Dodecamethyl-1λ3,4λ3-diphospha-2,3,5,6,7,8-hexastannabicyclo[2.2.2]octane, a Highly Symmetrical...

2
kov sense. In spite of contrary predictions"'I cyclization (5)-(7) readily takes place, if a tertiary carbenium ion is formed'''. The deprotonation of cyclopentyl cations (7) is reversible so that only the thermodynamically most stable elimination products (6) are isolated. Procedure ZnClz (2.2 g) was dissolved in ether (2.6 mL), diluted with 45 mL of CH2C12 and cooled to - 78°C. Successively, solutions of (3c) (5.30 g, 63.0 mmol) and (Ib) (2.64 g, 19.9 mmol) each in 10 mL of CHZCI2 were added dropwise. After 1.5 h at - 78 "C the catalyst was extracted with conc. aqueous NH3 and the organic phase was dried over CaC12. The crude product, obtained after evaporation of the sol- vent and excess alkene, was added to a solution of ZnCIz (4.4 g) in ether (5.2 mL) and CH2C12 (90 mL) at 25°C. A stream of dry HCI was bubbled through the solution for ca. 1 min. After 35 min at 25"C, the mixture was worked-up with aqueous ammonia as described above. Distillation yielded 2.50 g (70%) of pure octamethylcyclopentene (6JI. Received: July 22, 1981 [Z 923 IE] German version: Angew. Chem. 93, 1069 (1981) [I] a) H. M. R. Hoffmann, Angew. Chem. 85, 877 (1973); Angew. Chem. Int. Ed. Engl. 12. 819 (1973); b) R. 8. Woodward. R. Hoffmann, ibid. 81. 797 (1969) and 8, 781 (1969); c) J, E. Baldwin, J. Chem. SOC. Chem. Commun. 1976. 734. [21 a) Y. Hayakawa, K. Yokoyama, R. Noyori. J. Am. Chem. SOC. 100. 1791 (1978); b) M. W. E. M. van Rlborg, R. van Doom. N. M. M. Nibbering. Org. Mass Spectrom. 15, 152 (1980); c) H. M. R. Hoffmann, R. Chidgey. Tetrahedron Lett. 1978. 85; d) H. Sakurai. A. Shirahafa. A. Hosomi. An- gew. Chem. 91. 178 (1979); Angew. Chem. Int. Ed. Engl. 18, 163 (1979). 131 a) A. Milier. M. Moore, Tetrahedron Lett. 1980, 577; b) H. Klein. A. Erbe, H. Mayr. Angew. Chem., in press. [4] a) Catalyst system: H. Mayr, I. K. Halbersfadf. Angew. Chem. 92, 840 (1980); Angew. Chem. Int. Ed. Engl. 19, 814(1980); b) Rules for selective formation of 1 : 1-addition products: H. Mayr, ibid. 93, 202 (1981). 20, 184 (1981). [5] (44: B.p.= 55-65°C (bath)/2 torr; 'T-NMR (CDCI,): 6= 11.92, 13.20, 22.02, 31.85, 33.4 (5 q), 40.19 (d), 50.30 (t), 71.20 (s), 118.43 (d), 140.00 [6] C. K. Ingold. J. Chem. SOC. 119, 305 (1921); G. S. Hammond in M. S. Newmnn: Steric Effects in Organic Chemistry, Wiley, New York 1956, p. 460 pp; B. Capon. S. P. McManus: Neighboring Group Participation, Plenum Press, New York 1976, Vol. 1, p. 58 pp. (s). 171 (3d) gives a complex mixture of 1 : I-products with (la). [8] The 1,1,2,3-tetramethylallyl cation is, however, attacked by isobutene to an extent of 15% at the more highly substituted end (Table I, footnote k1)- 191 Analogous cyclizations of the prenyl chloride-olefin-addition products must proceed via secondary cyclopentyl cations and were not observed PbI. Dodecamethyl-1 L3,4L3-diphospha-2,3,5,6,7,8- hexastannabicycloI2.2.2bctane, a Highly Symmetrical Cage Molecule[**' By Martin Drager and Bernd Mathiasch"' Dedicated to Professor Leopold Horner on the occasion of his 70th birthday The reaction of white phosphorus with tin hydrides can be used to form SnP bonds"]. In addition to the phos- phane, we obtained the title compound (I) by reacting ['I Prof. Dr. M. DrPger, Dr. 9. Mathiasch Institut fur Anorganische Chemie und Analytische Chemie der Univer- sitst Johann-loachim-Becher-Weg 24, D-6500 Mainz (Germany) by the Fonds der Chemischen Industrie. I**] This work was supported by the Deutsche Forschungsgemeinschaft and 1,1,2,2-tetrarnethyldi~tannane~~~ with phosphorus in the dark. Under the action of light (I) disproportionates to the nor- bornane-analogous (2)l" and dimethylstannanediyl, which can be trapped as iodotrimethylstannane by reaction with CH3I. hv [(CH3hSnJ6P2 - [(CH~ZS~I~PZ +- (CHdzSn: (1) (2) The novel compound (1) forms as bright yellow crystals from benzene. The X-ray structure analysis'31 indicates, within the standard deviations, a chiral molecule with D3 symmetry (six equivalent Sn atoms, two equivalent P atoms and six equivalent C atoms; cf. Fig. 1). The bicycle Sn,P2 is constructed from three Sn4P2six-membered rings which share three bonds with each other and adopt the conformation of a boat, twisted by 26". L Fig. I. Molecular structure of (1) in the crystal with average bond lengths [pm] (P.. .P distances; intramolecular 518, intermolecular 371 pm) and sym- metry elements. Average bond- and torsion-angles I"]: Sn-P-Sn 98, P-Sn-Sn 117, C-Sn-C 107, Sn-Sn-C 109, P-Sn-C 107; PSn-SnP f26, SnSn-PSn -62, SnSn-PSn' f37. In solution at room temperature (I) has, on average, Djh symmetry: The NMR signals of all the methyl groups show a joint doublet arising from 31P-coupling[41. The coupling constants 'J(PSnCH) and 'J(PSnC) confirm the previously found dependence on the torsion angle of the phosphorus lone pair of electrons and the coupling nuclei in (2)l'I. Procedure All operations are performed under argon, using sol- vents saturated with Ar: Me,Sn2Cl2 (4 g, 10.9 mmol) is re- duced to Me4SnzH2at room temperature by LiAIH, in 70 mL of Et20. The solution is cooled to 0°C and ice-water added under stirring. The ether layer is separated off, dried over MgS04, and poured onto white phosphorus (0.3 g, 9.7 mmol, less than the stoichiometric amount). The reaction vessel is kept dark and immediately cooled (OOC). After 48 h the phosphorus is consumed, and the crystals formed are separated from the EtzO solution by suction and re- Angew. Chem. Int. Ed. Engi. 20 (198t) No. 12 8 Veriag Chemie GmbH, 6940 Weinheim. 1981 0570-0833/81/1212-1029 $02.50/0 1029

Transcript of Dodecamethyl-1λ3,4λ3-diphospha-2,3,5,6,7,8-hexastannabicyclo[2.2.2]octane, a Highly Symmetrical...

Page 1: Dodecamethyl-1λ3,4λ3-diphospha-2,3,5,6,7,8-hexastannabicyclo[2.2.2]octane, a Highly Symmetrical Cage Molecule

kov sense. In spite of contrary predictions"'I cyclization (5)-(7) readily takes place, if a tertiary carbenium ion is formed'''. The deprotonation of cyclopentyl cations (7) is reversible so that only the thermodynamically most stable elimination products (6) are isolated.

Procedure

ZnClz (2.2 g) was dissolved in ether (2.6 mL), diluted with 45 mL of CH2C12 and cooled to - 78°C. Successively, solutions of (3c) (5.30 g, 63.0 mmol) and (Ib) (2.64 g, 19.9 mmol) each in 10 mL of CHZCI2 were added dropwise. After 1.5 h at - 78 "C the catalyst was extracted with conc. aqueous NH3 and the organic phase was dried over CaC12. The crude product, obtained after evaporation of the sol- vent and excess alkene, was added to a solution of ZnCIz (4.4 g) in ether (5.2 mL) and CH2C12 (90 mL) at 25°C. A stream of dry HCI was bubbled through the solution for ca. 1 min. After 35 min at 25"C, the mixture was worked-up with aqueous ammonia as described above. Distillation yielded 2.50 g (70%) of pure octamethylcyclopentene (6JI.

Received: July 22, 1981 [Z 923 IE] German version: Angew. Chem. 93, 1069 (1981)

[ I ] a) H. M. R . Hoffmann, Angew. Chem. 85, 877 (1973); Angew. Chem. Int. Ed. Engl. 12. 819 (1973); b) R . 8. Woodward. R . Hoffmann, ibid. 81. 797 (1969) and 8, 781 (1969); c) J, E. Baldwin, J. Chem. SOC. Chem. Commun. 1976. 734.

[21 a) Y. Hayakawa, K . Yokoyama, R . Noyori. J. Am. Chem. SOC. 100. 1791 (1978); b) M. W. E. M. van Rlborg, R . van Doom. N. M. M . Nibbering. Org. Mass Spectrom. 15, 152 (1980); c) H. M. R. Hoffmann, R. Chidgey. Tetrahedron Lett. 1978. 85; d) H. Sakurai. A. Shirahafa. A . Hosomi. An- gew. Chem. 91. 178 (1979); Angew. Chem. Int. Ed. Engl. 18, 163 (1979).

131 a) A. Milier. M. Moore, Tetrahedron Lett. 1980, 577; b) H. Klein. A. Erbe, H . Mayr. Angew. Chem., in press.

[4] a) Catalyst system: H. Mayr, I . K. Halbersfadf. Angew. Chem. 92, 840 (1980); Angew. Chem. Int. Ed. Engl. 19, 814(1980); b) Rules for selective formation of 1 : 1-addition products: H. Mayr, ibid. 93, 202 (1981). 20, 184 (1981).

[5 ] ( 4 4 : B.p.= 55-65°C (bath)/2 torr; 'T-NMR (CDCI,): 6= 11.92, 13.20, 22.02, 31.85, 33.4 (5 q), 40.19 (d), 50.30 (t), 71.20 (s), 118.43 (d), 140.00

[6] C. K. Ingold. J. Chem. SOC. 119, 305 (1921); G. S. Hammond in M. S . Newmnn: Steric Effects in Organic Chemistry, Wiley, New York 1956, p. 460 pp; B. Capon. S. P. McManus: Neighboring Group Participation, Plenum Press, New York 1976, Vol. 1, p. 58 pp.

(s).

171 (3d) gives a complex mixture of 1 : I-products with (la). [8] The 1,1,2,3-tetramethylallyl cation is, however, attacked by isobutene to

an extent of 15% at the more highly substituted end (Table I , footnote k1)-

191 Analogous cyclizations of the prenyl chloride-olefin-addition products must proceed via secondary cyclopentyl cations and were not observed PbI.

Dodecamethyl-1 L3,4L3-diphospha-2,3,5,6,7,8- hexastannabicycloI2.2.2bctane, a Highly Symmetrical Cage Molecule[**' By Martin Drager and Bernd Mathiasch"' Dedicated to Professor Leopold Horner on the occasion of his 70th birthday

The reaction of white phosphorus with tin hydrides can be used to form SnP bonds"]. In addition to the phos- phane, we obtained the title compound (I) by reacting

['I Prof. Dr. M. DrPger, Dr. 9. Mathiasch Institut fur Anorganische Chemie und Analytische Chemie der Univer- sitst Johann-loachim-Becher-Weg 24, D-6500 Mainz (Germany)

by the Fonds der Chemischen Industrie. I**] This work was supported by the Deutsche Forschungsgemeinschaft and

1,1,2,2-tetrarnethyldi~tannane~~~ with phosphorus in the dark.

Under the action of light ( I ) disproportionates to the nor- bornane-analogous (2)l" and dimethylstannanediyl, which can be trapped as iodotrimethylstannane by reaction with CH3I.

hv [(CH3hSnJ6P2 - [ ( C H ~ Z S ~ I ~ P Z +- (CHdzSn:

(1) (2)

The novel compound (1) forms as bright yellow crystals from benzene. The X-ray structure analysis'31 indicates, within the standard deviations, a chiral molecule with D3 symmetry (six equivalent Sn atoms, two equivalent P atoms and six equivalent C atoms; cf. Fig. 1). The bicycle Sn,P2 i s constructed from three Sn4P2 six-membered rings which share three bonds with each other and adopt the conformation of a boat, twisted by 26".

L

Fig. I. Molecular structure of (1) in the crystal with average bond lengths [pm] (P.. .P distances; intramolecular 518, intermolecular 371 pm) and sym- metry elements. Average bond- and torsion-angles I"]: Sn-P-Sn 98, P-Sn-Sn 117, C-Sn-C 107, Sn-Sn-C 109, P-Sn-C 107; PSn-SnP f26, SnSn-PSn -62, SnSn-PSn' f 3 7 .

In solution at room temperature (I) has, on average, Djh symmetry: The NMR signals of all the methyl groups show a joint doublet arising from 31P-coupling[41. The coupling constants 'J(PSnCH) and 'J(PSnC) confirm the previously found dependence on the torsion angle of the phosphorus lone pair of electrons and the coupling nuclei in (2)l'I.

Procedure

All operations are performed under argon, using sol- vents saturated with Ar: Me,Sn2Cl2 (4 g, 10.9 mmol) is re- duced to Me4SnzH2 at room temperature by LiAIH, in 70 mL of Et20. The solution is cooled to 0°C and ice-water added under stirring. The ether layer is separated off, dried over MgS04, and poured onto white phosphorus (0.3 g, 9.7 mmol, less than the stoichiometric amount). The reaction vessel is kept dark and immediately cooled (OOC). After 48 h the phosphorus is consumed, and the crystals formed are separated from the EtzO solution by suction and re-

Angew. Chem. Int. Ed. Engi. 20 (198t) No. 12 8 Veriag Chemie GmbH, 6940 Weinheim. 1981 0570-0833/81/1212-1029 $02.50/0 1029

Page 2: Dodecamethyl-1λ3,4λ3-diphospha-2,3,5,6,7,8-hexastannabicyclo[2.2.2]octane, a Highly Symmetrical Cage Molecule

crystallized from benzene: yield 0.5 g (22%, relative to P), bright yellow, highly refractive crystals, m. p. = 220°C (de- camp.), readily soluble in CH2Cl2.

Received: February 1, 1980; publication delayed at the authors' request 12 929 IE]

German version: Angew. Chem. 93, 1079 (1981)

[I] 8. Mathiasch. M. Druger. Angew. Chem. 90. 814 (1978): Angew. Chem. Int. Ed. Engl. 17, 767 (1978); B. Mathiasch. J. Organomet. Chem. 165. 295

121 B. Mathiasch, Inorg. Nucl. Chem. Lett. 13, 13 (1977); J. Organomet. Chem. 141. 295 (1977).

131 Cell data: a=1742.7(2), b= 1026.5(2), c = l627.2(2) pm, /3= 104.74(2)", V=2815.106 pm', space group C2/c, Z=4, ~ ~ . ~ ~ ~ = 2 . 2 5 , p,,,=2.22 g

cm-'; 3227 reflections (A=71.069 pm) of which 512 were unobserved ( < 2u). CADCdiffractometer, R = 0.022, H atoms not considered.

[4] NMR data (in CD2C12, re!. TMS or H,P04 ext.): 'H: 6=0.55, 'J(PSnCH)= 2.6, 2J( '"SnCH)=43.4, 2J( '"'SnCH) = 45.4, 'J(SnSnCH) = 15.6 Hz; 'T: 6 = -4.28, 'J(SnC)=218, 2J(PSnC)= 11.0 Hz; "P: 6= - 299, 'J( "'SnP) = 7 14, 'J( "%P) = 749, 'J(SnSnP)= 93 Hz.

(1979).

Direct Diastereoselective Alkylation of Tartaric Acid Through an Enolate By Reto Naef and Dieter Seebach"'

The usefulness of (+)- and (-)-tartaric acid as chiral starting materials (pool of chiral building blocks1l1) for syn- theses would be greatly enhanced, if direct alkylation to give (I) could be achieved. Depending upon the stereo- chemical course of such a process, natural products with erythro-(I) structures['', such as piscidic acid, fukiic acid, or loroglossine, which have hitherto been synthesized only as (-+)-mixtures by elaborate routes, might become read- ily accessible in enantiomerically pure form.

We have now succeeded in finding conditions for gener- ating lithium enolates (2a) and (2b) from (R,R)-tartrate

'ENOLATE

IC-0 n

6 O O H i 1) (Za), R = CH, i2c i

/2h), R = CH(CH3)Z

acetonide~'~'. Alkylation with highly reactive electrophiles leads to pentasubstituted trans/cis-dioxolanes (3)/(4) in yields ranging from 40 to 80% (Table 1); the diastereomeric ratios of ca. 80 : 20 can be determined from the 'H-NMR spectra. The stability of the enolates (24 and (26). sufficient for allylations and benzylations but not for n-alkylations, can be rationalized by assuming, that the rigid acetonide skeleton holds the enolate n-system and the C-0 0 bond at an "aldol distance", perpendicular to each other [(2c)141, thus preventing 0-elimination.

The enolate (2a) also adds to the carbonyl group of acetone: A 4:l-mixture of a diester of (4fl and of the lactone ester (5) (M.p.=96-97"C, [a]:= - 11.0 (c=0.95, CHCI,)), which spontaneously crystallizes, is isolated in 6Ooh yield. The minor component (5) must be a cis-bicy- clo[3.3.0] system formed from an adduct of type (3) with

[*I Prof. Dr. D. Seebach, DipLChem. R. Naef Laboratorium fur Organische Chemie der Eidgeniissischen Technischen Hochschule ETH-Zentrum, Universitatstrasse 16, CH-8092 Zurich (Switzerland)

trans-configuration. Thus, acetone has approached the enolate (2a) from the Re-face preferentially [see (4fl in Ta- ble I]. In contrast, the p-methoxy-benzyiation of (Za) must

(3) [u), R' = CH, (4) ih) , R' = CH(CH,),

(2 R , 3 R ) -threo-i6) ( Z R , SS)-erythro-I7) (+)-piscidic acid

have occurred from the Si-face: the diastereomeric mixture (3e)/(4e) was hydrolyzed with 0.1 N HCI (methanollwater 1 : I ) to give the dihydroxyester, the major isomer of which was obtained by crystallization. According to the 'H- and I3C-NMR spectra, supported by measurements in the pres- ence of a chiral shift reagent, and comparison with an au- thentic the major product is the 97% enantiom- erically pure threo-isomer (6) (m. p. = 107.0- 107.5, [a]g= - 26.3 (c=O.57, CHCI,)), while natural piscidic acid is ery- fhro-(i'). By analogy, we assume that all main products of allylation and benzylation of (2) have the trans-coniigura- tion (Table I), i . e. that the substitution of the a-proton of tartaric acid occurs with retention of configuration.

Table I. Ratios of diastereorners, yields, and specific rotations of the products ob- tained from alkylations of (2). The yields refer to distilled samples (3)+ (41, the rota- tions of which are given without diastereomer enrichments.

Educt Products (3)f (4) (2) El R' Yield I&'

[%] (3) $4) (c in CHCI,)

(2a) Ally1 bromide (a) CH2CH=CH2 65 87: 13 - 19.1" (1.52) (26) Crotyl bromide (b) CH2CH=CHCH, 46 78 :22 - 16.7" (1.08) (2c) I-Bromo-3-me- (c) CH2CH=C(CH,)2 75 82 : I8 -28.8" (0.58)

(20) Benzyl bromide (d) CH2C6HS 54 84: 16 -37.8" (1.00) (2a) p-Methoxy- (el p-C,HIOCH2 77 82: 18 -38.8" (5.58)

(20) Acetone 0) C(OH)(CH,)2 601al + 15.2" (2.57) [b]

thyl-2-butene

benzyl bromide

[a] Total yield of (4fl and (5% ratio 4 : I . [bl Rotation value of pure (411.

Procedure

(3d)/(4d): To a solution of dimethyl (R,R)-tartrate ace- tonide (3.27 g, 15 m m ~ l ) [ ~ ~ and benzyl bromide (3.06 g, 18 mmol) in 50 mL of tetrahydrofuran (THF)/IO mL of hexa- methylphosphoric triamide, stirred under argon at - 78 "C, is added within 30 min a solution of lithium diisopropyl- amide (16 mmol) in 50 mL of THF cooled at -70°C. The temperature is allowed to rise to - 10°C over 6 h, the reac- tion mixture poured into 300 mL of diethyl ether, the re- sulting solution washed with water ( 5 x 200 ml), dried over magnesium sulfate, and the solvent removed by evapora- tion. Kugelrohr distillation (165 "C/0.005 torr) gives 2.5 g (54%) of the mixture (3d)/(4d) (84 : 16) as a yellow resin.

Received: July 6, 1981 [Z 939 IE] German version: Angew. Chem. 93, I 1 13 (1981)

1030 0 Verlag Chemie GmbH, 6940 Weinheim, 1981 0S70-0833/81/1212-1030 $02.50/0 Angew. Chem. Inl. Ed. Engl. 20 (1981) No. 12