The Preparation of Furoin-A
Biomimetic Reaction
R. W. Hanson Department of Biological Sciences, University of Plymouth. Plymouth, Devon U.K.
stirred ethanolic solution of the reactants and catalvst and Thiamine ~ v r o ~ h o s ~ h(TPP. a t e 1. R' = 4-amino-2methylpyrimi%n-&l, R' = CH3, R' = ' - C H ~ C H ~ O P ~ O ~ H ~is) sufficiently pure for most practical purposes witGout recrvstallization. When prepared on the scale described here is an essential cofador for enzvmes that catalvze the decarboxylation of u-keto acids a i d related acyl&-forming thk yield of furoin is tipically 8 5 9 or more; slightly lower .yields I-80G1 are obtained starting from 20 mmol of furfureactions ( 1 1 . Cyanide ions catalvze the same reactions in ;ul. In hoth cases the yield is m a s n a l l y depressed, and a a mechanisti~afl~ similarmanneirl~and consequently the well-documentedc.yanidecatalyzed preparationof benzoin slightly discolored product is obta~nedif the reaction mix(2)could be used in undergraduate iabbratories to illustrt&e is-not stirred. ate the role of TPP. Cyanide, however, is neither an ideal reagent for use by undergraduates nor an obvious strucExperimental Directions tural analogue of TPP; the use of the coenzyme itself, or a nontoxic close analogue of it, would be desirable. Ault (3) The catalyst can be purchased from the Aldrich Chemihas described the use of thiamine hydrochloride in the cal Co. or prepared as described by Stetter and Kuhlmam (.5) Dresence of aoueous sodium hvdroxide solution to catalvze . .Triethvlamine should be dried over solid notassium hvthe formation' of benzoin from benzaldehyde. The expkridroxide akd distilled; furan-&aldehyde (fukural) shouid ence of the author. however. is that this preparation is unbe distilled immediatelv before use. reliable, possibly'due to the occurrence df a competing Cannizzaro reaction. Furoin In contrast, Stetter's (4) method of acyloin formation Dissolve the catalyst (1.34 g, 5 mrnol) and furfural (9.61 involving the use of dry ethanol as solvent and 3-benzylg, 8.3 mL, 100 mmol) in absolute ethanol (30 mL). Add tri5-(2-hydroxyethyl)4-methyl-1,3-thiazolium chloride (1,R1 ethylamine (3.03 g, 4.2 mL, 30 mmol) and magnetically = Ph, R2 = CHR.R3 = -CH&H20H) in the presence of tristir, in a closed flask, the deep cherryred solution that reethylamme as the catalysthn~beenfoundto be very relisults. The product starts to separate after approximately able. Unlike cyanide, the catalyst is not known to be tox~c 15 min. ARer 18 h, cool the mixture in ice, collect the prodand is a close analogue of TPP, and its use, in particular, in uct on a filter, and wash it first with 3 x 10-mL portions of 2) (5) the production of furoin (2-furoyl-2-furylcarhinol, ice-cold ethanol and then with 3 x 10-mL portions of cold nmvides an excellent biomimetic acvloin-formine reaction .LL.eulel: tor undergraduates. The product, khich also appears to The yield of furoin, with mp = 136-137 'C (lit. mp = 13% be nontoxic, separates rapidly a t mom temperature from a 136 T,6) is typically more than 8.16 g (85%).IR (KBr): OH 3420, 3360 (4; C=O 1680(s) cm-I. MS: mle 192 (M', 12), 97(100), 95(72). Literature Cited 1. Hanson, R. W. J. Chem Edue. 1987, €4,591-595, 2. Tietee,IrF: Eieher. T. Reactions a d Syntksiein fkOrganic C k m i s t q h b o r o f o r y , Univemitt kience: MillVallev. C A 1989: o 187. ton,1983;p 459.
4. Stetter, H.:Rarnsch, R. Y.; Kuhlrnann, H. Syntksis Is?%, 733135. 5. Stetter,H.: Kuhlrnann, H. O g Synth. C d l . Vd. VII 1990.97. 6. Vogel. A. I. V w l s Tkdbmk of Pmcflml Organic Chemistry, 5UI ed.: Ian-": low 1989;p 1044
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