A Convenient Route to Medium-ring Trisubstituted cis-Olefins from Allenes

SYNTHESIS

International Journal of Methods in Synthetic Organic Chemistry 1975, No. 3: March.

A Convenient Route to Medium-ring Trisubstituted cis-Olefins from Allenes

S.N. Moorthy and R. Vaidyanathaswamy
Department of Chemistry, Indian Institute of Technology, Kanpur 208016, India and D. Devaprabhakara.

Department of Organic Chemistry, Indian Institute of Science, Bangalore, 560012, India.

SYNTHESIS 1975, 194-195.

Georg Thieme Verlag. Stuttgart. Academic Press. New York. London.

Compounds   Yields (%) Coupling constants (J7,8 Hz) M.p.
    a b c    
5, 6-Dehydrokawain (8) 94 71 - 16.3 138-140
Yangonin (9) 93 70 18 16.0 153-154
11- Methoxy-yangonin (10) 66 50 8.7 16.0 163-164
5,6-Dehydromethysticin (11) 80 60 8.0 16.0 232-233

a. Yields obtained by the Witting condensation of 2 with appropriate phosphoranes.
b. Overall yields based on 1.
c. Yields obtained by the method of Bu ‘Lock, et al.1.

6-(trans-1-Propenyl)-4-methoxy-2-pyrone(12), a key intermediate in the total synthesis of d, 1-radicinin (13) has been prepared from 1 by tedious procedures 2,9. Further application of our method for the preparation of the propenyl pyrone 12 provided a facile route to the natural product 13.

Witting reaction of 2 with ethylidenetriphenylphosphorane at room temperature afforded a mixture of 6-trans-(12) and cis-propenyl isomers (14) (ratio~7:3)10 in 54% yield. The cis-isomer (14) was transformed quantitatively into the more stable trans-propenyl derivative (12), when the mixture was merely heated at 120° for 4 h. The structure of 12 was confirmed by comparison of the physical data with those of an authentic sample. Thus, the formal synthesis of radicinin (13) was achieved.

From the above result, our procedure involving the selenium dioxide-oxidation of the 6-methyl group in 2-pyrones followed by the Witting condensation may be applicable for the synthesis of other 6-conjugated 2-pyrones, such as citreoviridin11.

Oxidation of Triacetic Lactone Methyl Ether (1) using Selenium Dioxide:

Method A: A mixture of the pyrone (1; 0,280 g, 2 mmol) and selenium dioxide (1.110 g, 10 mmol) in anhydrous dioxin (8ml) was heated at 180°(outside) in a sealed tube under vigorous stirring. After 1h, the precipitate was removed by filtration and washed with dichloromethane/methanol (20:1). The combined filtrate and washings were concentrated to almost dryness. The residue was separated by silica gel chromatography using dichlorometahe/methanol (20:1) as eluent.
The first fraction: starting material (10 mg)

The second fraction 6-formyl-4-methoxy-2-pyrone (2); yield: 199 mg (65%) 12; m.p. 177-178°.
C7H6O4 calc C 54.55 H 3.92 (154.12) found 54.13 3.84 I.R. (KBr): Vmax =1695, 1565, 1262 cm?1.
1H-N.M.R. (DMSO-d6): ?= 3.90 (s, 3H), 5.98 (d, 1H, J= 2.1 Hz), 7.09 (d, 1H, J=2.1 Hz), 11.38 ppm (s, 1H).
Mass spectrum: m/e=154 (M+; 24), 125 (100%), 69 (37%).

The third fraction: 6-hydroxymethyl-4-methoxy-2-pyrone (3); yield: 76 mg (25%) 12; m.p. 178-179° (m.p. 180-181°)3.
I.R. (KBr): Vmax =3360, 1720, 1700, 1560 cm?¹.
1H-N-M.R. (DMSO-d6): ?=3.81 (s, 3H), 4.23 (d, 2H, J=6.2 Hz, changed to singlet by adding D2O), 5.55 (broad d, 1H, J=2Hz), 5.57 (broad t, 1H, J= 6.2 Hz, disappeared by adding D2O), 6.08 ppm (m, 1H).

Mass spectrum: m/e= (M+, 28%), 125 (100%), 69(26%).
Oputinol acetale (6-acetoxymethyl-4-methoxy-2-pyrone); m.p. 110-111° (m.p. 110-111°)3.
1H-N.M.R. (CDCI3): ?=2.15 (s, 3H), 3.85 (s, 3H), 4.85 (s, 2H), 5.50(d, 1H, J=2Hz), 6.05 ppm (d, 1H, J=2H).
Method B: In the above oxidation, when heating was prolonged for additional 2h, the yield of pyrone (2) was increased to 75% (221 mg) ¹² recovering a small amount of starting material (12 mg), whereas no hydeoxymethyl pyrone (3) was obtained.

Methylation of 3, 5, 6-Trimethyl-4-hydroxy-2-pyrone (4):

A mixture of the pyrone (4: 308 mg, 2 mmol), dimethyl sulfate (0.300g), and potassium carbonate (1,500 g) in ethyl methyl ketone was refluxed for 11 h with stirring. The reaction mixture was filtered and washed with acetone. The combined organic solvents were evaporated under reduced pressure. The residue was chromatographed on silica gel with dichloromethane as eluent to give two isomeric products, 5 and 6.

3, 5, 6-Trimethyl-4-methoxy-2-pyrone (5); yield: 149 mg (44%); colorless oil.
I.R. (Neat); Vmax=1689, 1635, 1550, 1340 cm?¹.
1H-N.M.R (CDCI3): ?=1.95 (s, 3H), 2.05 (s, 3H), 2.24 (s, 3H), 3.86 ppm (s, 3H).
Mass spectrum: m/e=168 (M+, 91%), 140(100%), 125 (76%), 97 (60%), 83 (73%).
3, 5, 6- Trimethyl-2-methoxy-4-pyrone (6); yield: 72 mg (21%); m.p. 82-84°.
I.R. (KBr): Vmax=1664, 1587, 1320 cm?¹.
1H-N.M.R. (CDCI3): ?=1.84 (s, 3H), 1.93 (s, 3H), 3.95 ppm (s, 3H).
Mass Spectrum: m/e=168(M+, 100%), 153 (68%), 125 (30%), 97 (30%), 83 (34%).
C9H12O3 calc. C 64.25 H 7.26
(168.19) found 64.27 7.19

3, 5-Dimethyl-6-formyl-4-methoxy-2-pyrone (7):

A mixture of the trimethyl pyrone (5; 66 mg, 0.39 mmol) and selenium dioxide (222 mg, 2 mmol) in dioxan (0.5 ml) was heated at 165° for 1h in a sealed tube with stirring. The similar work-up as described in the oxidation of 1 provided the monoformyl pyrone (7); yield: 37 mg (52%); m.p. 113-114°.
I.R. (KBr): Vmax = 1720, 1679, 1630, 1560 cm?¹.
Mass spectrum: m/e=182 (M+, 56%), 153 (74%), 125 (26%), 97 (100%).
1H-N.M.R. (CDCI3); ?=2.13 (s, 3H), 2.49 (s, 3H), 3.87 (s, 3H), 10.63 ppm (s, 1H).

5, 6-Dehydrokawain (8):

To a mixture of the formyl pyrone (2; 31 mg, 0.2 mmol) and benzyltriphenylphosphonium chloride (11.6 mg, 0.3 mmol) in dimethyl sulfoxide (1 ml), sodium hydride (52.9% in mineral oil, 0.3 mmol) was added under cooling and then stirred for 4 in at room temperature. The reaction mixture was poured into saturated aqueous sodium chloride, extracted with ethyl acetate, dried, and evaporated in vacuo. The product thus obtained was purified by silica gel chromatography using benzene/tetrahydrofuran (3:1) as eluent; yield: 43 mg (94%) : m.p. 138-140°. The physical data of 8 were in agreement with those of the natural 5,6-dehydeokawain7.
Other 6-conjugated-4-methoxy-2-pyrones, 9-11, were prepared in the similar manner.

6-(trans-1-Propenyl)-4-methoxy-2-pyrone (12):

The formyl pyrone (2; 26 mg, 0.17 mmol) was added to a cold solution of ethylidenetriphenylphosphorane, prepared from ethyltriphenylphosphonium bromide(95 mg, 0.24 mmol) in the presence of sodium hydride (52.9% in mineral oil, 0.3 mmol) in dimethyl sulfoxide (1ml), and then brought to room temperature. After 10 min, the reaction mixture was poured into saturated aqueous sodium chloride, extracted with ethyl acetate, dried and evaporated in vacuo. The residue was chromatographed on silica gel using dichloromethane as eluent; yield: 15 mg (54%).

The resulting crystalline mixture of trans-(12) and cis-propenyl isomers (14) was heated at 120° in a sealed tube under nitrogen atomosphare to give trans-1-propenyl pyrone (12) quantitatively; colorless needles, m.p. 102-104° (m.p 102-103°)9.

Mass spectrum: m/e = 166 (M+, 87%), 138 (83%), 125 (100%), 69 (58%).

The I.R. spectrum and the ¹H-N.M.R. spectrum of 12 were identical with those of an authentic sample obtained by kato, et al9.

References

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  10. The ratio was determined from the ¹H-N.M.R. spectrum.
  11. N.Sakabe, T. Goto, Y. Hirata, Tetrahedron Lett. 1964, 1825.
  12. Corrected yields.

A convenient Route to Medium-ring Trisubstituted cis-Olefins from Allens.

S.N. MOORTHY and R.VAIDYANATHASWAMI*

Department of Chemistry, Indian Institute of Technology, Kanpur 208016, India and D.DEVAPRABHAKARA.
Department of Organic Chemistry, Indian Institute of Science, Bangalore 560012, India.

The selective introduction of a trisusbstituted carbon-carbon double bond with a specific configuration is still an interesting problem to organic chemists, although several methods have been documented in the literature1-4. The sodium/ammonia reduction of allenes, in combination with an elegant synthesis of allenes has proven to be useful in synthesizing a homologue of an olefin or a diene in good yield 5-11. In this communication, we report a further extension of this general method to provide a new and a convenient procedure to synthesize medium-ring (9 and 10 membered) tri-alkyl-substituted cis-olefins.

1-Methyl-1,2-cyclodecadiene (2) was prepared starting from 1-methylcyclooctene (1) in one step by the method of Untch and co-workers¹². The treatment of a four-fold excess of 1 with 1 equivalent of tetrabromomethane and 2 equivalents of methyllithium in diethyl ether at ca. -65° gave 2 in 65% yield based on tetrabromomethane. The structure of the allene 2 was established by elemental analyses and I.R.-spectroscopy.

Sodium/ammonia reduction of 1-methyl-1, 2-cyclodecadiene (2) provided mainly cis-1-methylcyclononene (3) (95%), in excellent yield. the identy of 3 was unequivocally established by elemental analyses and spectral properties. In a similar manner, we have transformed 3 to cis-1-methylcyclodecene (4), in good yield. Thus, these results indicate that the reduction of such trialkylsubstituted allenes is highly regiospecific as well as stereoselective.

In the absence of a protonating agent, it is reasonable to assume the formation of an allylic dianion during the reduction of an allenic system by sodium/ammonia. We propose that the least substituted end of the dianion carries the greater amount of charge, since the electron pair could occupy an orbital containing more s character when concentrated there. If this is so, one expects preferential protonation at the least substituted carbon to yield the thermodynamically more stable olefin. Our results demonstrate this expected behaviour of the allylic dianion intermediate, and thereby provides a simple and an effective synthetic route to such trialkylsubstituted olefins.

1-Methyl-1, 2-cyclononadiene:

Following the procedure of Untch and co-workers¹², from 1-methylcyclooctene (9.9 g, 0.08 mol), tetrabromomethane (6.6g, 0.02 mol) and methyllithium in diethyl ether ( 40 ml; 0.04 mol), there was obtained 1-methyl-1,2-cyclodecadiene; yield:1.7 g (65%); b.p.66-67°/16 torr. The product was found to be homogeneous on a 10′x ¼” Carbowax 20M-Ag NO3 column.
C10H16 calc. C 88.16 H 11.84.
(13.62) found 87.90 11.65
I.R. (neat) Vmax = 1940 (ms) cm?¹.

Cis-1-Methylcyclononene:

1-Methyl-1, 2-cyclodecadiene (1.3 g, 0.01 mol) was reduced with sodium (1.2 g, 0.05 g-atom) in liquid ammonia7 (100 ml) to give cis-1-methylcyclononene: yield: 1.1g (85%): b.p.54-55°/10 torr. G.L.C analysis on a 10′x ¼” Carbowax 20M-AgNO3 column showed the presence of two components in the ratio 95:5. The major product (95%) was separated by preparative G.L.C. and identified by the usual procedure. The minor product (5%) could not be identified.
C10H18 calc C 86.96 H 13.04
(138.3) found 86.85 12.98
I.R. (neat): Vmax = 1620 (w), 865 (ms) cm?¹.
¹H-N.M.R. (CCL4): ?=5.26 (t, J=8.0 Hz, 1H), 1.68 (s, 3H), 2.10-1.20 ppm (m, 14 H).

1-Methyl-1, 2-cyclodecadiene:

From 1-methylcyclononene (11.0 g, 0.08 mol), tetrabromomethane bromide (6.,6g, 0.02 mol), and methyllithium in diethyl ether (40 ml; 0.04 mol), there was obtained 1-methyl-1,2-cyclodecadiene: yield:1.8 g (62%): b.p. 68-69°/2 torr. G.L.C. analysis of the product on a 10′x¼” Carbowax 20 M-AgNO3 column indicated it to be pure.
C11H18 calc C88.00 H 12.00
(150.3) found 87.87 11.90
I.R. (neat): Vmax = 1940 (mms) cm?¹.

Cis-1-Methylclodecene:

1-Methyl- 1,2-cyclodecadiene (1.5 g, 0.01 mol) was reduced with sodium (1.2 g, 0.05 g atom) in liquid ammonia (100 ml) to give cis-1-methylcyclodecene; yield: 1.2 g (80%): b.p. 82-83°/14 torr. G.L.C. analysis on a 10′x¼” Carbowax 20M-AgNO3 column indicated it to be pure to the extent of 94%. The major component (94%) was separated by preparative G.L.C. and identified by the usual procedure. Our attempt to identify the minor component (6%) was not successful.
C11H20 calc. C 86.84 H 13.16
(152.3) found 86.82 12.96
I.R. (neat): Vmax = 1620 (w) 860 (ms) cm?¹.
¹H-N.M.R. (CCL4):?=5.10 (t, J=8.0 Hz, 1 H), 1.65 (s, 3H), 2.30-1.20 ppm (m, 16 H).
The authors gratefully acknowledge the financial support from Indian Institute of Technology, Kanpur 208016, India.

References

Present address: Agriculture Chemicals Division, Indian Agricultural Research Institute, New Delhi 110012, India.

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REACTIONES ORGANICAE

New methods in synthetic organic chemistry selected from the current chemical literature.

Reduction of Aryl Iodides
R=H; 2-, 3-or 4-CH3, or OCH3; 3-COOH; Yield: 75-100%.

Hydrogenolysis of aryl iodides with sodium hydride is carried out in dry tetrahydrofuran solution by refluxing it for 24-72 h. [Full experimental details]

R.B. Nelson, G.W. Gribble, J. Org. Chem. 39, 1425 [1974].

Phloroglucinol and Phloroglucinol Trimethyl Ether.
Phloroglucinol (3) can be prepared simply and efficiently by treatment of 1,3,5-tribromobenzene (1) with excess sodium methoxide in methanol/dimethylformamide in the presence of a catalytic amount of copper (1) iodide and hydrolysis of the resultant phloroglucinol trimethyl ether (2) with concentrated hydrochloric acid in 85-95% yield. [Full experimental details].
A.Mckillop, B.D.Howarth, R.J. Kobylecki, Synth, Commun. 4, 35 (1974)

Decomposition of Naphtahlenediazonium Mercury (II) Bromide Complexes.

The naphthalenediazonium mercury [1] bromide complexes 1and 3, respectively [prepared from the corresponding amines by diazotation and treatment with mercury (II) bromide according to H.W. Schwechten, Ber, dtsch, chem. Ges, 65, 1605 (1932)] are decomposed to the naphthalenes 2 and 4 by stirring compounds 1 and 3 in hexamethylphosphoric triamide, in the presence of powdered soft glass, for 10 min. [Full experimental details].

M.S.Newman, W.M. Hung, J.Org. Chem. 39, 1317 (1974).

1-Alkyl (aryl) thio-2-chloro-1-pheny-2-phenylthioethenes by Chlorination with Sulfenyl Chlorides.

1-Alkyl (aryl) thio-1-phenyl-2-phenylthioethenes (1; prepared from 1-alkyl (aryl) thio-1-phenylethenes and phenyl sulfenyl chloride in tetrachloromethane) are chlorinated with arylsulfenyl chlorides (2) in tetrachloromethane at room temperature to give the title compounds 3 together with diaryl disulfides. Although hydrogen chloride is evolved, the expected 2, 2 -bis [arylthio]-1-alkyl (aryl) thio-1-phenylethenes are not formed. [Full experimental details].

M.Oki.K. Kobayashi, Bull. Chem. Soc. Japan 46, 687 (1973).