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: [email protected]; [email protected] 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) β ◦ catalyzed addition to the -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)sulfonamide afforded an unusual product with the formula ( (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 The enormous reactivity of organic substrates possess- these are also useful in diverse catalytic transforma- ing sp-hybridized carbon, as in alkynes or allenes, has tions. Some aspects of reactions of these substrates from led to numerous synthetic methodologies. 1 In many our research group will be highlighted in this short reactions involving alkynes, allenic intermediates have paper. been proposed or isolated and in some cases this feature has been utilized as a synthetic route to spe- 2. Experimental cific class of allenes (cf. Figure 1). 1,2 Ynamides are also a special type of alkynes in which the reac- Solvents were dried according to known methods as tivity may depend on the ketenimium species that appropriate. 6 1H, 13C and 31P NMR spectra (1H-400 MHz are analogous to allenes. 3 Another class of alkynes, 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 typical of normal alkynes but can show additional in CDCl3 (unless stated otherwise) with shifts referenced to features because of the conjugated system. 4 Perhaps SiMe4 (δ = 0). IR spectra were recorded on an FTIR spec- more interesting correlation is to a system like that of trophotometer. Melting points were determined by using a local hot-stage melting point apparatus and are uncorrected. isothiocyanates (or isocyanates/CO2/CS2) that have a High-resolution mass spectra (HR-MS) were performed using a BRUKER-MAXIS mass spectrometer with ESI-QTOF-II *For correspondence method. 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, −1 1 791, 756, 725, 700 cm ; HNMR(400MHz, CDCl3)δ Figure 1. Some reactive species possessing central 7.68–7.63 (m, 2H), 7.48–7.32 (m, 4H), 7.26–7.21 (m, 4H), sp-hybridized carbon. 7.14–7.01 (m, 7H), 6.99–6.79 (m, 3H), 6.39 (d, J = 6.8Hz, 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); 13CNMR(100MHz, CDCl3)δ 200.0, 151.2, 137.5 (J = 11.6 Hz), 133.3, 132.2, 2.1 Synthesis of (E)-3,5-bis(5,5-dimethyl-2-oxido- 131.9 (J = 10.4 Hz), 131.6 (J = 10.4 Hz), 131.5, 130.6 1,3,2-dioxaphosphinan-2-yl)-4-methyl-5-phenylpent- (J = 106.5Hz,P− C), 130.3, 129.4, 128.9, 128.8, 128.4, = 4-en-2-one (21) (Scheme 6) 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 = 7.2Hz), = . 31 {1 } To an oven dried Schlenk tube, ketone 19 (0.35 g, 1.70 mmol), 31.5, 30.4, 29.7, 22.3 (J 11 4 Hz), 22.2, 20.4., P H NMR (162 MHz, CDCl )δ31.7 (d, J = 4.1 Hz), 12.3 allenylphosphonate 20 (0.45 g, 1.70 mmol), K2CO3(0.047 g, 3 (d, J = 4.1 Hz); LC/MS m/z 471 [M+ +H]. HRMS (ESI): 0.341 mmol) and dry DMSO (5 mL) were added. The con- + tents were sealed under nitrogen atmosphere and stirred at Calcd. for C29H33O5P2 [M +H]: m/z 523.1804. Found: 90 ◦C (oil bath temperature) for 8 h. After completion of 523.1804 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 2.3 Synthesis of (Z)-5-(diphenylphosphoryl)-4- brine solution, dried over anhyd. Na2SO4 and concentrated 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) one (25) (Scheme 6) as the eluent to afford (E)-3,5-bis(5,5-dimethyl-2-oxido- 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 1283, 1071, 916, 829, 735, 704, 635 cm−1; 1H 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 13 1.91 (s, 3H), 1.30 (s, 3H), 0.95 (s, 6H), 0.52 (s, 3H); C (25;lowerRf ) were isolated using hexane-ethyl acetate NMR (100 MHz, CDCl3)δ 199.3, 151.6 (J = 10.4, 5.5Hz), (4:6) as the eluent. Compound 24: Yield: 0.172 g (29%, 136.6 (J = 9.0 Hz), 130.8 (J = 164.9, 12.1Hz, 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, . = . = . −1 1 )δ 6 1 Hz), 57.4 (J 6 3 Hz), 56.2 (J 6 3 Hz), 56.8 754 cm ; H NMR (400 MHz, CDCl3 7.57–7.52 (m, 5H), (J = 117.5, 6.3Hz, 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); 31 {1 } ( )δ = .