Organometallics 1993,12, 656-662
656
(Cyclobutadiene)tricarbonyliron Complexes: Formation of 1,3- and 1,2,3-Substituted Derivatives' Christopher M. Adams,' Scott A. Joslin,2 Ellen S. Crawford, and John E. Schemenaur Department of Chemistry, Oklahoma State University, Stillwater, Oklahoma 74078-0447 Received July 15, 1992 Current methods available to modify or append alkyl groups to (cyc1obutadiene)tricbonyliron limit its use and study. Using selective alkylations and rearrangements on diisopropyl squarate, we have developed simple and efficient routes to specific 1,3-disubstituted (2) and 1,2,3trisubstituted (3) (cyc1obutadiene)tricarbonyliron complexes. These methods represent the first direct syntheses of these complexes and provide new entries into potentially novel cyclobutadiene-derived synthons and complexes.
Introduction The paucity of methods to synthesize specific 1,2-, 1,3-, and 1,2,bsubstituted cyclobutadiene complexes 1,2, and 3, respectively, limit their study and potential application as synthons in organicchemistry (Chart I). The syntheses of the few known 1,3-disubstituted (cyc1obutadiene)tricarbonyliron complexes involve many steps from the parent cyclobutadiene complex 4. Examples of these complexes include ([2.2]-1,3-cyclobutadienophane)bis(tricarbonyliron) (5) 13 [(1,8,9,lO-v)bicyclo[6.1.1I -decal(10),8-dien-2-one]tricarbonyliron (6) ,4 (1,3-di-tert-butylcyc1obutadiene)tricarbonyliron (7),5 and (l-acetyl-3ethylcyc1obutadiene)tricarbonyliron (8Is6Free cyclobutadiene can be generated from the parent (cyclobutadiene)tricarbonyliron by oxidation.' The extremely reactive cyclobutadieneparticipates as a Diels-Alderpartner7 and in this manner has been used in the construction of strained caged compounds,for example,cubane6and caged keto-sulfides? Early methods to synthesize disubstituted cyclobutadiene complexes have involved thermal and photochemical reactions to product suitably substituted, 4-membered ring precursors. Notable examples of these reactions are the 12 + 21 thermal cycloadditions of perhaloethylenes with alkylacetylenes1°and dibromomaleic anhydride,ll and [2 + 21 photochemicalcycloaddition ~~
(1) Preliminary work was presented in part at the 203rd ACS National Meeting, San Francisco, CA, April 5-10, 1992, Division of Organic Chemistry, Abstract No. 305. (2) Summer 1990 recipient of Project SEED Fellowship, Petroleum Research Fund, American Chemical Society. (3) Adams, C. M.; Holt, E. M. Organometallics 1990, 9, 980-986. (4) Adams, C. M.; Crawford, E. S.; Salim, E. Tetrahedron Lett. 1992, 33,3963-3966. (5) Reeves, P.;Henery, J.; Pettit, R. J.Am. Chem. SOC.1969,91,588& 5890. (6) Marcinal, P.; Hannoir-Guisez, N.; Cuingnet, E. Trau. SOC.Pharm. Mont. 1973, 33, 281-288. (7) (a) Efraty, A. Chem. Reu. 1977, 77, 691-743 and references cited therein. (b) Watts, L., Fitzpatrick, J. D.; Pettit, R. J. Am. Chem. SOC. 1965, 87, 3253-3254. (c) Emerson, G. F.; Watts, L.; Pettit, R. J. Am. Chem. SOC.1965,87, 131-133. (8) Barborak, J. C.; Watts, J. C.; Pettit, R. J. Am. Chem. SOC.1966, 88,1328-1329. (9) Paquette, L. A.; Wise, L. D. J.Am. Chem. SOC.1967,89,6659-6666. (10) (a) Smutny, E. J.;Caserio, M. C.;Roberts, J. D. J.Am. Chem. SOC. 1960, 82, 1793-1801. (b) Brune, H. A.; Hanebeck, H.; Htther, H. Tetrahedron 1970,26,3099-3112. (c) Bloomquist, A. T.; LaLancette, E. A. J. Org. Chem. 1964,29, 2331-2334. (11) ( E ) Berens, G.; Kaplan,F.; Rimerman,R.; Roberta, B.W.; Wissner, A. J. Am. Chem. SOC.1975,97,7076-7085. (b) Roberts, B. W.; Wissner, A.; Rimerman, R. A. J. Am. Chem. SOC.1969,91, 62084209.
0276-733319312312-0656$04.OOf0
of vinylene carbonate with alkylacetylenes.12 The regioselectivity of these reactions generally leads to 1,2disubstituted products as components of complex mixtures. Such reactions are often plagued with undesired dimerizations, low yields, and difficulties with product isolation? We recently reported new syntheses of 1,2disubstituted (cyc1obutadiene)tricarbonyliron complexes;13however, the 1,3-regioisomersdo not lend themselves to facile synthesis through established thermal or photochemical reactions.
Results and Discussion Our synthetic requirements for new, more desirable, and rare l,&disubstituted cyclobutadienecompleses2 led us to investigate modifications of our reported 1,2disubstituted cyclobutadienecomplexsyntheses based on diisopropyl squarate (9).13 A retrosynthetic analysis for the preparation of 1,&disubstituted cyclobutadienemetal complexes is shown in Scheme I. Selective Grignard additions, selective hydrolyses, and selective carbonyl reductions are used to furnish the 1,3-substitutionpattern in the sequence. A number of groups have reviewed the history and syntheses of substituted cyclobutenedionesfrom squaric ester^.^"'^ We sought to utilize and extend our facile preparative methodology for 1,2-disubstituted (cyclo(12) (a) Grubbs, R. H. J. Am. Chem. SOC. 1970,92,6693. (b) Grubb, R. H.; Pancoast, T. A.; Grey, R. A. Tetrahedron Lett. 1974,2425-2426. (c) Grubbs, R. H.; Grey, R. A. J. Chem. SOC.,Chem. Commun. 1973, 76-77. (13) Adams, C. M.; Schemenaur, J. E.; Crawford, E. S.; Joelin, S. A. Synth. Commun. 1992,22 (lo), 1385-1396. (14) (a) Liebeskind, L. S.; Fengel, R. W.; Wirtz, K.R.; Shawe, T. T. J.Og.Chem. 1988,53,2482-2488. (b) Liebeskind, L. S.;Baysdon, S. L. Tetrahedron Lett. 1984, 25,1747-1750. (15) Reed, M. W.; Pollart, D. J.; Perri, S.T.; Foland, L. D.; Moore, H. W. J. Org. Chem. 1988,53,2477-2402. (16) For general reviews on the properties and the preparation of cyclobutanediones and squaric esters see: (a) Cava, M. P., Mitchel, M. J., Eds. Cyclobutadiene and Related Compounds;Academic Press: New York, 1967; Vol. 10 and references cited therein. (b) Schmidt, A. H.; Ried, W. Synthesis, 1978,l-22. (c) Knorr, H.; Ried, W. Synthesis 1978, 649-666. (d) Schmidt, A. H.; Ried, W. Synthesis 1978, 869-880. (e) Martin, H.-D.; Oftring, A,; Iden, R. Tetrahedron Lett. 1982,23,841-844. (0 Dehmlow, E. V.; Schell, H. G. Chem. Ber. 1980,113,l-8. (g) Kraut, J. L. TetrahedronLett. 1985,26,1867-1870. (h) Paine, A. J. Tetrahedron Lett. 1984,25, 135-138. (i) Chickos, J. C. J. Am. Chem. SOC. 1970,92, 5749-5750. fi) See ref 14. (17) Krysan, D. J.; Curski, A.; Liebeskind, L. S.J. Am. Chem. SOC. 1992,114, 1412-1418.
0 1993 American Chemical Society
(Cyc1obutadiene)tricarbonylironComplexes
Organometallics, Vol. 12, No. 3, 1993 667
Chart I
co co.~e....*lco R'
co/~**.,,co co 1: R',R3 alkyl; Rz = H 2: R1,RZ = alkyl; R3 = H 3: R1,R2,R3 = alkyl 4: R1,RZ,R3= H
co'
X = OH, OR, halogen,
or another leaving group
w
"
'
5
\ c p
Scheme I
O
6
--
Pe
7
2
eo
O w 0
