1-Silyl-1-boryl-2-alkenes: Reagents for stereodivergent allylation leading to 4-oxy-(E)-1-alkenylboronates and 4-oxy-(Z)-1-alkenylsilanes

Article abstract of DOI:10.1002/1521-3773(20011119)40:22<4283::AID-ANIE4283>3.0.CO;2-3

Silylboryl reagents for organic synthesis: 1-silyl-1-boryl-2-alkenes (2) were prepared efficiently by gem-silylborylation of α-chloroallyllithium compounds from (dimethylphenylsilyl) (pinacolato)borane (1; see scheme, LDA = lithium diisopropylamide) and w

Full text of DOI:10.1002/1521-3773(20011119)40:22<4283::AID-ANIE4283>3.0.CO;2-3

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[11] a) J. M. Thomas, R. Raja, G. Sankar, R. G. Bell, Nature 1999, 398,
227 ± 230; b) A. Clearfield, Chem. Rev. 1988, 88, 125 ± 148; c) Y. F.
Shen, R. P. Zerger, R. N. DeGuzman, S. L. Suib, L. McCurdy, D. I.
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Tong, J. Y. Wang, N. G. Duan, V. V. Krishnam, S. L. Suib, Science 1997,
276, 926 ± 930.
ums and dual stereospecific allylation of aldehydes with
silicon or boron functionality of the gem-silylboryl reagents.
Recently, the novel gem-silylborylation reaction of 1-halo-
1-lithio-1-alkenes with (dimethylphenylsilyl)(pinacolato)bor-
ane (1) was disclosed[8] and is considered to proceed via borate
formation followed by 1,2-migration of a silyl group from an
ate-type boron to a carbenoid carbon. We envisaged that the
title gem-silylboryl reagents 2 might be prepared readily by
the gem-silylborylation with 1 of vinyl-substituted carbenoids
[Eq. (1)].[9, 10] Thus, we treated 1[11] with a-chloroallyllithiums
[12] C. L. OꢁYoung, R. A. Sawicki, S. L. Suib, Microporous Mater. 1997, 11,
1 ± 8.
[13] Although we did not experience any incidents during the alcohol
oxidation studies using our catalyst, adequate precautions need to be
taken against explosion hazards associated with toluene ± oxygen
vapors at the high reaction temperature. This is so because the lower
limit of flammability of toluene is a meager 1.2% by volume in air.
[14] R. A. Sheldon, M. Wallau, I. W. C. E. Arends, U. Schuchardt, Acc.
Chem. Res. 1998, 31, 485 ± 493.
1-Silyl-1-boryl-2-alkenes: Reagents for
Stereodivergent Allylation Leading to
4-Oxy-(E)-1-alkenylboronates and
4-Oxy-(Z)-1-alkenylsilanes**
generated in situ from allylic chlorides and lithium diisopro-
pylamide (LDA) in THF at 988C. The results are summar-
ized in Table 1. Allyl chloride was converted into 2a in 82%
yield (Entry 1). Substituted allylic chlorides were also gem-
silylborylated smoothly in good yields irrespective of the
substitution pattern (Entries 2 ± 7). No trace of g-silyl-a-
boration by 1,4-migration of a silyl group was observed.
Noteworthy is that the olefinic configuration was perfectly
retained in compounds 2 (Entries 3 ± 5): stereochemically
pure allylic chlorides gave single stereoisomers of 2.
Masaki Shimizu,* Hirotaka Kitagawa,
Takuya Kurahashi, and Tamejiro Hiyama*
Allylmetal reagents have been widely used in organic
synthesis.[1] In addition, allylic boranes[2] and silanes[3] are
highly versatile owing to their wide availability, high stability,
and low toxicity as well as excellent chemo-, regio-, and
stereoselectivities. In sharp contrast, little attention has been
paid to 1-silyl-1-boryl-2-alkenes, though such reagents can be
regarded as a hybrid of allylic boranes and silanes and are
attractive for the construction of stereochemically complex
molecules.[4] Yamamoto, Yatagai, and Maruyama prepared a-
trimethylsilyl-substituted crotyl-9-BBN (9-BBN ˆ 9-borabi-
cyclo[3.3.1]nonane) by deprotonation of crotyl-9-BBN fol-
lowed by silylation with chlorotrimethylsilane.[5] Similar
boronates were synthesized by Tsai and Matteson by the
homologation of alkenylboronates with [chloro(trimethyl-
silyl)methyl]lithium.[6] Both reagents were found to allylate
aldehydes[7] in a manner similar to allylic boranes. Although
this methodology is effective for acyclic stereocontrol, allyla-
tion with allylic silanes and stereospecificity in boron-
selective allylation remained to be explored. Herein we
describe the novel stereocontrolled synthesis of 1-silyl-1-
boryl-2-alkenes by gem-silylborylation of a-chloroallyllithi-
Table 1. Synthesis of 1-silyl-1-boryl-2-alkenes from allylic chlorides.[a]
Entry
Allylic chloride
Product
Yield [%][b]
1
82
‰cŠ
2
3
4
5
6
86[d]
75[e]
79[f]
75[e]
72
‰eŠ
‰fŠ
‰eŠ
[*] Dr. M. Shimizu, Prof. T. Hiyama, H. Kitagawa, T. Kurahashi
Department of Material Chemistry
Graduate School of Engineering
Kyoto University, Yoshida, Sakyo-ku, Kyoto, 606-8501 (Japan)
Fax : (‡81)75-753-5555
E-mail: thiyama@npc05.kuic.kyoto-u.ac.jp
7
73
[**] This work was supported by a Grant-in-Aid for COE Research on
Elements Science, No. 12CE2005 from the Ministry of Education,
Culture, Sports, Science, and Technology, Japan.
[a] allylic chloride (1.0 mol), 1 (1.1 mol), LDA (1.0 mol), THF, 988C,
10 min then warmed to room temperature. [b] Isolated yields are given.
[c] E/Z ˆ 85:15. [d] E/Z ˆ 83:17. [e] E/Z ˆ >99: < 1. [f] E/Z ˆ <1: > 99.
Supporting information for this article is available on the WWW under
http://www.angewandte.com or from the author.
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Table 2. Allylation of acetals or aldehydes with 2 as an allylic silane.[a]
We next scrutinized the allylation of 2 taking advantage of
allylic silane functionality. After many attempts,[12] we found
that compounds 2 allylated acetals in the presence of titanium
tetrachloride (Scheme 1).[13, 14] The results are summarized in
Entry
2
Electrophile Product
Yield [%][b] Isomer
ratio[c]
1
2a
78 (3)[d]
94:6[e]
2
3
2a
2a
77
95:5[e]
[f]
85
±
4
5
2a
2a
69
62
97:3[e]
Scheme 1. Allylation of acetals or aldehydes as allylic silanes. Bn ˆ benzyl,
OTf ˆ trifluoromethanesulfonate.
> 95: < 5[e]
Table 2. Aliphatic, aromatic, and a,b-unsaturated acetals
reacted with 2 to produce alkenylboronates 3a ± f in good
yields with high (E)-selectivity (Entries 1 ± 6). Moreover,
reagents 2 were shown to allylate an oxonium ion in situ
generated from an aldehyde, Me3SiOBn, and Me3SiOTf, to
give the corresponding (E)-benzyl ether 3g ± l stereoselec-
tively (Entries 7 ± 12).[15] High (E)-selectivity of 3 is observed
irrespective of the olefinic geometry of 2 (Entries 6, 9, 10, and
11).[16] Markedly, allylation by 1-silyl-(E)- and (Z)-2-hexenyl
boronates 2c and 2d proceeded stereospecifically with high
(E, erythro) and (E, threo) selectivities, respectively (En-
tries 10 and 11).[17] These results are the first demonstration of
silicon-selective allylation over boron in 2.
Allylation of aldehydes with allylic borane reagents 2a, 2c,
and 2d was also studied [Eq. (2)]. Some of results are
summarized in Table 3. Both aliphatic and aromatic alde-
hydes were allylated by 2a upon heating at 1008C in the
absence of any additive to yield the corresponding alkenylsi-
lanes 4a and 4b in moderate to good yields with high Z-
selectivity (Entries 1 and 2). Comparing with the results of
pinacol a-trimethylsilyl allylboronate,[6] the selectivity slightly
increased because of the bulkier dimethylphenylsilyl group.
Stereochemically pure (E)-2-hexenyl boronate 2c reacted
with benzaldehyde to give 4c in a (E, threo)/(Z, threo) ratio of
7:93 (Entry 3), whereas (E, erythro) isomer 4d was produced
by using 2d with 94% selectivity (Entry 4). The stereospecific
outcome is in accord with chairlike six-membered transition
states.[5, 6]
6
2b[g]
81
73:24:3[h]
7
8
2a
2a
85
> 95: < 5[e]
> 95: < 5[e]
88 (73)[i]
9
2b[g]
81
83
84:16[j]
10
2c
95:5[j]
11
12
2d
2g
94
70
9:91[j]
> 95: < 5[e]
[a] For acetals: 2 (1.0 mol), acetal (2.0 mol), TiCl4 (1.5 mol), CH2Cl2,
788C, 15 min. For aldehydes: aldehyde (1.0 mol), Me3SiOBn (1.3 mol),
Me3SiOTf (1.0 mol), CH2Cl2, 788C, 6 h, then 2 (1.0 mol), 788C, 12 h;
B ˆ B(OCMe2)2. [b] Isolated yields are given. [c] Determined by 1H NMR
of a crude product mixture. [d] (E)-3a: 78% yield; (Z)-3a: 3% yield.
[e] Ratios of E/Z. [f] The ratio was not determined. [g] E/Z Mixture of 2b
was used (E/Z ˆ 83:17). [h] Ratio of (E, erythro):(E, threo):others. [i] 88%:
Me3SiOTf (1.0 mol); 73%: Me3SiOTf (0.1 mol). [j] Ratio of (E, eryth-
ro):(E, threo).
Further synthetic elaboration of the allylated products with
the aid of the remaining inorganic functional group and
deprotection of benzyl group in 3 are illustrated in Scheme 2.
Suzuki ± Miyaura coupling[18] of 3d with iodobenzene gave
(E)-homoallylic ether 5, while methoxyethoxymethylation of
4c with methoxyethoxymethyl chloride (MEMCl) followed
by acetal-vinylsilane cyclization mediated by titanium tetra-
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either the silicon- or boron-functionality, and was demon-
strated that under appropriate conditions the corresponding
adducts are readily converted into substituted (E)- or (Z)-
homoallylic alcohols.
Experimental Section
Full experimental details and analytical data can be found in the
Supporting Information.
Table 3. Allylation of aldehydes with 2 as an allylic borane.[a]
2a, gem-silylborylation of allyl chloride: A solution of LDA (3.3 mmol) in
THF (8 mL) was added to a solution of allyl chloride (0.26 mL, 3.2 mmol)
and (dimethylphenylsilyl)(pinacolato)borane (1) (0.92 g, 3.5 mmol) in THF
(20 mL) at 988C. The reaction mixture was stirred for 10 min at 988C
and then allowed to gradually warm to room temperature. The solution was
stirred overnight followed by quenching with saturated aq. NH4Cl solution.
The aqueous layer was extracted with diethyl ether (20 mL). The organic
layer was dried over anhydrous MgSO4, and concentrated in vacuo to give
the crude product. Purification by column chromatography on silica gel
(hexane/ethyl acetate ˆ 9/1) afforded 2a as a colorless oil (0.79 g, 82%
yield); TLC: Rf ˆ 0.45 (hexane/ethyl acetate ˆ 9/1); 1H NMR (200 MHz,
CDCl3): d ˆ 0.34 (s, 3H), 0.35 (s, 3H), 1.13 (s, 6H), 1.16 (s, 6H), 1.79 (d, J ˆ
10.5 Hz, 1H), 4.74 (ddd, J ˆ 16.8, 2.2, 0.6 Hz, 1H), 4.78 (dd, J ˆ 10.5, 2.2 Hz,
1H), 5.85 (ddd, J ˆ 16.8, 10.5, 10.5 Hz, 1H), 7.28 ± 7.38 (m, 3H), 7.48 ± 7.60
(m, 2H); 13C NMR (50 MHz, CDCl3): d ˆ 3.2, 3.2, 24.7, 24.8, 82.8, 112.2,
127.4, 128.8, 133.9, 135.3, 138.0; IR (neat): nÄ ˆ 2985, 1623, 1374, 1339, 1318,
Entry
2
Aldehyde Product
Yield [%][b] Isomer ratio[c]
1
2a
74 (17)
89 (0)
15:85[d]
9:91[d]
2
3
2a
2c
87 (10)
46 (20)
7: 93[e]
‡
‡
‡
1145, 839 cm 1; MS (EI, 70 eV): m/z 303 (M ‡1, 1), 302 (M , 5), 301 (M
4[f]
2d
94:6[g]
‡
‡
1, 1), 284 (M
Me, 6), 245 (28), 235 (M
Ph, 13), 202 (32), 187 (32), 160
‡
(49), 135 (PhMe2Si , 100); elemental analysis (%) calcd for C17H27BO2Si: C
67.55, H 9.00; found: C 67.29, H 8.92.
[a] 2 (1.0 mol), aldehyde (1.1 mol), THF, 1008C, 24 h. Si ˆ SiMe2Ph.
[b] Isolated yields are given. The values in parentheses are recovery of 2.
[c] Determined by 1H NMR. [d] Ratio of E/Z. [e] Ratio of (E, threo):(Z,
threo). [f] Benzaldehyde (3 molar equivalents) was treated at 658C for 45 h.
[g] Ratio of (E, erythro):(Z, threo).
Allylation of acetaldehyde dimethylacetal with 2a: A solution of TiCl4 in
CH2Cl2 (1.0m, 0.82 mL, 0.82 mmol) was added to a solution of 2a (0.17 g,
0.55 mmol) and acetaldehyde dimethylacetal (116 mL, 1.10 mmol) in
CH2Cl2 (6 mL) at 788C. The solution was stirred for 15 min at 788C
before quenching with water (0.50 mL) at
788C. The mixture was
warmed to room temperature, dried over anhydrous MgSO4, and filtered.
The filtrate was concentrated to give a crude product consisting of E/Z ˆ
94:6 as revealed by 1H NMR spectra. Purification by silica gel column
chromatography (hexane/ethyl acetate ˆ 2/1) afforded (E)-3a (97 mg, 78%
yield) and (Z)-3a (4.1 mg, 3% yield). (E)-3a: colorless oil; thin layer
chromatography (TLC): Rf ˆ 0.53 (hexane/ethyl acetate ˆ 2/1); 1H NMR
(200 MHz, CDCl3): d ˆ 1.15 (d, J ˆ 6.0 Hz, 3H), 1.27 (s, 3H), 2.27 (ddd, J ˆ
14.4, 6.6, 1.5 Hz, 1H), 2.44 (ddd, J ˆ 14.4, 6.6, 1.5 Hz, 1H), 3.32 (s, 3H), 3.42
(m, J ˆ 6.0 Hz, 1H), 5.50 (dt, J ˆ 18.1, 1.5 Hz, 1H), 6.60 (dt, J ˆ 18.1, 6.6 Hz,
1H); 13C NMR (50 MHz, CDCl3): d ˆ 19.1, 24.8, 42.6, 56.0, 75.9, 83.1, 150.3.
IR (neat): nÄ ˆ 2980, 2935, 1640, 1362, 1321, 1146, 998, 972, 852 cm 1. MS
‡
‡
(EI, 70 eV): m/z 225 (M
1, 0.6), 211 (M
Me, 17), 111 (9), 101 (8.0), 95
(8), 59 (100); elemental analysis (%) calcd for C12H23BO3: C 63.74, H 10.25;
found: C 63.62, H 10.41.
Allylation of benzaldehyde with 2a: A solution of 2a (0.13 g, 0.42 mmol)
and benzaldehyde (47 mL, 0.46 mmol) in THF (4 mL) was stirred at 1008C
(oil bath) for 24 h. The reaction mixture was cooled to room temperature,
and then ethanolamine (42 mL) was added to the mixture at room
temperature. The resulting milky suspension was stirred for 30 min.
Filtration of the insoluble material followed by concentration of the
filtrate gave a crude product. Purification by silica gel column chromatog-
raphy (hexane/ethyl acetate ˆ 4/1) gave 4b as a colorless oil (0.11 g, 89%
yield, E/Z ˆ 9:91); TLC: Rf ˆ 0.31 (hexane/ethyl acetate ˆ 4/1); 1H NMR
(200 MHz, CDCl3): d ˆ 0.38 (s, 6H), 1.77 (brs, 1H), 2.35 ± 2.65 (m, 2H), 4.64
(dd, J ˆ 7.4, 5.6 Hz, 1H), 5.85 (dt, J ˆ 13.9, 1.3 Hz, 1H), 6.46 (dt, J ˆ 13.9,
7.4 Hz, 1H), 7.16 ± 7.42 (m, 8H), 7.48 ± 7.58 (m, 2H); 13C NMR (50 MHz,
CDCl3): d ˆ 1.0, 1.0, 43.0, 73.6, 125.7, 127.4, 127.8, 128.3, 128.9, 130.6, 133.7,
139.3, 143.8, 145.6. IR (neat): nÄ3400 (br), 3070, 3035, 2965, 2900, 1608, 1428,
Scheme 2. Synthetic applications of allylated products 3d, 3 h, and 4c.
a) PhI (1.1 mol), [Pd(PPh3)4] (4.9 mol%), aq. KOH (3.0 mol), dioxane,
1008C, 86% yield; b) NaH (5.1 mol), MEMCl (6.1 mol), THF, RT, 55%
yield; c) TiCl4 (3.0 mol), CH2Cl2, 788C, 82% yield; d) Me3SiI (1.3 mol),
CH2Cl2, RT, 73% yield.
chloride gave trans-6-phenyl-5-propyl-5,6-dihydro-2H-pyran
(6).[19] Debenzylation of 3 h was carried out in good yield by
treatment with Me3SiI with retention of the (E)-alkenylboryl
moiety.[20]
In summary, we have demonstrated that gem-silylboryla-
tion of stereochemically defined a-chloroallyllithiums with
silylborane 1 constitutes a new method for the stereocon-
trolled synthesis of 1-silyl-1-boryl-2-alkenes 2. Furthermore,
stereospecific allylation of aldehydes with 2 was achieved with
‡
‡
1250, 1114, 1053, 822 cm 1; MS (EI, 70 eV): m/z 283 (M ‡ 1, 0.3), 282 (M ,
‡
‡
‡
0.5), 281 (M
1, 2), 264 (M
H2O, 13), 249 (M
H2O Me, 16), 241
‡
‡
(34), 173 (52), 145 (36), 135 (PhMe2Si , 91), 121 (47), 107 (PhCHOH , 100);
elemental analysis (%) calcd for C18H22OSi: C 76.54, H 7.85; found: C
76.82, H 7.88.
Received: March 20, 2001
Revised: September 3, 2001 [Z16815]
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COMMUNICATIONS
[1] Reviews on allylmetal reagents: a) Y. Yamamoto, N. Asao, Chem. Rev.
1993, 93, 2207 ± 2293; b) W. R. Roush in Comprehensive Organic
Synthesis, Vol. 2 (Eds.: B. M. Trost, I. Fleming, C. H. Heathcock),
Pergamon, Oxford, 1991, pp. 1 ± 53; c) R. W. Hoffmann, Angew.
Chem. 1982, 94, 569; Angew. Chem. Int. Ed. Engl. 1982, 21, 555 ± 566.
[2] a) E. Negishi, M. J. Idacavage, Org. React. 1985, 33, 1 ± 246; b) A.
Pelter, K. Smith, H. C. Brown, Borane Reagents, Academic Press, New
York, 1988, pp. 310 ± 323; c) D. S. Matteson, Stereodirected Synthesis
with Organoboranes, Springer, Berlin, 1995, pp. 260 ± 310.
[3] a) H. Sakurai, Pure Appl. Chem. 1982, 54, 1 ± 22; b) A. Hosomi, Acc.
Chem. Soc. 1988, 21, 200 ± 206; c) I. Fleming in Comprehensive
Organic Synthesis, Vol. 2 (Eds.: B. M. Trost, I. Fleming, C. H. Heath-
cock), Pergamon, Oxford, 1991, pp. 563 ± 593; d) I. Fleming, Org.
React. 1994, 33, 1 ± 246; e) C. E. Masse, J. S. Panek, Chem. Rev. 1995,
95, 1293 ± 1316.
[4] Reviews of gem-dimetallic reagents: a) I. Marek, J.-F. Normant,
Chem. Rev. 1996, 96, 3241 ± 3267; b) I. Marek, Chem. Rev. 2000, 100,
2887 ± 2900; other kinds of allyldimetallic compounds: (Si, Al) c) E.-i.
Negishi, K. Akiyoshi, J. Am. Chem. Soc. 1988, 110, 646 ± 647; (Si, Si)
d) D. M. Hodgson, S. F. Barker, L. H. Mace, J. R. Moran, Chem.
Commun. 2001, 153 ± 154; e) B. Princet, H. Gardes-Gariglio, J. Pornet,
J. Organomet. Chem. 2000, 604, 186 ± 190; f) M. Lautens, P. H. M.
Delanghe, Angew. Chem. 1994, 106, 2557; Angew. Chem. Int. Ed. Engl.
1994, 33, 2448 ± 2450; g) M. Lautens, R. N. Ben, P. H. M. Delanghe,
Tetrahedron 1996, 52, 7221 ± 7234; (Si, Zr) h) A. N. Kasatkin, R. J.
Whitby, Tetrahedron Lett. 1999, 40, 9353 ± 9357; (Si, Sn) i) M. Lautens,
A. H. Huboux, B. Chin, J. Downer, Tetrahedron Lett. 1990, 31, 5829 ±
5832; (Sn, Sn) j) refs. [4f] and [4g]; k) H. J. Reich, J. W. Ringer, J. Org.
Chem. 1988, 53, 455 ± 457; l) see also ref. [4i]; m) D. Madec, J.-P.
Ferezou, Tetrahedron Lett. 1997, 38, 6657 ± 6660; n) D. Madec, J.-P.
Ferezou, Tetrahedron Lett. 1997, 38, 6661 ± 6664.
[14] Reaction of 1-silyl-1-stannyl-2-alkenes with acetals in the presence of
BF3 ´ OEt2 was reported in which
carbon ± tin bond cleaved
a
selectively over a carbon ± silicon bond giving rise to (E)-alkenylsi-
lanes. See, ref. [4g].
[15] For in situ generation of oxonium ions: a) A. Mekhalfia, I. E. Marko,
Tetrahedron Lett. 1991, 32, 4779; b) J. S. Panek, M. Yang, F. Xu, J. Org.
Chem. 1992, 57, 5790. See also, R. Noyori, S. Murata, M. Suzuki,
Tetrahedron 1981, 37, 3899.
[16] (E)-Olefinic selectivity can be explained by anti-SE2' transition states
of allylsilanes. See, a) T. Hayashi, M. Konishi, H. Ito, M. Kumada, J.
Am. Chem. Soc. 1982, 104, 4962 ± 4963; b) T. Hayashi, M. Konishi, M.
Kumada, J. Am. Chem. Soc. 1982, 104, 4963 ± 4965.
[17] Relative stereochemistry between benzyloxy and propyl groups of 3k
being threo was confirmed by protodeborylation of 3k to convert it
into 3-[benzyloxy(phenyl)methyl]-1-hexene that was consistent with
the product obtained by benzylation and protodesilylation of 4c.
Erythro selectivity using the (E)-allylic silane may be explained by
acyclic antiperiplanar transition states (see refs. [13d] and [15b]).
However, such a model cannot rationalize threo selectivity from the
(Z)-allylic silane. Although the reason for threo selectivity is not clear
at present, acyclic synclinal transition states (see, ref. [3e]) might be
involved considering the steric effect of a boryl group [Eq. (3)].
[18] N. Miyaura, A. Suzuki, Chem. Rev. 1995, 95, 2457 ± 2483.
[19] L. E. Overman, A. Castaneda, T. A. Blumenkopf, J. Am. Chem. Soc.
1986, 108, 1303 ± 1304.
[20] T. W. Greene, P. G. M. Wuts, Protective Groups in Organic Synthesis,
3rd ed., Wiley, New York, 1999.
[5] a-Trimethylsilyl crotyl-9-BBN was obtained as a mixture of E/Z
isomers as a result of the allylic rearrangement. a) H. Yatagai, Y.
Yamamoto, K. Maruyama, J. Am. Chem. Soc. 1980, 102, 4548 ± 4550;
b) Y. Yamamoto, H. Yatagai, K. Maruyama, J. Am. Chem. Soc. 1981,
103, 3229 ± 3231; see also, c) Y. Yamamoto, Y. Saito, K. Maruyama, J.
Organomet. Chem. 1985, 292, 311 ± 318.
[6] A ꢀ2:1 mixture of pinacol (Z)- and (E)-a-trimethylsilyl crotylboro-
nate was obtained. a) D. J. S. Tsai, D. S. Matteson, Organometallics
1983, 2, 236 ± 241; see also, b) D. S. Matteson, D. Majumdar, Organo-
metallics 1983, 2, 230 ± 236.
[7] Allylation of activated carbonyl pyruvates by a-trimethylsilyl crotyl-9-
BBN was also reported. a) Y. Yamamoto, T. Komatsu, K. Maruyama,
J. Chem. Soc. Chem. Commun. 1983, 191 ± 192; b) Y. Yamamoto, K.
Maruyama, T. Komatsu, W. Ito, J. Org. Chem. 1986, 51, 886 ± 891.
[8] T. Hata, H. Kitagawa, H. Masai, T. Kurahashi, M. Shimizu, T. Hiyama,
Angew. Chem. 2001, 113, 812 ± 814; Angew. Chem. Int. Ed. 2001, 40,
790 ± 792.
Organoclay Derivatives in the Synthesis of
Macrocycles
Vasilios Georgakilas, Dimitrios Gournis, and
Dimitrios Petridis*
[9] Reviews of heteroatom-stabilized allylanions: a) Y. Yamamoto in
Comprehensive Organic Synthesis, Vol. 2 (Eds.: B. M. Trost, I. Flem-
ing, C. H. Heathcock), Pergamon, Oxford, 1991, pp. 55 ± 79; b) A. R.
Katritzky, M. Piffl, H. Lang, E. Anders, Chem. Rev. 1999, 99, 665 ± 722;
generation and reactions of a-chloroallyllithiums: c) T. L. Macdonald,
B. A. Narayanan, D. E. OꢁDell, J. Org. Chem. 1981, 46, 1504 ± 1506;
d) M. Julia, J.-N. Verpeaux, T. Zahneisen, Bull. Soc. Chim. Fr. 1994,
131, 539 ± 554.
[10] Synthesis of allylic boranes by reactions of a-chloroallyllithiums and
organoboron compounds: a) H. C. Brown, M. V. Rangaishenvi, Tet-
rahedron Lett. 1990, 31, 7113 ± 7114; b) H. C. Brown, M. V. Rangaish-
envi, Tetrahedron Lett. 1990, 31, 7115 ± 7118; c) H. C. Brown, M. V.
Rangaishenvi, S. Jayaraman, Organometallics 1992, 11, 1948 ± 1954;
d) H. C. Brown, S. Jayaraman, J. Org. Chem. 1993, 58, 6791 ± 6794.
[11] M. Suginome, T. Matsuda, Y. Ito, Organometallics 2000, 19, 4647± 4649.
[12] For example, TiCl4-promoted allylation of benzaldehyde with 2a
resulted in protodesilylation of 2a producing 1-propenylboronate as a
major isomer in low yield, while the same reaction mediated by Bu4NF
afforded a complex mixture.
The synthesis of macrocyclic systems is profoundly hin-
dered by reactions of participating components that lead to
the formation of mainly oligomeric or polymeric compounds.
To overcome this deficiency, template-assisted methods based
on metal coordination, electron-donor interactions, hydrogen
bonding, and electrostatic interactions have been successfully
developed.[1] In these reactions the templating agent plays the
essential role of assembling and organizing the participating
molecules in a way that makes possible a desirable reaction
pathway that would not occur in its absence.[2]
Another potential approach to effectively assemble and
organize compounds into well-defined supramolecular arrays
[*] Dr. D. Petridis, Dr. V. Georgakilas, Dr. D. Gournis
Institute of Materials Science
NCSR ªDemokritosº Ag. Paraskevi Attikis, Athens (Greece)
Fax : (‡30)1-6519430
[13] a) Review on coupling reactions of acetals: T. Mukaiyama, M.
Murakami, Synthesis 1987, 1043 ± 1054; b) A. Hosomi, M. Endo, H.
Sakurai, Chem. Lett. 1976, 941 ± 942; c) A. Hosomi, M. Ando, H.
Sakurai, Chem. Lett. 1986, 365 ± 368; d) J. S. Panek, M. Yang, J. Am.
Chem. Soc. 1991, 113, 6594 ± 6600.
E-mail: dpetrid@ims.demokritos.gr
Supporting information for this article is available on the WWW under
http://www.angewandte.com or from the author.
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