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Dichloromethane as a source of the CH22-synthon: A combination of an arene-catalysed lithiation and a barbier-type reaction
akin
urns
are oues of the most powerful Iqjents iu synthetic orgauic Bernie
in C.&on-carbon bond forma&m processes by reaction with el~~~iiic
above all
reagentst. Among these type of
intermedktes the cosmsponding gemin& diMhium compound42 arevery rare and uustabie speciea F+ imtatse, the preparation of ~ii~orne~~.~, rn~y~~~
or (b) by rn~~-Ii~~
the simplest g~~li~~, ~e~~a~~6.
has been carried out (a) by pyrolysis of Tk direct regiment
of cogs
(~i~7
or
chlorin&) with lithium, the most useful methcd for the syuthe& of organofithium impounds, ie not applicable, in gene&, to the syntbesiisof g~li~~ step giving a a,
being this m
~v~to~~e~~u~~c~t~~~
moleeuies due to the a-eliminatiou of lithium halide after the first fas&r than the ssond 1ithiationW On the other band, we have recently with lithium powder allows tbt? very mild reactiou comiitions.
This procedure works uioely not only for c~~~-li~urn
ex&u~gelZ but ala0 in other ~i~ati~
ptxxmmsl3.
The reoent report of Klumpp 62aI. on redt~tiou of gemiual~~~clo~~~ with lithium 4,4-d&&M~~lbi~enyl p~rnp~ us to Ernst in this paper our ~~~~ on the ~ne-~~~ dili~iatio~ of ~~~~ and ~~g~c~~ de&atives in a Bar&r-type re@ion. The reaction of di~~~~e 1 with an tcwx+as of lithium powder (I:7 molar ratio) aud a WaIytic amount of 4,~~i-&~-bu~l~~~yl(S mol %) in the presem~ of a carbony compound 2 (1:2 molar ratio) in tetrahydrofman at -4WC led, after hydrolysis, to the cormsponding I,Miols 3 (Scheme 1 and Table 1). In the csz.e of using an aidehyde as the mbonylic component the correqonding diastessisomeric mixture was sepamted by f&h chewy and e& ~~~~ analysed by 300 MHz 1H NMR in order to assign 253
254
the corresponding stereochemistry (Table 1, entries l-3). All reactions gave a small amount (tlS%) corresponchng pinacdine-type
of the
compounds 4, except in the case of using isopentanal in which a 3 1% of pinacol
was isolated; separation of compounds 3 aud 4 was carried out by careful flash chromatography. cyclopentanone w cyclohexanone were used as carbonyl substrates I-methyk+x&mes
When
Sa, were detected by
GIX in 15 and 25% yield, respectively (Table 1, entries 4 and 5).
0 cH&
+
A R2 R’
2
1
i,ii Jx
-
R2
2
R2R’
3
Scheme 1. Reagents and condQ&urs:i, Li powder (1:7 molar ratio), 4,4’-di-&rt-butylbiphenyl cat. (5 md %), THF, -4ooC; ii, H@.
HoR’ R’
h R2
R’
OH
4
Tabk 1. Preparation of 1,3-Dials 3
-pouad
-9 Entry
R’
F??
Product 3a no.
yield (%)b untihyn ratioc [m,p.(“C)]d
8HcsclWCCW.W
aniifsyn 1
H
pri
3a
52
5 WI/2
2
H
Bui
3b
35
3 [ill-112]/2
3
H
But
3e
61
[oil]
3 [149-151]/2 [98-1011
4
-w-w4-
3d
27
5
-W-W-
3e
25 (zry
aAll
[oil]
WV
1.60(36.35]/1.41.1.59 1.58[43.3]/1.43, 1.42[32.6]/1.27,
[35.85j
1.46[44.0] 1.72[30.95]
c-1
1.94[48.8]
[loo-1011
1.65[49.95]
isolated compounds 3 were z-95% pure (GLC and 300 MHz IH NMR) and were fully chamcterised by spectroscopic methods (IR, rH and r3C NMR, and MS}. b Isolated yield of pure compounds after flash ratio deduced after i&a&n of each ch~~g~~y (silica gel, hex~~ethy1 acetate). c ~~~~oi~rne~ component by flash chromatography; the stereochemistry was deduced from 300 MHz 1H NMR data. 4 From chloroform. (1In deuteriochloroform. f GLC yield of the corresponding I-methylcyclosJk 5d,e.
255
Fnmr a mechanistic
point of view we think that after the first lithiatioa a carbenoide of the type f is
obtainedt~, which in the psence
of the carbonyl compound 2 undergoes mainly a rapid co&en&on
of the corresponding a-elimination
(instead
reaction) to give a chlotohydrine salt of the type II19 The further lithiation
of the intermediate II affords a very reactive +Ikoxidc
aide
species NW, which in the presence of
the electrophile yields the dialkoxide IV and. after hydrolysis, the obtained products 3. The tmnsfonnation IIINV
is a crucial step due to the great instability of intermediate III: in absence of the electrophile
it
decomposes even at -WY! to give either proton abstractionls (yielding compounds of the type 5) or $elimination of lithium oxide (giving an defin)lg. The extreme instability of the species I and III can explain the modest yields in the obtained 1,Sdiols 3 (Table 1).
,?’
Li <
cl
t
I
(-JJ
Ll III
In order to extend the methodology here described we tried preliminary the same process using other gemdichioro derivatives. Thus, using the starting material @and pivslaldehyde, a mixture of compounds 7 (25%; cu. 2: I diastereoisomer mixture) and 8 (37%; ea. 3:l diaster&somer mixture) was obtained in 62% global yield. As expected, substihztion on the carbanionic center makes it more unstable.
6
Finally we applied the ssme reaction to commercially available methyl dichloromethyl ether 9. which ~~~~~~~~~~~ ~~~ti~#~e~ce~~~~~~~~ 10 (10~3: 1 ratio) was isolated in 41% yield. OHOH
MeOCHC12 9
J+bfvleal’
But
10
From the results described in this communication we conclude that dichloromethane can be used as a source of the synthon CH$- in a Etarbier-type reaction with cat-bony1 conrpounds. This methodology applied to other gem-dichbro methoddogy-
can be
derivatives; studies are in due coume in order to staMish the scope of this
256
In a typkeal reaction to a blue suspension butylbiphenyl(26
of lithium powder (cu. 100 mg, 14 mmol) and 4,4’di-k?rt-
mg, 0.1 nunof, 5 mof %) in THF (5 ml) was slowly added a solution of dicbloromethane
mmol) and the corrqo&ng addition the corresponding
carbcnyl compcund
(4 mmol) in THF (5 ml) during CLL. 45 min at -40X
mixture was stirred for 10 additional
min at the same temperature.
(2
After the
Then it was
hydrdlysed with water (4 ml), neutmliscd with 2 N hydrochloric acid and extracted with diethyl ether (2x10 ml). The organic layer was dried with anhydrous puriSed by flash chromatography
Na#Q
and evaporated (15 Tot-r). The resulting
residue was
(silica gel, hexaneZethy1 acetate) to give the expected products 321.
References and Notes 1. Wakefield, B. J. Qr@zno~ M&u&; Academic Presix London 19BB. For a review. see: Maercker. A.: Theis. M. TOO.Cum, Chem. lWn, 138.161. 32: For a recent study on the structure of diiithio&?thane, see: St&y. ci. D.;‘Eddy, M M.; Harrison, W. H.; Lagow, R; Kawa H.; Cox. D. E. J. Am. Ckm. Sot. 1990,1Z2,2425-2427. 4. For theoretical studies on dilirhiomethane see, for ins(a) Collins, J. 3.; Dill, J. D.; Jemmis, E. D.; Apeloig, Y.; Schleyer, P. v. R; Sager, R; Pople, J. A. J. Am. Glum. Sot. 1976,98. 54195427. (b) Nilssen, E W.: Skancke, A. J. Urganomer. Chem 1976,116,251-256. (c) Laidig. W. D.; Schaefer III, H. F. J. Am. C~FJL Sot. 1978, ZOO,5972-5973. (d) Jemmis, E D.; Schleyer, P. v. R; Pople, J. A. J. Or ~~~. Clrenr.1978,154,327-335. (e) Bachrach, S. M; Streihviaer, Jr., A. J. Am. Chem. Sot;= 19L , Z06,5819-!5824. (f) Ahmxio-Swaisgood, A. E; Harrison, J. F. J. E’fqs. Ckem. 1985, &9,6267. 5. (a) Ziegler, K.; Nagef, K.; Patheiger, M. Z. Amrg. Aug. Cirent. 1955,282,345-351. (b) Shimp, I, A.; Morrison, J. A.; Gurah, J. A.; Chinn. Jr.. J. W.; Lagow, R J. J. Am. Chem. Sot. 1981, Z03,59515953. (c) Gurak, J. A.; Chinn, Jr., J. W.; Lagow, R J. J. Am. Chem. Soc.1982, 104. 2637-2639. 6. Maercker. A.: Theis, M; Kos, A. J.; Schleyer, P. v. R Artgew. Chem. Znt. Ed. Engl. 1983, 22,733735. 7. West, R; Rochow. E. G. J. otg. Chem. 1953.Z8, 1739-1742, Baran, Jr., J. R; Lagow, R J. J. Am. Chem. Sec. 1990,112, 94159416. f: See reference 5 p. 21-22. 10: Yus. M.; Ram&r, D. J. J. Chem. Sot., Ckem. Commun. 19P1,3!&400. 11. For a review on functionahsed organolithium compounds, see: Najera, C.; Yus, M. De&s in Orgunic Ciwndy 1991,2, 155181. 12. (a) Yus, M.; Ran& D. J. .Z. Org. Client. 1992, 57,7SO-751. (b) Ramon, D. J.; Yus. M. Tem&edmz Lea. 1992, 33,2217-2220. (c) Guijarro, A.; Ram&, D. J.; Yus, M. Te&~~ 1993.49, 4c59-482. (d) Guijarro, A.; Yus, M. Tetrahehn Len. lPP3,34,201 I-2014. (e) Gknez. C.; Ram&t, D. J.; Yus, M. Tetrahedron 1993,49,4117-4126. (f) Gil, J. F.; Ram&, D, J.; Yus, M. Tetru~dro~ 1993,#9, 4923-4938. (g) Guijarro, A:; Yus, M. Tetrahedron Len. 1993,34,34&74390. (h) Ram&t, D. J.; Yus, M. Tetrdedron, in press. (1) Ram6n. D. J.; Y us, M. Tetr&?dron Len, in press. 13. (a) Ram&r, D. J.; Yus, M. Ten&e&on 1992,48.35&5-X%8. (b) Guijarro, D.; Man&&, B.; Yus, M. Tetruhedron 1992,48. 4!593-4600. (c) Gui’arro. D. ; Mancheiio, B. ; Yus, M. Tc@&d~~n Lea. 1992, 33,5597-5600. (d) Almena, J.; Foubelo, d .; Yus, h4. Tetrahedron L.&t. 1993, 34, 1649-1652. (e) Guijarro, D.: ManchefSo, B.; Yus, M. Tebvzhedron 1993.49. 1327-1334. (I) Guijarro. D.; Yus, M. Tetruhedron 1993,49,7761-7768. (g) Gil, J. F.; Ram&t. D. J.; Yus. M. Tetruhertron, in press. Vlaar, C. P.; Wumpp, G. W. Angew. Ch.em. In?. Ed. Engl. lPP3,32,5’74-576. For a review, see: Siegel, H. Top. Cwr. Chem. 1982,Z&5, B-78. :; 16: This type of intermediates, obtained by direct deprotonation of chlorohydrins. are stable at low temperatures (no epoxides are obtained after hydrolysis): Bariuenga, J.; F&&z, J.; Yus, M. J. Chem. tic.. Chem. Cormrnur. 19g2, 1153-1154. 17. &Reagents (Seebach, D. Angew. C&m. Iti. Ed. Engi. 1979, 28.239258) of this type have been prepared at low temperanne by (a) rn~~-~~~ ~me~lati~: Barhtenga, J.: Faftan&, E J.; Yus, M.; Asensio, G. ~e~u~~~~ Left. r978, 20152016. (b) Chlorine-lithium exchange: Batiuenga, 1.; FhSrez, F.; Yus. M. J. Chem. Sot., Perkin Trans. Z 1983, 3019-3026. (c) reductive opening of epoxidesz Bartmann, E. &gew. Chem. Zar. Ed. Z?agZ.1986,2.5,653-654. 18. Bates, R. B.; Kropo&, L. M.; Potter, D. E. J. Org. Chem. 1972,37, 560-562. Barluenga, J.; Yus, M.; Bernad, P. J. Gem. Sot., Chem. C~un. 1978.847. 1:: parham, W. E.; Schweizer, E. E Organic Reuc2ion.r; John Wiley and Sons, Inc.: New Yorlc, 1979: vol. 13, ch 2, pp. 74-75. 21. This work was finnacially supported by DGICYT (PB91-0751) from the Ministetio de Educacibn y Ciencia (MEC) of Spain. A. 0. thanks the MEC for a grant
urns
are oues of the most powerful Iqjents iu synthetic orgauic Bernie
in C.&on-carbon bond forma&m processes by reaction with el~~~iiic
above all
reagentst. Among these type of
intermedktes the cosmsponding gemin& diMhium compound42 arevery rare and uustabie speciea F+ imtatse, the preparation of ~ii~orne~~.~, rn~y~~~
or (b) by rn~~-Ii~~
the simplest g~~li~~, ~e~~a~~6.
has been carried out (a) by pyrolysis of Tk direct regiment
of cogs
(~i~7
or
chlorin&) with lithium, the most useful methcd for the syuthe& of organofithium impounds, ie not applicable, in gene&, to the syntbesiisof g~li~~ step giving a a,
being this m
~v~to~~e~~u~~c~t~~~
moleeuies due to the a-eliminatiou of lithium halide after the first fas&r than the ssond 1ithiationW On the other band, we have recently with lithium powder allows tbt? very mild reactiou comiitions.
This procedure works uioely not only for c~~~-li~urn
ex&u~gelZ but ala0 in other ~i~ati~
ptxxmmsl3.
The reoent report of Klumpp 62aI. on redt~tiou of gemiual~~~clo~~~ with lithium 4,4-d&&M~~lbi~enyl p~rnp~ us to Ernst in this paper our ~~~~ on the ~ne-~~~ dili~iatio~ of ~~~~ and ~~g~c~~ de&atives in a Bar&r-type re@ion. The reaction of di~~~~e 1 with an tcwx+as of lithium powder (I:7 molar ratio) aud a WaIytic amount of 4,~~i-&~-bu~l~~~yl(S mol %) in the presem~ of a carbony compound 2 (1:2 molar ratio) in tetrahydrofman at -4WC led, after hydrolysis, to the cormsponding I,Miols 3 (Scheme 1 and Table 1). In the csz.e of using an aidehyde as the mbonylic component the correqonding diastessisomeric mixture was sepamted by f&h chewy and e& ~~~~ analysed by 300 MHz 1H NMR in order to assign 253
254
the corresponding stereochemistry (Table 1, entries l-3). All reactions gave a small amount (tlS%) corresponchng pinacdine-type
of the
compounds 4, except in the case of using isopentanal in which a 3 1% of pinacol
was isolated; separation of compounds 3 aud 4 was carried out by careful flash chromatography. cyclopentanone w cyclohexanone were used as carbonyl substrates I-methyk+x&mes
When
Sa, were detected by
GIX in 15 and 25% yield, respectively (Table 1, entries 4 and 5).
0 cH&
+
A R2 R’
2
1
i,ii Jx
-
R2
2
R2R’
3
Scheme 1. Reagents and condQ&urs:i, Li powder (1:7 molar ratio), 4,4’-di-&rt-butylbiphenyl cat. (5 md %), THF, -4ooC; ii, H@.
HoR’ R’
h R2
R’
OH
4
Tabk 1. Preparation of 1,3-Dials 3
-pouad
-9 Entry
R’
F??
Product 3a no.
yield (%)b untihyn ratioc [m,p.(“C)]d
8HcsclWCCW.W
aniifsyn 1
H
pri
3a
52
5 WI/2
2
H
Bui
3b
35
3 [ill-112]/2
3
H
But
3e
61
[oil]
3 [149-151]/2 [98-1011
4
-w-w4-
3d
27
5
-W-W-
3e
25 (zry
aAll
[oil]
WV
1.60(36.35]/1.41.1.59 1.58[43.3]/1.43, 1.42[32.6]/1.27,
[35.85j
1.46[44.0] 1.72[30.95]
c-1
1.94[48.8]
[loo-1011
1.65[49.95]
isolated compounds 3 were z-95% pure (GLC and 300 MHz IH NMR) and were fully chamcterised by spectroscopic methods (IR, rH and r3C NMR, and MS}. b Isolated yield of pure compounds after flash ratio deduced after i&a&n of each ch~~g~~y (silica gel, hex~~ethy1 acetate). c ~~~~oi~rne~ component by flash chromatography; the stereochemistry was deduced from 300 MHz 1H NMR data. 4 From chloroform. (1In deuteriochloroform. f GLC yield of the corresponding I-methylcyclosJk 5d,e.
255
Fnmr a mechanistic
point of view we think that after the first lithiatioa a carbenoide of the type f is
obtainedt~, which in the psence
of the carbonyl compound 2 undergoes mainly a rapid co&en&on
of the corresponding a-elimination
(instead
reaction) to give a chlotohydrine salt of the type II19 The further lithiation
of the intermediate II affords a very reactive +Ikoxidc
aide
species NW, which in the presence of
the electrophile yields the dialkoxide IV and. after hydrolysis, the obtained products 3. The tmnsfonnation IIINV
is a crucial step due to the great instability of intermediate III: in absence of the electrophile
it
decomposes even at -WY! to give either proton abstractionls (yielding compounds of the type 5) or $elimination of lithium oxide (giving an defin)lg. The extreme instability of the species I and III can explain the modest yields in the obtained 1,Sdiols 3 (Table 1).
,?’
Li <
cl
t
I
(-JJ
Ll III
In order to extend the methodology here described we tried preliminary the same process using other gemdichioro derivatives. Thus, using the starting material @and pivslaldehyde, a mixture of compounds 7 (25%; cu. 2: I diastereoisomer mixture) and 8 (37%; ea. 3:l diaster&somer mixture) was obtained in 62% global yield. As expected, substihztion on the carbanionic center makes it more unstable.
6
Finally we applied the ssme reaction to commercially available methyl dichloromethyl ether 9. which ~~~~~~~~~~~ ~~~ti~#~e~ce~~~~~~~~ 10 (10~3: 1 ratio) was isolated in 41% yield. OHOH
MeOCHC12 9
J+bfvleal’
But
10
From the results described in this communication we conclude that dichloromethane can be used as a source of the synthon CH$- in a Etarbier-type reaction with cat-bony1 conrpounds. This methodology applied to other gem-dichbro methoddogy-
can be
derivatives; studies are in due coume in order to staMish the scope of this
256
In a typkeal reaction to a blue suspension butylbiphenyl(26
of lithium powder (cu. 100 mg, 14 mmol) and 4,4’di-k?rt-
mg, 0.1 nunof, 5 mof %) in THF (5 ml) was slowly added a solution of dicbloromethane
mmol) and the corrqo&ng addition the corresponding
carbcnyl compcund
(4 mmol) in THF (5 ml) during CLL. 45 min at -40X
mixture was stirred for 10 additional
min at the same temperature.
(2
After the
Then it was
hydrdlysed with water (4 ml), neutmliscd with 2 N hydrochloric acid and extracted with diethyl ether (2x10 ml). The organic layer was dried with anhydrous puriSed by flash chromatography
Na#Q
and evaporated (15 Tot-r). The resulting
residue was
(silica gel, hexaneZethy1 acetate) to give the expected products 321.
References and Notes 1. Wakefield, B. J. Qr@zno~ M&u&; Academic Presix London 19BB. For a review. see: Maercker. A.: Theis. M. TOO.Cum, Chem. lWn, 138.161. 32: For a recent study on the structure of diiithio&?thane, see: St&y. ci. D.;‘Eddy, M M.; Harrison, W. H.; Lagow, R; Kawa H.; Cox. D. E. J. Am. Ckm. Sot. 1990,1Z2,2425-2427. 4. For theoretical studies on dilirhiomethane see, for ins(a) Collins, J. 3.; Dill, J. D.; Jemmis, E. D.; Apeloig, Y.; Schleyer, P. v. R; Sager, R; Pople, J. A. J. Am. Glum. Sot. 1976,98. 54195427. (b) Nilssen, E W.: Skancke, A. J. Urganomer. Chem 1976,116,251-256. (c) Laidig. W. D.; Schaefer III, H. F. J. Am. C~FJL Sot. 1978, ZOO,5972-5973. (d) Jemmis, E D.; Schleyer, P. v. R; Pople, J. A. J. Or ~~~. Clrenr.1978,154,327-335. (e) Bachrach, S. M; Streihviaer, Jr., A. J. Am. Chem. Sot;= 19L , Z06,5819-!5824. (f) Ahmxio-Swaisgood, A. E; Harrison, J. F. J. E’fqs. Ckem. 1985, &9,6267. 5. (a) Ziegler, K.; Nagef, K.; Patheiger, M. Z. Amrg. Aug. Cirent. 1955,282,345-351. (b) Shimp, I, A.; Morrison, J. A.; Gurah, J. A.; Chinn. Jr.. J. W.; Lagow, R J. J. Am. Chem. Sot. 1981, Z03,59515953. (c) Gurak, J. A.; Chinn, Jr., J. W.; Lagow, R J. J. Am. Chem. Soc.1982, 104. 2637-2639. 6. Maercker. A.: Theis, M; Kos, A. J.; Schleyer, P. v. R Artgew. Chem. Znt. Ed. Engl. 1983, 22,733735. 7. West, R; Rochow. E. G. J. otg. Chem. 1953.Z8, 1739-1742, Baran, Jr., J. R; Lagow, R J. J. Am. Chem. Sec. 1990,112, 94159416. f: See reference 5 p. 21-22. 10: Yus. M.; Ram&r, D. J. J. Chem. Sot., Ckem. Commun. 19P1,3!&400. 11. For a review on functionahsed organolithium compounds, see: Najera, C.; Yus, M. De&s in Orgunic Ciwndy 1991,2, 155181. 12. (a) Yus, M.; Ran& D. J. .Z. Org. Client. 1992, 57,7SO-751. (b) Ramon, D. J.; Yus. M. Tem&edmz Lea. 1992, 33,2217-2220. (c) Guijarro, A.; Ram&, D. J.; Yus, M. Te&~~ 1993.49, 4c59-482. (d) Guijarro, A.; Yus, M. Tetrahehn Len. lPP3,34,201 I-2014. (e) Gknez. C.; Ram&t, D. J.; Yus, M. Tetrahedron 1993,49,4117-4126. (f) Gil, J. F.; Ram&, D, J.; Yus, M. Tetru~dro~ 1993,#9, 4923-4938. (g) Guijarro, A:; Yus, M. Tetrahedron Len. 1993,34,34&74390. (h) Ram&t, D. J.; Yus, M. Tetrdedron, in press. (1) Ram6n. D. J.; Y us, M. Tetr&?dron Len, in press. 13. (a) Ram&r, D. J.; Yus, M. Ten&e&on 1992,48.35&5-X%8. (b) Guijarro, D.; Man&&, B.; Yus, M. Tetruhedron 1992,48. 4!593-4600. (c) Gui’arro. D. ; Mancheiio, B. ; Yus, M. Tc@&d~~n Lea. 1992, 33,5597-5600. (d) Almena, J.; Foubelo, d .; Yus, h4. Tetrahedron L.&t. 1993, 34, 1649-1652. (e) Guijarro, D.: ManchefSo, B.; Yus, M. Tebvzhedron 1993.49. 1327-1334. (I) Guijarro. D.; Yus, M. Tetruhedron 1993,49,7761-7768. (g) Gil, J. F.; Ram&t. D. J.; Yus. M. Tetruhertron, in press. Vlaar, C. P.; Wumpp, G. W. Angew. Ch.em. In?. Ed. Engl. lPP3,32,5’74-576. For a review, see: Siegel, H. Top. Cwr. Chem. 1982,Z&5, B-78. :; 16: This type of intermediates, obtained by direct deprotonation of chlorohydrins. are stable at low temperatures (no epoxides are obtained after hydrolysis): Bariuenga, J.; F&&z, J.; Yus, M. J. Chem. tic.. Chem. Cormrnur. 19g2, 1153-1154. 17. &Reagents (Seebach, D. Angew. C&m. Iti. Ed. Engi. 1979, 28.239258) of this type have been prepared at low temperanne by (a) rn~~-~~~ ~me~lati~: Barhtenga, J.: Faftan&, E J.; Yus, M.; Asensio, G. ~e~u~~~~ Left. r978, 20152016. (b) Chlorine-lithium exchange: Batiuenga, 1.; FhSrez, F.; Yus. M. J. Chem. Sot., Perkin Trans. Z 1983, 3019-3026. (c) reductive opening of epoxidesz Bartmann, E. &gew. Chem. Zar. Ed. Z?agZ.1986,2.5,653-654. 18. Bates, R. B.; Kropo&, L. M.; Potter, D. E. J. Org. Chem. 1972,37, 560-562. Barluenga, J.; Yus, M.; Bernad, P. J. Gem. Sot., Chem. C~un. 1978.847. 1:: parham, W. E.; Schweizer, E. E Organic Reuc2ion.r; John Wiley and Sons, Inc.: New Yorlc, 1979: vol. 13, ch 2, pp. 74-75. 21. This work was finnacially supported by DGICYT (PB91-0751) from the Ministetio de Educacibn y Ciencia (MEC) of Spain. A. 0. thanks the MEC for a grant