3,2-dioxaphosphinan-2-yl)-4-methyl-5-phenylpent-4-en-2- To an oven dried Schlenk tube, allene 22 (0.50 g, 1.58 mmol),
one (21). Compound 21: Yield: 0.309 g (68%); gummy liquid; ethyl acetoacetate (0.31 g, 2.37 mmol), DBU (0.048 g, 0.31
IR (KBr): 3057, 2973, 2886, 1809, 1715, 1605, 1472, 1373, mmol), DMSO (5 mL) were added. The contents were sealed
1
1283, 1071, 916, 829, 735, 704, 635 cm−1; H NMR (400 under nitrogen atmosphere and heated with stirring at 140 ◦C
MHz, CDCl3)δ 7.38–7.27 (m, 3H), 7.19 (br m, 2H), 6.38 (oil bath temperature) for 6 h. The work up was similar to
(d, J = 24.8 Hz, 1H), 4.62 (d, J = 11.2 Hz, 1H), 4.53 above and the compounds (Z)−5-(diphenylphosphoryl)-4-
(d, J = 11.2 Hz, 1H), 3.97–3.82 (m, 4H), 3.62 (t, J = methyl-5-phenylpent-4-en-2-one (24; higher Rf) and (E)-
12.0 Hz, 1H), 3.32 (t, J = 13.4 Hz, 1H), 2.41 (s, 3H), 5-(diphenylphosphoryl)-4-methyl-5-phenylpent-4-en-2-one
1.91 (s, 3H), 1.30 (s, 3H), 0.95 (s, 6H), 0.52 (s, 3H); 13C (25; lower Rf) were isolated using hexane-ethyl acetate
NMR (100 MHz, CDCl3)δ 199.3, 151.6 (J = 10.4, 5.5 Hz), (4:6) as the eluent. Compound 24: Yield: 0.172 g (29%,
136.6 (J = 9.0 Hz), 130.8 (J = 164.9, 12.1 Hz, P − C), purity >95%); gummy liquid; IR (KBr): 3057, 2922, 1715,
130.0 129.8, 128.6, 127.8, 76.1 (J = 6.4 Hz), 75.8 (J = 1678, 1609, 1487, 1437, 1358, 1316, 1173, 1115, 1026,
6.1 Hz), 57.4 (J = 6.3 Hz), 56.2 (J = 6.3 Hz), 56.8 754 cm−1; 1H NMR (400 MHz, CDCl3)δ 7.57–7.52 (m, 5H),
(J = 117.5, 6.3 Hz, P − C), 32.6 (J = 7.2 Hz), 32.3 7.40–7.38 (m, 2H), 7.32–7.27 (m, 5H), 7.04–7.02 (m, 3H),
(J = 6.6 Hz), 30.3, 22.1, 21.7, 21.2 (J = 16.4 Hz), 20.7, 6.79–6.77 (m, 2H), 4.18 (s, 2H), 2.04 (s, 3H), 1.73 (s, 3H);
1
20.4; 31P{ H}NMR(162 MHz, CDCl3)δ 11.7 (J = 6.0 Hz), 13C NMR (100 MHz, CDCl3)δ 205.7, 151.8 (J = 6.1 Hz),
10.7 (J = 5.8 Hz); LC/MS: m/z 471 [M+ +H]; Anal. 138.2 (J = 11.2 Hz), 132.8 (J = 103.0 Hz, P-C), 131.7,
Calcd. C22H32O7P2: C, 56.17; H, 6.86%; Found: C, 56.31, 131.6, 131.3, 131.2, 131.0, 130.11, 130.07, 128.5, 128.1,
H, 6.81%. HRMS (ESI): Calcd. for C22H33O7P2[M+ +H]: 127.9, 126.7, 50.1 (J = 6.8 Hz), 30.1, 24.2 (J = 11.5 Hz);
1
m/z 471.1702. Found: 471.1703.
31P{ H} NMR (162 MHz, CDCl3)δ 28.9; LC/MS m/z 375

J. Chem. Sci. (2018) 130:99
Page 3 of 11 99
[M+ +H]. HRMS (ESI): Calcd. for C24H24O2P [ M+ +H]: was only moderate, but the refinement could be satisfactorily
m/z 375.1515. Found: 375.1515.
done. CCDC no. 1575674.
Compound 25: Yield: 0.207 g (35%); white solid, M.p.:
172–176 ◦C; IR (KBr): 3048, 2924, 1715, 1678, 1609, 1478,
1437, 1358, 1315, 1173, 1115, 1026, 754 cm−1; H NMR
1
3. Results and Discussion
(400 MHz, CDCl3)δ 7.66–7.61 (m, 4H), 7.40–7.38 (m, 2H),
7.32–7.27 (m, 4H), 6.99–6.96 (m, 3H), 6.80 (d, J = 6.8 Hz,
2H), 3.19 (s, 2H), 2.25 (d, J = 2.8 Hz, 3H), 2.01 (s, 3H);
13C NMR (100 MHz, CDCl3)δ 205.6, 151.0 (J = 7.8 Hz),
134.4, 133.4, 133.3 (J = 103.0 Hz, P-C), 132.0, 131.9,
131.3, 129.4, 128.2, 128.1, 126.9, 52.6 (J = 11.6 Hz),
3.1 Reactivity of allenylphosphonates/allenyl-
phosphine oxides
Selected reactions of allenylphosphonates/allenylphos-
phine oxides reported from our laboratory are shown
in Scheme 1.8 Many of these have been summarized
1
30.3, 23.0 (J = 7.5 Hz); 31P{ H} NMR (162 MHz, CDCl3)δ
29.2; LC/MS m/z 375 [M+ +H]; Anal. Calcd. C24H23O2P:
C, 76.99; H, 6.19%; Found: C, 77.1, H, 6.15%. HRMS (ESI): in a recent article.8a While performing these reactions
Calcd. for C24H24O2P [ M++H]: m/z 375.1515. Found:
we were also curious to see whether some intermedi-
ates can be isolated. For example, in the reaction shown
375.1517.
in Scheme 2a, two equivalents of the thiophosphite
2.4 Synthesis of N-(2-((5,5-Dimethyl-2-oxido-1,3,2-
dioxaphosphinan-2-yl)thio)ethyl)-4-methylbenzene
sulfonamide (48) (Scheme 13)
(OCH2CMe2CH2O)P(S)H (2) can be added (cf. com-
pound 5) on to the allene 1 in the presence of Pd(PPh3)4,
but in a blank reaction in the absence of allene, we could
isolate the [Pd] species 6 (Scheme 2b). Interestingly, this
compound 6 was also very effective in catalyzing the
same phosphonylation reaction.8b
N-(2-Bromoethyl) sulfonamide 45 (0.36 mmol) and 3-
((isothiocyanato(methyl)phosphino)oxy)-2,2-dimethylprop-
an-1-ol 47 (0.54 mmol) were used. Yield 0.118 g (86%,
In another study, we were investigating the phospho-
nylation reactions of allenylphosphonates and Baylis-
Hillman adducts using tetrabutylammonium fluoride
[(n-Bu)4NF] as the catalyst in ionic liquid [bmim]+
[PF6]− as the medium (Scheme 3).9 It is impor-
◦
white solid); M.p.: 136–138 C; IR (KBr)νmax 3175, 2974,
1324, 1262, 1155, 1092, 1050, 1000, 835, 782, 732 cm−1
;
1H NMR (400 MHz, CDCl3) δ 7.71–7.69 (m, 2H), 7.24
(d, J 8.0 Hz, 2H), 6.19 (br, 1H), 4.08 (d, J
12.0 Hz, 2H), 3.90–3.83 (m, 2H), 3.20–3.18 (m, 2H), 2.95–
=
=
2.92 (m, 2H), 2.36 (s, 3H), 1.21 (s, 3H), 0.83 (s, 3H); tant to note that pentacoordinate phosphorus inter-
13C NMR (100 MHz, CDCl3) δ 143.2, 137.1, 129.7, 127.0,
mediates are proposed in numerous reactions involv-
ing tetracoordinate phosphorus. However, they have
been rarely been identified spectroscopically. In the
78.1 (J = 5.5 Hz), 43.6 (J = 2.1 Hz), 32.4 (J =
6.0 Hz), 29.4, 21.8, 21.4, 20.2; 31P NMR (162 MHz, CDCl3)
δ 20.74; HRMS (ESI) calcd. for C14H22NO5PS2Na(M++Na)
present case, we have been able to elegantly iden-
402.0575, found: 402.0575. This compound was crystal-
tify such an intermediate [Scheme 3b; case (ii)] by
lized from dichloromethane/ethyl acetate (2:1) mixture at
1
the combined use of 31P, H and 19F NMR spec-
25 ◦C.
troscopy wherein the values of 1 JPF [959.5 Hz],
2
1 JPH [652.4 Hz] and JFH [129.4 Hz] could be eas-
2.5 X-ray structural analysis of compounds 25 and 48
1
ily discerned.9 The H NMR and 13C NMR spectra
were also consistent with the phosphocin ring being
intact.
In another interesting reaction of allenes wherein both
solved by direct methods and refined by full-matrix least phosphine and gold catalysis is involved, we chose an
Single crystal X-ray data for compounds 25 and 48 were col-
lected on a Bruker AXS-SMART or OXFORD diffractometer
using Mo-K ( = 0.71073Å) radiation. The structures were
λ
α
squares method using standard procedures.7
allenoate10. Thus, inaone-potreaction, theallenoate10
Compound 25: C24H23O2P, M = 374.39, monoclinic,
space group P21/n, a = 11.9638(7)Å, b = 10.6625(5)Å,
c = 16.0875(8)Å, β = 93.956(5)◦, V = 2047.30(17)Å3, Z
= 4, μ=0.150 mm−1, data/restraints/parameters 3598/0/246,
reacted with the enynal 11 to afford trisubstituted benzo-
furan13viacyclopenteneintermediate12(Scheme4).10
For the first step in the formation of the cyclopentenes
12, initial attack of the phosphine on the allenoate 10
can be envisaged. However, to date, the exact species
of type 14 has not been characterized. The closest that
we have been able to isolate and structurally character-
ize are the compounds 16’ and 16” using the Inorganic
ring system [(t-BuNH)P[N(t-Bu)]2P(NH-t-Bu)] (15).11
Thus attack of the trivalent phosphorus on the central
σ
R indices (I > 2 (I)) R1 = 0.0454, wR2 (all data) = 0.1145.
CCDC no. 1834021.
Compound 48: C14H22NO5PS2, M = 379.42, triclinic,
space group P-1, a = 6.8296(8)Å, b = 7.4875(8)Å,
c = 18.4067(19)Å, α = 80.149(5), β = 81.744(5), γ =
82.580(4), V = 912.47(17)Å3, Z = 2, μ = 0.440 mm−1
,
data/restraints/parameters 3205/4/214, R indices (I > 2σ(I))
R1 =0.1064, wR2 (all data) = 0.2825. The quality of data sp-hybridized β-carbon of the allene affords 16 which

99 Page 4 of 11
J. Chem. Sci. (2018) 130:99
Scheme 1. Cyclization/cycloaddition reactions of allenylphosphonates/allenylphosphine
oxides. Conditions: (i) K3PO4 (0.5 equiv.), THF, 80 ◦C, 12 h/ NaOH (2 equiv.), EtOH/H2O
(4:1), 80 ◦C, 8 h;8a (ii) K2CO3 (20 mol%), DMSO, 90 ◦C, 4 h;8e (iii) K3PO4 (20 mol%), DMSO,
120 ◦C, 8–12 h;8a (iv) Propargylic alcohols, Zn(OTf)2 (10 mol%), Et3N (20 mol%), toluene,
100 ◦C, 8 h;8c (v) Et2NH, CH3CN, rt (25 ◦C), 8 h;8a (vi) K2CO3 (20 mol%), DMSO, 90 ◦C, 24
h;8e (vii) ZrCl4 (0.5 mol equiv.), MeOH, reflux, 2–3 h;8a .(viii) Me3SiN3, CH3CN, reflux, 18–20
h;8 f (ix) Me3SiN3, DMF/CH3C(O)CH2CO2Et, Mn(OAc)3, MeOH, rt;8a (x) K2CO3 (20 mol%),
PEG-400, 90 ◦C, 4 h.8d.
(a)
(b)
Scheme 2. [Pd]-catalyzed thiophosphonylation of allenylphosphonate 1 and isolation of the catalytically
active intermediate 6.
then rearranges to 16’/16”. Conversion of cyclopentene
12 to the benzofuran 13 is also complex but is assumed ceptible to attack by water and thus (OCH2CMe2CH2O)
to involve the [Au]-intermediates 17/17’ (Scheme 5). P(O)CH=C=CH2 18canbeconvertedtotheβ-ketophos-
Sterically unhindered allenylphosphonates are sus-

J. Chem. Sci. (2018) 130:99
Page 5 of 11 99
(a)
(b)
Scheme 3. The [(n-Bu)4NF] mediated/catalyzed addition of a phosphite to allenylphosphonate showing
the pentacoordinate phosphorus species.
Scheme 4. One pot PPh3 and [Au]-catalyzed reaction of allenoate with enynal for the formation of multiply
substituted benzofuran.
(a)
(b)
(c)
Scheme 5. (a) Possible intermediates in the phosphine catalyzed reaction of allenoate; (b) Isola-
tion of intermediate-type species using cyclodiphosphazane and; (c) Two plausible intermediates
in the [Au] catalyzed reaction of alkyne substituted cyclopentenes.

99 Page 6 of 11
J. Chem. Sci. (2018) 130:99
(a)
(b)
(c)
(d)
Scheme 6. (a) Formation of β-ketophosphonate 19 from allenylphosphonate 18; (b)–(c) reactions
of allenylphosphonate 20 and allenylphosphine oxide 22 with β-ketophosphonate 19 to afford 23; (d)
reaction of allenylphosphine oxide 22 with ethyl acetoacetate to afford 24–25.
phonate (OCH2CMe2CH2O)P(O)CH2C(O)CH3(19)12
in the presence of a base. Since compound 19 can take
part in Horner-Wadsworth reaction, we envisaged that
the anion thus obtained should act as a nucleophile
towards the central sp-hybridized carbon of the allenylp-
hosphonateoftype20. Indeedthisreactiondidoccurand
we could readily isolate the bisphosphonate 21. A sim-
ilar reaction occurred using the allenylphosphine oxide
22 and phosphonate-phosphine oxide 23 was obtained
in decent yields. In the latter case though, we used DBU
as the base. Interestingly, in the reaction of allenylphos-
phine oxide 22 with ethyl acetoacetate, we obtained a
different set of products, the isomeric 24–25 in which
the ester moiety was removed probably via adventitious
moisture present in the system. The X-ray structure of
the E-isomer, 25 has been determined (Figure 2). It is
possible that the olefinic double bond may shift itself to
give enone isomers in these cases. Indeed in the reaction
of22withethylacetoacetateinthepresenceofK2CO3 or
DABCO such isomers appear to form,13 but these reac-
tions need to be studied further in order to get insight
into the mechanistic details as well as utility.
Figure 2. Molecular structure of compound 25
showing the E-configuration. Only selected hydro-
gen atoms are shown. Selected bond distances
(Å) with esds: P1–O1 1.486(1), P1–C7 1.796(2),
P1–C1 1.809(2), P1–C13 1.821(2), C13–C20
1.341(3), C20–C22 1.500(3), C20–C21 1.510(3).
CCDC No. 1834021.
reactions that we investigated is the double arylation
of alkynes.14 Analogous reactions are generally carried
out in the presence of [Pd(PPh3)4] in a nonaqueous sol-
vent.15 Interestingly, we could effect this reaction of the
3.2 Alkyne enynone/enynal/ynamide reactivity
As mentioned above (cf. Figure 1) both alkyne and alkyne 26 on water within a very short time using the
allene have a reactive sp-hybridized carbon. One of the palladium catalyst 6 alluded to before (cf. Scheme 7),

J. Chem. Sci. (2018) 130:99
Page 7 of 11 99
(a)
(b)
Scheme 7. Double arylation of alkyne 26 using our catalyst
6 on water to afford 27.
Scheme 9. [Ru]-catalyzed alkyne insertion onto purine base
appended aniline via C-H activation.
giving rise to the double arylated product 27.14 The
reaction could be readily monitored by 31P NMR spec-
troscopywhichsuggestedthatcatalyst6ismoreefficient
than the traditional [Pd(PPh3)4] and readily afforded
clean products.
In a significant number of reactions involving alkyne
insertion, the ruthenium catalyst [RuCl2(p-cymene)]2 is
used.16 The substrate generally has a directing group
(e.g., 8-aminoquinoline). In reactions such as these,
it is generally assumed that both the chlorines of
[RuCl2(p-cymene)]2 are replaced under catalytic con-
ditions. However, for the annulation reaction shown in
Scheme 8, we found that only one of the chlorines on the
catalyst/pre-catalyst [RuCl2(p-cymene)]2 gets replaced
in the absence of the substrate 28 to afford the complex
[RuCl(OAc)(p-cymene)] (30). What is more interesting
Scheme 10. Gold-catalyzed the formation of triazine fused
furans; the possible intermediates are also shown.
is that this intermediate 30 reacts with N-quinolin-8-yl- this study suggested that there may be other (previously
benzamide 28 to give the ruthenium complex 31 that can not formulated) intermediates for this alkyne insertion
also act as a catalyst for the alkyne insertion.17 Thus, reaction.
(a)
(b)
Scheme 8. (a) Alkyne insertion using the ruthenium catalyst/precatalyst [RuCl2(p-cymene)]2
and (b) isolation of an intermediate type ruthenium complex 31.

99 Page 8 of 11
J. Chem. Sci. (2018) 130:99
the alkynophilic [Au] catalysts is shown in Scheme 10.19
Here, the reaction of azide with the enynone/enynal
under gold catalysis leads to the formation of a 6-
membered triazine ring compound, rather than the
familiar click reaction in which a triazole is obtained.
The main condition for this to happen is that the group
R1 has to be aromatic. Several [Au]-intermediates are
involved in this process; three of them are shown in the
scheme.
(a)
Ynamides belong to a special type of alkynes in which
the reactivity of the two sp-hybridized carbon atoms
of the alkyne exhibit vastly different reactivity.3 One
example in which we could insert elemental sulfur or
selenium directly into the ring system via copper catal-
ysis is demonstrated in Scheme 11a.20 Here, the initial
reaction of CuI with the iodo-substituted ynamide is
assumed to lead to an intermediate in which the copper
is connected to the arene [cf. Scheme 11a). The sulfur
[Sn]2− (or similar selenide) anion is produced from sul-
fur in the presence of the base K2CO3 and water. Perhaps
a more interesting reaction of the ynamide is catalytic
hydrogenation using ethanol as the hydrogenating agent
under palladium catalysis. An example of this is shown
in Scheme 11b.21 Here, the E-enamide is formed pref-
erentially.
(b)
Scheme 11. (a) Sulfur/selenium insertion reaction of
ynamides and; (b) E-selective hydrogenation of ynamides
using ethanol as the hydrogenating agent.
In another alkyne insertion reaction on the sub-
strate 32 leading to the annulated product 33 shown in
Scheme 9, we have used purine as the directing group.18
In a manner similar to that shown in Scheme 8, we
were able to isolate the ruthenium complex 34. Such an
observation suggests that in these reactions [RuCl2(p-
cymene)]2 acts only as a pre-catalyst.
3.3 Isothiocyanate reactivity
Carbon disulfide (S=C=S), as well as aryl isothio-
Enynones/enynals have double bonds, generally in cyanates ArN=C=S, have a central sp-hybridized carbon
conjugation with the alkyne moiety. This structural which is susceptible to nucleophilic attack.5 In this
feature may impart new type of reactivity for such a sub- sense, this system is analogous to the allene system
strate. One such example reported from our group using described above (cf. Figure 1). We have been interested
Scheme 12. Base-mediated reaction of cumulenes (CS2/PhNCS) with epoxy sulfonamides.

J. Chem. Sci. (2018) 130:99
Page 9 of 11 99
(a)
(b)
Scheme 13. (a) Reaction of aryl isothiocyanate 44 with bromoethylsulfonamide 45 to afford 46; (b)
Unusual reaction of bromoethyl-sulfonamide with P(III) isothiocyanate 47 to afford 48.
NMR (1H and 13C) and HRMS data are consistent with
the structure shown below (Scheme 13b). The structure
of compound 48 was also confirmed by X-ray crystal-
lography (Figure 3). More investigations, though, are
needed to rationalize this observation.
4. Conclusions
Figure 3. Molecular structure of compound 48. The data
quality was only moderate in this case. Selected bond Recent work on the reactions of allenylphosphonates/
lengths [Å] with esds in parentheses: N1–C7 1.404(8), C8–C7
1.398(9), S2–C8 1.777(7), P1–S2 2.052(4), P1–O3 1.427(7),
N1–H1 0.751(11), S1–N1 1.583(10). CCDC no. 1575674.
allenylphosphine oxides, alkynes, enynones, ynamides
and isothiocyanates has been summarized. In a new
set of reactions, it is shown that allenylphospho-
nates/allenylphosphine oxides undergo addition reac-
tions with β-ketophosphonate to lead to products in
which the nucleophilic attack at the central sp-hybridi-
zed carbon of the allene is involved. In a slightly differ-
ent pathway, allenylphosphine oxide (e.g., 22) reacted
with ethyl acetoacetate to afford isomeric vinylphos-
phine oxides with the elimination of the ester moiety
in the presence of adventitious moisture. It is also
shown that the reactivity of a P(III) isothiocyanate
is different from the reaction of traditional organic
isothiocyanates.
in extending the chemistry of allenes to include carbon
disulfide or isothiocyanates/isocyanates. An example
from a recent report is shown in Scheme 12.22 In this
case, a nucleophile is generated by the removal of NH
proton from 41 in the presence of the base; this nucle-
ophile attacks the sp-hybridized carbon center of carbon
disulfide or isothiocyanate/isocyanate in a manner anal-
ogous to that with central carbon of allenes. Subsequent
cyclization/epoxide ring opening and the addition of
proton leads to the final products of types 42–43.
In our earlier work on P(III) compounds, we had
noted that P(III) azides react in a manner different from
organic azides.23a−b Hence, to know whether a P(III)
isothiocyanate 47 will react in a manner similar to
the traditional organic isothiocyanate 44 (Scheme 13a,
cf. product 46), we treated the precursor 47 with the
bromoethyl-sulfonamide 45. This reaction did take
place, but in a direction entirely different from the
above, leading to the product 48. In this case, the for-
mation of new P–S and C–S bonds has taken place in
Supplementary Information (SI)
Spectroscopic data for the new compounds reported here will
be available from the authors. Crystallographic data for 25
and 48 have been deposited with the Cambridge Crystallo-
graphic Data Centre as supplementary publication numbers
CCDC 1834021 and 1575674. Copies of the data can be
obtained free of charge, on application to CCDC, 12 Union
Road, Cambridge CB2 1EZ, UK [fax: +44(1223)336033 or e-
mail: deposit@ccdc.cam.ac.uk]. Supplementary information
addition to the oxidation at the phosphorus center. IR, is available at www.ias.ac.in/chemsci.

99 Page 10 of 11
J. Chem. Sci. (2018) 130:99
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support and equipment. KCK thanks CSIR (New Delhi for
a project (02(0240)/15/EMR-II) and DST for the J. C. Bose
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