-20°C' for 24 h , and the work-up carried out below -40"C, only Sa wa5 formed (98Yn yield). Complexea Sa and Sb have spectroscopic fea- tures similar to 4: the isomers can be easily distinguished by their "P- R coupling patterns in the "P{ 'HJ-NMR spectrum. Correct elemental

iinalyses were obtained.

,',i

171 P. G. Pringle, 5. 1. Shaw, J. Chem. Soc. Daiion Trans. 1983, 889. [81 P. Braunstein, C . d e Meric d e Bellefon, M. Ries, J. Organomei. Chem.

[9] Eur. Pat. 87347 (Atochern). 262 (1984) c' 14.

[ lo] M. C. Grossel, R. P. Moulding, K. R. Seddon, J . Organornet. Chem. 253 (1983) C50.

New Donor-Substituted Vinyl- and Alkynylcyclopropanes as Synthetic Building Blocks** By Schahab Keyaniyan, Michael Apel, Joe Pierce Richmond, and Armin de Meijere* Dedicated to Professor Wolfgang Liittke on the occasion of his 65th birthday

The vinylcyclopropane-cyclopentene rearrangement is one of the most versatile methods for the annelation of five-membered rings."] Enhancement of the rate of this reaction by electron-donating substituents in the I-[*] and especially in the 2-p0sition[~I of the cyclopropane ring is in the extreme case of 2-vinylcyclopropanolates so pro- nounced that cyclization occurs at room temperature. In order to extend the usefulness of the (haIo~inyl)-[~] and al- kynylcyclopropanes[51 developed by us, we have sought ac- cess to the corresponding donor-substituted building blocks, examples of which include compounds 3, 11 and 7.

Ethyl vinyl ether and other enol ethers polymerize upon heating with tetrachlorocyclopropene. On the other hand,

H " b)

2 3 C I

' SiMq

"1

a-elimination of I , 1,3,3-tetrachloropropene produced the carbene 1,3,3-trichloro-2-propenylidene, which added to ethyl vinyl ether to give 1 -chloro- I-(2,2-dichlorovinyl)-2- ethoxycyclopropane 2 (46%, E/Z= 2.0)14" (Scheme I) . As in the case of I-chloro- I -(trichlorovinyl)cyclopropanes,f5J reaction of 2 with MeLi followed by quenching with elec- trophiles affords substituted alkynylcyclopropanes such as 1 (57%, with Me,SiCl).['I However, the yield upon reduc- tion of 1 to 4 was disappointing (30%).

A substantial improvement was achieved by the newly developed sequence in which the ring chlorine in 2 is se- lectively removed by ultras~nication['~ with zinc/copper to yield 3 (82%, E / Z = 1.0) without retention of configura- tion.18] The dehydrochlorination of 3 to give the chloroace- tylene 6 was best achieved['] (77%, E/Z= 1.5) with potas- sium hydroxide in CH,C12/dibenzo-[ 18]crown-6.["'] Reac- tion of 6 with lithium dialkylamides affords ynamines'"] such as 8 (38%, not optimized, E/Z= 1.0). Halogen-metal exchange followed by substitution with electrophiles con- verted 6 via 5 into synthetically interesting building blocks, the I-alkynyl-2-ethoxycyclopropanes 7 (7a, 590/0, E/ Z=O.5; 7b, 78%, E/Z=0.83).[61 The diastereomers of 7b could be separated by chromatography on silica gel.

Surprisingly, the addition of thermally ring-opened te- trachlorocy~lopropene[~" h1 to vinyl acetate was achieved without polymerization and afforded 10 (85%, E/Z= 0.61), which could be selectively reduced to 2-(trichlorovinyl)cy- clopropyl acetate 11, a potential precursor to building blocks analogous to 7 and 8 (Scheme 2).

12 13 6 14 0

0 II

g, I E t O E t O

7a. E = H 8 E ' NEt2

\

7a. E = H 8 7b, E = C02Me

Scheme 1. a) I ) MeLi, tetrahydrofurdne (THF), -35°C; a ) Me3SiCI, -35°C-RT. b) Zn /Cu , T H F / H 2 0 @ / I ) , ultrasonication, 6 5 T , 20 h. c) LiAIH,, THF, A, 10 h. d) KOH, CH2CI2, dibenzo-[18]crown-h, 24 h. e) nBuLi, THF/n-hexane, -78°C. f ) MeOH (-7a); CICOzMe (-7b). g) LiNEt2, Et,O, -20°C.

[*I Prof. Dr. A. d e Meijere, Dr. S . Keyaniyan, M. Apel, Dr. J . P. Richmond Institut fur Organische Chemie der Universitat Martin-Luther-King-Platz 6, D-2000 Hamburg 13 (FRG)

[**I This work was supported by the Deutsche Forschungsgerneinschaft, the Fonds der Chemischen Industrie, a5 well as by a NATO Research Grant, Hoechst AG, and BASF AG. We thank Prof. I . Erden for helpful discussions.

OEt

15 /EI-17/1ZI-i7

r n 1 0

18 19

Scheme 2. a) Tetrachlorocyclopropene, 155'C. 36 h. b) Zn/Cu, T H F / H 2 0 @/I), ultrasonication, 6 5 T , 20 h. c) C O ~ ( C O ) ~ , CO, 120"C, 48 h. d ) 600"C, 0.1 torr, 0.09 s. e) ( E ) : 125"C, (a: 135°C. f , E t 2 0 , 2 i i HCI, RT. g) 250"C, 0.02 torr, 0.8 s.

Cycloadditions to the triple bond of such alkynylcyclo- propanes afford vinylcyclopropanes[12] in which the vinyl group is incorporated into a ring and whose rearrangement to a cyclopentene should be facilitated by the 2-ethoxy or the 2-acetoxy function.

Thus reaction of (E/Z)-7a with cyclopentene 12 and C O ~ ( C O ) ~ under CO (cf. [ I 3 ' ) followed by chromatographic separation gave a 1 : 1.6 mixture (30%) of both diastereom- ers of 3-(2-ethoxycyclopropyl)-cis-bicyclo[3.3.0]oct-3-en-2-

770 0 VCH Verlagsgerellrchafr mhH, 0-6940 Weinheim, 1985 0570-0833/85/0909-0770 S 02.50/0 Anyew. Chern. Ini. Ed. Engl. 24 (19851 No. 9

one, ( E ) - 131"' with ( E ) configuration on the 3-membered ring and a 1 : 1 mixture (4Yo) of both diastereomers of (2)- 13. Reaction of pure (E)-7b with I-cyclopentenylpyrrolid- ine 15 at 125°C furnished the cycloheptadiene derivative (E)-16 (55%); ( 9 - 7 b was converted at 135°C into (2)-16 (47%). The enamines 16 can be hydrolyzed to the methyl 7-0x0-2-cycloheptene- 1 -carboxylates (E)- 17 (16%) and (9- 17 (37%),['] respectively.

Upon flash vacuum pyrolysis, 13 is smoothly converted into the linearly annelated triquinane 1416' (39% after chro- matography on SiO,).["I Product 14 consisted of three ster- eoisomers in a ratio of 4 : 2 : 1, whose separation thus far has been achieved only by capillary gas chromatography. According to 'H-, 'H,H-COSY- and 'H,"C-correlation- NMR spectra, the ratio of anti- and syn-configurated iso- mers is 5 : 2 or 3 :4. The cycloheptene derivative, (2)-17, rearranges especially easily; evidently the main reason for this is that the B-ketoester splits off methanol above 250"C, forming the ketoketene 18,['4~151 which, due to favorable stereochemistry, can cyclize with ethoxy-group migration to give ethyl 3-oxobicyclo[5.3.0]deca-1,9-diene-2-carboxy- late 19.

Received: October 16, 1984; [Z 1040 IE]

German version: Angew. Chem. 97 (1985) 763 revised: June 25, 1985

[I] Reviews: M. Ramaiah, Synthesis 1984. 529: R. F. C. Brown: Pvrolytic Methods in Organic Chemistry. Academic Press, New York 1980, p. 309 ff.

[2] Cf. B. M. Trost, P. H. Scudder, J. Org. Chem. 46 (1981) 506. [3] H. G. Richey, Jr., D. M. Shull, Tetrahedron Letf. 1976, 575. [4] a) W. Weber, A. d e Meijere, Angew. Chem. 92 (1980) 135; Angew. Chem.

Int. Ed. Enyl. 19 (1980) 138; b) W. Weber, A. d e Meijere, Chem. Ber. 118 (1985) 2450: c) W. Gothling, S. Keyaniyan, A. de Meijere, Tetrahedron Lett. 2.5 (1984) 4101.

[5] a) T. Liese, A. de Meijere. Angew. Chem. 94 (1982) 65; Angew. Chem. Int. Ed. Engl. 21 (1982) 65; Angew. Chem. Suppl. 1982, 34; b) T. Liese, G. Splettstosser, A. de Meijere, Tetrahedron Lett. 23 (1982) 3341.

[6] All new compounds were unequivocally characterized by their IR, 'H- NMR, and where necessary, "C-NMR spectra; in most cases satisfac- tory elemental analyses were obtained. Examples: 13: IR (film):

cm - I , 'H-NMR 1270 MHz, CDCI,): 6=0.90-1.00 (m, I H, 3'-H,,), 1.10- 1.20 (m, I H , 3'-Hh), 1.20 (t, 'J=7.0 Hz, 3 H , 2"-H), 1.50-1.95 (m, 7 H , 6,7,8,1'-H), 2.70-2.80 (m, I H, I-H), 3.10-3.20 (m, 1 H, 5-H), 3.25-3.35 (m. 1 H, 2'-H),3.48+3.59(q+mc,2H,int. ratio I : l .6, I"-H),6.74+6.77 (2d , I H, 'J=3.5 Hz, int. ratio 1.6: I , 4-H); MS (70 ev): m/z 206 ( M ' ) - 14: IR (film): v=3030-2850 (C-H), 1700 (C=O), 1620 (C=C), 1150- 1020 (C-0) cm- ' : 'H-NMR (400 MHz, C,D,): 6=0.83-2.00 (m, 6 H , 9,lO,Il-H), 1.04, 1.10, 1.13 (3t, ' J s 7 . 0 Hz,3H, int. ratio 1 : 2 : 4 , 2'- H), 2.00-2.40 (m, I H, 8-H), 2.40-2.70 (m, 3 H, 1.4-H), 2.64-3.32 (m, 3 H, 2,l'-H), 3.66, 3.72, 3.88 (3 mc, 1 H, int. ratio 1 :2:4, 3-H),6.01, 6.08, 6.17 (3mc. 1 H, int. ratio 2 : 4 : I, 5-H); MS (70 eV): m/z 206 ( M + ) - ( . Z - 1 7 : IR (film): v=3400 (0-H), 3030-2850 (C-H), 1640 (C=O), 1590 (C=C), 1240, 1030 ( G O ) c m - ' : 'H-NMR (270 MHz, C,D,): 6 ~ 0 . 6 1 (ddd,

(ddd. 'J( 1',3'2)=7.0 Hz, 'J(2',3'Z)=3.6 Hz, I H, 3'-H(Z)). 1.02 (X com- ponent of an ABX, system, './(AX)= ' J (HX)=7.0 Hz, 3 H, OCHICHI), 1.75 2.03 (m, SH, 5,6,I'-H), 2.25-2.58 (m, 2H, 4-H), 3.04 (ddd, 'J(1',2')=6.4 Hz, I H, 2'-H), 3.30 (AB component of an ABX, system, 2H, OCH,CH,), 3.36 (s, rel. int. 0.5, I-H), 3.37 (s, 3H) , 5.93 (mc, I H, 3- H), 7.44 (bs, rel. int. 0.5, enol-H).- 19: IR (film): v=3030-2830 (C-H), 1710. 1640 (C=O), 1600 (C=C), 1220, 1180, 1020 (C-0) c m - ' ; 'H- NMR (270 MHz, C,D,): 6=0.84 (mc, 1 H, 6-H,,), 0.96 (X component of an ABX, system, 'J(AX)='J(BX)=7.0 Hz, 3 H, 3'-H), 1.08-1.20 (m, 2H, 5-H,, h-H,,), 1.35 (mc, 1 H, 5-H,), 1.50 (dddd, 'J= - 19.2 Hz, 'J(Xa.7)= 1.8 Hz, 'J(8a,9)=2.2 Hr, 'J(Sa,I0)=2.8 Hz, I H, 8-H,,), 2.03- 2. I 8 (m, 2 H, 4-H,,, 8-H,), 2.27 (mc, 'J= - 15.2 Hz, 1 H, 4-Hb), 4.1 I (AB component of an ABXi system, 2 H , 2'-H), 5.96 (ddd, 'J(c;s)=5.5 Hz, JJ(10.Xa)='1J(10,8b)=2.8 Hz, I H, 10-H), 6.81 (ddd, 'J(B.Xn)='J(9,8b)=2.2 Hz, 9-H): MS (70 ev): m / z 220 ( M + ) , 151 (M-C'?H<)*.

[7] Simple heating of 2 with Zn/Cu couple in T H F / H 2 0 did not lead to re- duction as described for 7.7-dibromonorcardne (R. M. Blankenship, K. A. Burdett. J. S. Swenton, J. Org. Chem. 39 (1974) 230). The selective re- duction of 2 with Zn/Cu in a laboratory cleaning bath (Bandelin, Mod. R K 2 2 5 ) is a further example of the utilization of ultrasound-activated

~=3030-2850 (C-H), 1700 (C=O), 1630 (C=C), 1200-1020 (C-0)

'J=.SX Hz, 'J(1'.3'E)=9.6 Hz, 'J(2',3'E)=6.2 Hz, 1 H, 3'-H(E)), 0.70

zinc in organic synthesis (cf. B.-H. Han, P. Boudjouk, J . Ory. Chem. 47 (1982) 751, 5030).

[XI Similar reduction of ( a - 2 gave a I : I mixture of ( E ) - and (2)-3. [9] With the method described for other chloroacetylenes (LiN Et2, Et'O,

-78°C: J. Villieras, P. Perriot, J. F. Normant, Synthesis 1975. 458) the maximum yield of 6 was 56%.

[ lo] Based on the method of: E. V. Dehmlow, M. Lissel. Liebigs Ann. Chem. 1980, I ; Tetrahedron 37 (1981) 1653.

[ 1 I] Cf. L. Brandsma: Preparative Acetylenic Chemistry, Elsevier, Amsterdam 1971, p. 85; S. Y. Delavarenne, H. G. Viehe in H. G. Viehe (Ed.): Chem- istry of Acetylenes, Marcel Dekker, New York 1969.

[I21 G. Splettstosser, S. Keyaniyan, A. de Meijere, unpublished results: G. Splettstosser, Disserfatron. Universitat Hamburg 1985.

[ 131 Analogously synthesized compounds of type 13 without electron-donat- ing substituents required up to 150°C higher pyrolysis temperatures un- der otherwise identical conditions; J . P. Richmond, T. Liese, A. de Mei- jere, unpublished results.

[I41 Cf. C. Wentrup, K.-P. Netsch, Angew. Chem. 96 (1984) 792; Angew. Chem. In t . Ed. Engl. 23 (1984) 802.

[I51 a-Ketoketenes of type 18 were detected in the pyrolysis of 17-analogues without the ethoxy substituent (cf. [ 121).

Heterogeneous Redox Catalysis on Ti/Ti02 Cathodes-Reduction of Nitrobenzene** By Fritz Beck* and Wolfgang Gabriel

Reductions with low valency titanium compounds are well known in organic chemistry. Typical examples are, inter alia, the reduction of nitro compounds with and the reductive dimerization of ketones to olefins with

Stoichiometric quantities of reducing agent were used in these reactions. The selectivity of the processes is explained in terms of a complexation of the reactants with the titanium species. Since large amounts of reagents such as TiCI, are not easy to handle, it was suggested that the reduction be carried out on an inert cathode in the pres- ence of a dissolved redox mediator such as (TiO)S0414'11 or TiC14.[4b1 We report herein on a further simplification, namely the oxidic Ti-redox system fixed to the surface of a Ti cathode.

The Ti/Ti02 electrode was fabricated using a method employed in the production of ceramic^.^"^ As shown by the cyclic voltammograms la, b in Figure 1, reduction of the surface layer starts at ca. UH = - 0.1 V with respect to a standard hydrogen electrode. This corresponds to the equilibrium potential for Reaction (a):["

(a) Ti(OH), + e0 + He ------) Ti(OH), + H,O

At more negative potentials, further reduction processes come into operation, with a current maximum at UH = - 0.73 V and a shoulder at UH = - 0.65 V. Whether

transitions, e.g. Reaction (b), Ti1v/Ill

TiOz + HZO + H@ + e0 - Ti(OH),, UH.o= -0.79 V (b)

redox processes operate,@' both of which are pos- sible in this voltage range, cannot be decided with certain- ty. At still more negative potentials, cathodic evolution of hydrogen begins to take place (Fig. I , 8). The correspond- ing re-oxidation processes are detected cyclovoltammetri- cally. The Ti02 layer is converted up to 2-20%, a relatively high value for a solid-state reaction, the conversion de- creasing with increasing voltage scan rate. The redox proc- esses can be repeated as often as desired. At higher pH val-

or Til11/11

[*I Prof. Dr. F. Beck, DipLChem. W. Gabriel FB 6- Elektrochemie der Universitat-Gesamthochschule D-4100 Duisburg 1 (FRG)

[**I This work was supported by the Deutsche Forschungsgemeinschaft

Angew. Chem. Int. Ed. Engl. 24 (1985) No. 9 0 VCH Verlagsgesellschaft mbH. 0-6940 Weinhelm. 1985 OJ70-0833/85/1)909-0771 $ 02.50/0 71 1