The use of the Mitsunobu reaction in preparation of chiral synthons for macrocyclic frameworks

Article abstract of DOI:10.1016/S0957-4166(98)00154-2

The Mitsunobu reaction was used for the synthesis of chiral diesters 2 and 6 and chiral diamine 4. Five new chiral macrocyclic bisamides were synthesized, starting from these precursors.

Full text of DOI:10.1016/S0957-4166(98)00154-2

TETRAHEDRON:
ASYMMETRY
Pergamon
Tetrahedron: Asymmetry 9 (1998) 1771–1778
The use of the Mitsunobu reaction in preparation of chiral
synthons for macrocyclic frameworks
Daniel T. Gryko,a Piotr Pia˛tek,b Piotr Sałan´ski a and Janusz Jurczak a,b,∗
aInstitute of Organic Chemistry, Polish Academy of Sciences, 01-224 Warsaw, Poland
bDepartment of Chemistry, University of Warsaw, 02-093 Warsaw, Poland
Received 25 March 1998; accepted 20 April 1998
Abstract
The Mitsunobu reaction was used for the synthesis of chiral diesters 2 and 6 and chiral diamine 4. Five new
chiral macrocyclic bisamides were synthesized, starting from these precursors. © 1998 Elsevier Science Ltd. All
rights reserved.
1. Introduction
The increasing interest in the molecular recognition and complexing properties of naturally occurring
macrocycles has attracted much attention in the design and synthesis of new cyclic polyaza- and
polyoxamacrocycles.1 The cavity size and rigidity of a macrocycle are important in governing the
host–guest interactions and in the complexation selectivity of metal ions.2 Among others, macrocyclic
amides are used as host molecules. They act as hydrogen-bond donors and hydrogen-bond acceptors
and can complex neutral molecules of biological interest.3 The most popular method for preparation
of macrocyclic amides consists in reacting a diacid dichloride with a diamine under high-dilution
conditions.4 At the beginning of the nineties we found5 that α,ω-diamino aliphatic ethers react under
ambient conditions with dimethyl α,ω-dicarboxylates, to afford the macrocyclic bisamides which can
be readily transformed into diamines using, for example, BH3·Me2S. The optimum reaction conditions
proposed by us are as follows: methanol as a solvent, concentration ∼0.1 M, room temperature, seven
days. Similar conditions have been used recently for preparing several various types of macrocyclic
amides.6,7
The above-mentioned reaction requires α,ω-diamines and dimethyl esters of α,ω-dicarboxylic acids
possessing ether oxygen atoms. More complex compounds of this type are not always readily available.
The alkylation of alcohols or phenols with functionalized alkyl halides is frequently used as the most
∗
Corresponding author. E-mail: jurczak@ichf.edu.pl
0957-4166/98/$19.00 © 1998 Elsevier Science Ltd. All rights reserved.
PII: S0957-4166(98)00154-2

1772
D. T. Gryko et al. / Tetrahedron: Asymmetry 9 (1998) 1771–1778
versatile procedure for the synthesis of these compounds.7,8 However, in the case of more elaborate
compounds this method failed sometimes.9 The use of the triphenylphosphine/diethyl azadicarboxylate
(TPP/DEAD) protocol, known as the Mitsunobu reaction,10 for coupling phenols and alcohols to form
ethers, has been recently widely used in the synthesis of macrocyclic lactones,9 dendrons,11 2,20-
BINOL analogs,12 etc. Conversion of alcohols into amines is accomplished by coupling an alcohol with
phthalimide using TPP/DEAD, followed by hydrazinolysis of the phthalimide product to the desired
amine.13 Since the Mitsunobu reaction is compatibile with a large variety of different substituents it
might be an attractive alternative to other common procedures.14
2. Results and discussion
Treatment of an alcohol with TPP/DEAD results in the formation of a reactive triphenylphosphonium
intermediate which is displaced by the conjugate base of the phenol in an SN2 type reaction. The
advantage of this procedure is that transformation of the alcohol into a leaving group and its nucleophilic
substitution are performed in a single reaction step. Moreover, it is usually a mild and stereochemically
clean SN2 reaction which leads to products in generally high yields. Keeping in mind these advantages,
we resolved to utilize the Mitsunobu reaction in the preparation of a few chiral, interesting substrates
suitable for the preparation of elaborated chiral benzophanes. In this work we would like to show that
it is possible to synthesize interesting ethers as well as amines, from cheap chiral sources, using the
Mitsunobu reaction which seems to be the most efficient way to form the ether linkage. Next, we
decided to describe, following the procedure adapted previously, a few examples of the synthesis of
chiral macrocyclic bisamides from diesters 2 and 6 and diamine 4. We have choosen as a major substrate
(S,S)-2,3-O-benzylidenethreitol 1, readily available from L-tartaric acid.15,16 Thus, the reaction of methyl
salicylate with diol 1, carried out under Mitsunobu conditions, provided chiral ester 2 in 25% yield
(Scheme 1). This low yield seems to be the result of the formation of 3,4-O-benzylidenetetrahydrofuran
as a by-product. It is well known that such intramolecular coupling of diols caused by the TPP/DEAD
system leads to 3- to 7-membered cyclic ethers.17
The same diol 1 was converted into diamine 4. The Mitsunobu reaction, followed by exposure of the
resulting intermediate 3 to hydrazine hydrate, resulted in formation of the chiral diamine 4 in an overall
yield of 58% (Scheme 1).
Additionally we resolved to use our approach to synthesize another chiral α,ω-diester containing an
aromatic nucleus. Thus, the reaction of 1,3-dihydroxybenzene with ethyl L-lactate 5 performed under
Mitsunobu conditions afforded, in a convergent route, pure diastereoisomeric ester 6 in a yield of 53%,
as a result of inversion of configuration of the starting ester 5 (Scheme 1). All attempts to carry out the
analogous synthesis from catechol failed.
Next we used these three chiral compounds (2, 4 and 6) as substrates in the macrocyclization reaction.
The reaction of diester 2 with amine 7 failed under standard conditions. After eight weeks we recovered
100% of ester 2. In the light of these results, we resolved to modify the reaction conditions using the
high-pressure technique.5b,18 Under high-pressure conditions the synthesis of bisamide 8 was performed
in a yield of 39% (Scheme 2).
In the synthesis of macrocycle 9, we applied conditions that were developed by us for reactions of
various di-tert-butyl esters with amine 7 affording macrocyclic bisamides.19 Treatment of ester 6 with
amine 7 in the presence of DBU as a transesterification catalyst provided, via the appropriate dimethyl
ester, macrocyclic bisamide 9 in a yield of 20% (Scheme 2).7
Considering the rigid structure of diamine 4, we expected that the results of the macrocyclization

D. T. Gryko et al. / Tetrahedron: Asymmetry 9 (1998) 1771–1778
1773
Scheme 1. (a) Lit.5; (b) lit.6; (c) methyl salicylate, DEAD, PPh3, THF; (d) phthalimide, DEAD, PPh3, THF; (e) H2N–NH2·H2O,
PriOH, reflux; (f) DEAD, PPh3, THF
Scheme 2. (a) MeOH, RT, 8 kbar; (b) MeOH, DBU, RT
would depend on the length of the diester and its rigidity. Reactions of the diamine with some selected
diesters afforded the expected macrocyclic bisamides in moderate to good yields.

1774
D. T. Gryko et al. / Tetrahedron: Asymmetry 9 (1998) 1771–1778
Condensation of diamine 4 with ester 10 yielded bisamide 13 in a yield of 32% (Scheme 3). The
reaction of diamine 4 with ester 11, a compound readily available from catechol,7 provided macrocyclic
bisamide 14 in 20% yield (Scheme 3). Finally, we resolved to use chiral diamine 4 and chiral ester 12 for
preparation of macrocyclic bisamide 15 possessing stereogenic centers derived from both substrates. We
carried out experiments with chiral tert-butyl ester 12, obtained by us previously,19 under two different
conditions, i.e. under high pressure and in the presence of DBU19 (Scheme 3). Under high-pressure
conditions, the yield is five times lower than under DBU conditions (10% and 49%, respectively). This
suggests that substrates 4 and 12 are strongly adapted spaciously and that an influence of high pressure
on the reaction of diamines with diesters is highly sophisticated.
Scheme 3. (a) MeOH, RT; (b) MeOH, DBU, RT; (c) MeOH, RT, 12 kbar
We proved that the Mitsunobu reaction is very useful in the preparation of chiral α,ω-diesters and
α,ω-diamines. Additionally, we showed that these compounds can be transformed into various chiral
benzophanes with good yields.
3. Experimental
3.1. General methods
Melting points were taken on a Köfler type (Boetius) hot stage apparatus and are not corrected. Optical
1
rotations were recorded using a JASCO DIP-360 polarimeter with a thermally jacketed 10 cm cell. H
NMR spectra were recorded with a Varian Gemini (200 MHz) and/or a Bruker AM500 (500 MHz)
spectrometer in CDCl3 or DMSO-d6 using TMS as an internal standard. 13C NMR spectra were also
recorded using a Varian Gemini (50 MHz) and/or a Bruker AM500 (125 MHz) spectrometer. All chemical
shifts are quoted in parts per million relative to tetramethylsilane (δ, 0.00 ppm), and coupling constants

D. T. Gryko et al. / Tetrahedron: Asymmetry 9 (1998) 1771–1778
1775
(J) are measured in hertz. High-resolution mass spectrometry (HRMS) experiments were performed on
an AMD-604 Intectra instrument using the electron impact (EI) technique. Column chromatography was
carried out on silica gel (Kieselgel-60, 200–400 mesh). α,ω-Diamine 7 was purchased from Fluka. Diol
115,16 and esters 10,20 117 and 1219 were prepared according to the literature procedures.
3.2. Methyl
2-[((4S,5S)-5-{[2-(methyloxycarbonyl)phenoxy]methyl}-2-phenyl-1,3-dioxolan-4-ylo)
methoxy] benzoate 2
Diethyl azodicarboxylate (4.5 mL, 29 mmol) was added at 0°C to a solution of diol 1 (3.0 g, 14.3
mmol), methyl salicylate (3.75 mL, 29 mmol) and triphenylphosphine (7.87 g, 30 mmol) in 50 mL
anhydrous THF. The mixture was stirred for 48 h at room temperature. Then the solvent was evaporated
and the residue was chromatographed on a silica gel column using an n-hexane/ethyl acetate system as
an eluent to afford diester 2 (1.71 g, 25%) as a thick, colourless oil: [α]D23=+53.3 (c 1.0, CHCl3); δH
(200 MHz, CDCl3): 7.81 (m, 2H); 7.6–7.3 (m, 7H); 7.1–6.9 (m, 4H); 6.22 (s, 1H); 4.9–4.6 (m, 2H);
4.5–4.3 (m, 4H); 3.86 (s, 3H); 3.78 (s, 3H); δC (50 MHz, CDCl3): 166.5; 166.4; 158.0; 137.2; 133.5;
133.4; 131.8; 131.6; 129.5; 128.3; 126.8; 120.8; 120.7; 120.4; 120.3; 113.3; 113.1; 104.6; 77.6; 76.6;
69.0; 68.8; 51.9; 51.8; HRMS calcd for C27H26O8 (M)+ 478.1628, found 478.1625.
3.3. 2-({(4S,5S)-5-[(1,3-Dioxo-2,3-dihydro-1H-2-isoindolyl)methyl]-2-phenyl-1,3-dioxolan-4-yl}
methyl-1,3-isoindolinodione 3
Diethyl azodicarboxylate (5.3 mL, 34 mmol) was added at 0°C to a solution of diol 1 (3.0 g, 14.3
mmol), phthalimide (5.0 g, 34 mmol) and triphenylphosphine (9.0 g, 34 mmol) in 100 mL anhydrous
THF. The mixture was stirred for 48 h at room temperature, the precipitated product was isolated
by filtration and washed with cold THF. After removing the solvent from the fitrate by evaporation,
additional product was isolated which had to be recrystallized from methanol. The combined crystals
were chromatographed on a silica gel column using an n-hexane/ethyl acetate system as an eluent, to
afford compound 3 (3.7 g, 61%) as colourless crystals: [α]D23=−46.6 (c 1.0, DMSO); mp 200–201°C;
δH (500 MHz, CDCl3): 7.79 (m, 4H); 7.68 (m, 4H); 7.48 (m, 2H); 7.4–7.2 (m, 3H); 6.08 (s, 1H); 4.53 (m,
1H); 4.45 (m, 1H); 4.2–3.8 (m, 4H); δC (125 MHz, CDCl3): 168.1; 168.0; 136.5; 134.0; 133.9; 131.9;
131.8; 129.4; 128.3; 126.7; 123.4; 103.5; 77.1; 77.0; 40.6; 38.9; HRMS calcd for C27H20N2O6 (M)+
468.1321, found 468.1324.
3.4. [(4S,5S)-5-(Aminomethyl)-2-phenyl-1,3-dioxolan-4-yl]-methanamine 4
Hydrazine hydrate (3.94 mL, 126 mmol) was added to a stirred solution of compound 3 (3.7 g, 7.9
mmol), and the solution was heated to reflux for eight hours. It was then cooled to room temperature, and
the solvent was removed under reduced pressure. The residue was dissolved in NaOH (30 mL, 20%), and
the resulting two layers were then extracted with CH2Cl2 (3×50 mL). The combined organic solution
was then dried (Na2SO4). The filtrate was evaporated to leave the diamine as a pale yellow oil. Crude
product was then distilled under reduced pressure in a Kugelrohr apparatus (120°C, 0.2 mmHg) to afford
the diamine 4 (1.56 g, 95%) as a colourless oil, which has to be stored under argon because CO2 from the
air is strongly absorbed: δH (200 MHz, CDCl3): 7.6–7.3 (m, 5H); 5.94 (s, 1H); 4.0–3.9 (m, 2H); 3.1–2.8
(m, 4H); 1.6–1.2 (bs, 4H); δC (50 MHz, CDCl3): 137.5; 129.3; 128.2; 126.5; 103.0; 81.6; 80.7; 44.1;
43.9; HRMS calcd for C11H17N2O2 (M+H)+ 209.1290, found 209.1292.

1776
D. T. Gryko et al. / Tetrahedron: Asymmetry 9 (1998) 1771–1778
3.5. Ethyl (2S)-2-(3-{[(1S)-1-(ethyloxycarbonyl)ethyl]oxy}phenoxy) propanoate 6
Diethyl azodicarboxylate (3.1 mL, 19.7 mmol) was added at 0°C to a solution of 1,3-dihydroxybenzene
(1.0 g, 9.1 mmol), ethyl L-lactate (2.1 mL, 18.4 mmol) and triphenylphosphine (5.0 g, 19.1 mmol) in
20 mL anhydrous THF. The mixture was stirred for 48 h at room temperature. Then the solvent was
evaporated and the residue was chromatographed on a silica gel column using an n-hexane/ethyl acetate
system as an eluent, to afford diester 6 (1.48 g, 53%, >97% d.e. from 1H NMR) as a thick, colourless oil:
[α]D23=+40.9 (c 1.5, CHCl3); δH (200 MHz, CDCl3): 7.2–7.0 (m, 1H); 6.6–6.3 (m, 3H); 4.70 (q, J=6.8,
2H); 4.22 (q, J=7.1, 4H); 1.59 (d, J=6.8, 6H); 1.25 (t, J=7.1, 6H); δC (50 MHz, CDCl3): 172.0; 158.7;
129.9; 108.0; 103.0; 72.6; 61.2; 18.4; 14.0; HRMS calcd for C16H22O6 (M)+ 310.1416, found 310.1424.
3.6. General procedures for the synthesis of macrocyclic bisamides
Method A (standard conditions): An equimolar 0.1 M methanolic solution (1.5 mmol) of α,ω-diamine
and dimethyl α,ω-dicarboxylate was left at ambient temperature over a period of 7 days. Then the solvent
was evaporated and the residue was chromatographed on a silica gel column using 0–3% mixtures of
methanol in chloroform.
Method B (under high pressure): A Teflon ampoule was filled with an equimolar solution of the
dimethyl α,ω-dicarboxylate (0.5 mmol) and the appropriate α,ω-diamine (0.5 mmol) in 5 mL of
methanol and was placed in a high-pressure vessel filled with ligroine as a transmission medium and
compressed (12 kbar) at room temperature for 48 h. After decompression, the reaction mixture was
transferred quantitatively to a round-bottomed flask and the solvent was evaporated. The residue was
chromatographed on a silica gel column using 0–3% mixtures of methanol in chloroform.
Method C (with DBU): An equimolar 0.1 M methanolic solution (1.5 mmol) of α,ω-diamine and
dimethyl α,ω-dicarboxylate containing DBU (20 mol%) was left at ambient temperature over a period
of 21 days. Then the solvent was evaporated and the residue was chromatographed on a silica gel column
using 0–3% mixtures of methanol in chloroform.
3.7. (22aS,25aS)-24-Phenyl-5,6,7,8,10,11,13,14,15,16,22,22a,25,26-tetrahydrodibenzo-[i,q][1,3] diox-
olo[4,5-m][1,4,11,16,7,20]tetraoxadiazacyclodocosine-5,16-dione 8
Method B, yield 39%; [α]D23=+3.2 (c 1.0, CHCl3); δH (500 MHz, CDCl3): 8.28 (m, 2H); 8.19 (m,
2H); 7.5–7.4 (m, 4H); 7.37 (m, 3H); 7.2–6.9 (m, 4H); 6.16 (s, 1H); 4.73 (m, 2H); 4.40 (m, 4H); 3.7–3.3
(m, 12H); δC (125 MHz, CDCl3): 165.0; 164.9; 156.3; 156.2; 136.7; 132.7; 132.3; 132.2; 129.7; 128.4;
126.3; 122.7; 122.4; 122.3; 122.2; 113.2; 113.0; 104.3; 76.9; 76.7; 70.1; 69.9; 69.4; 69.2; 69.1; 69.0;
39.7; 39.3; HRMS calcd for C31H34N2O8 (M)+ 562.2315, found 562.2310.
3.8. (3S,16S)-3,16-Dimethyl-2,8,11,17-tetraoxa-5,14-diazabicyclo[16.3.1]docosa-1(21),18(22),19-
triene-4,15-dione 9
Method C, yield 20%; δH (500 MHz, CDCl3): 7.15 (m, 1H); 6.7–6.5 (m, 2H); 6.6–6.4 (m, 3H); 4.58
(q, J=6.8, 2H); 3.9–3.0 (m, 12H); 1.60 (d, J=6.8, 6H); δC (125 MHz, CDCl3): 172.2; 158.5; 130.1; 107.9;
101.9; 75.1; 70.7; 69.7; 38.9; 19.2; HRMS calcd for C18H26N2O6 (M)+ 366.1791, found 366.1792.

D. T. Gryko et al. / Tetrahedron: Asymmetry 9 (1998) 1771–1778
1777
3.9. (3aS,12aS)-2-Phenylperhydro[1,3]dioxolo[4,5f][1,4,9]-oxadiazacycloundecane-6,10-dione 13
Method A, yield 32%; [α]D23=+65.0 (c 1.0, DMSO); mp 283–285°C; δH (500 MHz, DMSO-d6): 7.95
(t, J=6.2, 1H); 7.87 (t, J=6.0, 1H); 7.5–7.3 (m, 5H); 5.86 (s, 1H); 4.0–3.9 (m, 6H); 3.6–3.2 (m, 4H);
δC (125 MHz, DMSO-d6): 169.3; 169.2; 136.9; 129.4; 128.2; 126.7; 101.9; 79.1; 77.6; 73.3; 73.2; 40.6;
40.2; HRMS calcd for C15H17N2O5 (M−H)+ 305.1137, found 305.1136.
3.10. (3aS,17aS)-2-Phenyl-3a,4,5,6,7,7,14,15,16,17,17a-decahydrobenzo[b][1,3]-dioxolo[4,5-i][1,4,7,
12]dioxadiazacyclotetradecane-6,15-dione 14
Method A, yield 20%; [α]D23=+18.9 (c 1.0, DMSO); mp 294–296°C; δH (200 MHz, DMSO-d6): 8.15
(bt, J=5.9, 1H); 8.06 (bt, J=5.8, 1H); 7.6–7.3 (m, 5H); 7.2–7.0 (m, 4H); 5.95 (s, 1H); 4.6–4.3 (m, 4H);
4.3–4.0 (m, 2H); 3.7–3.2 (m, 4H); δC (50 MHz, DMSO-d6): 168.2; 168.1; 148.6; 136.9; 129.5; 128.3;
126.8; 123.6; 123.4; 118.5; 118.1; 102.1; 79.2; 78.3; 70.7; 70.4; 41.3; 40.1; HRMS calcd for C21H22N2O6
(M)+ 398.1472, found 398.1472.
3.11. (3aS,9aS,12aS,18aS)-2-Phenyl-11,11-dimethylperhydrodi[1,3]-dioxolo[4,5-f:4,5-n][1,12,4,9]-
dioxa-diazacyclohexadecane-7,15-dione 15
Method B, yield 10%; method C, yield 49%; [α]D23=+42.4 (c 1.05, DMSO); mp 239–240°C; δH (500
MHz, DMSO-d6): 7.93–7.83 (q, J=6.2, 2H); 7.5–7.3 (m, 5H); 5.93 (s, 1H); 4.14 (m, 1H); 4.1–3.8 (m,
8H); 3.60 (m, 4H); 3.48 (m, 1H); 3.36 (m, 1H); 3.20 (m, 1H); 1.31 (s, 6H); δC (125 MHz, DMSO-d6):
169.3; 169.2; 138.0; 129.3; 128.3; 126.6; 108.7; 102.4; 78.6; 78.5; 76.2; 71.3; 71.2; 69.8; 69.7; 40.9;
39.1; 26.9; HRMS calcd for C22H30N2O8 (M)+ 450.2002, found 450.2000.
Acknowledgements
This work was supported by the State Committee for Scientific Research (Project 3T09A13409).
References
1. (a) Alexander, V. Chem. Rev. 1995, 95, 273–342. (b) Bastida, R.; de Blas, A.; Castro, P.; Fenton, D. E.; Macias, A.; Dial,
R.; Rodriguez, A.; Rodriguez Blas, T. J. Chem. Soc., Dalton. Trans. 1 1996, 1493–1497.
2. (a) Lindoy, L. F. The Chemistry of Macrocyclic Ligands Complexes; Cambridge University Press: Cambridge, 1989. (b)
Lehn, J.-M. Supramolecular Chemistry, VCH: Weinheim, 1995.
3. (a) Izatt, R. M .; Bradshaw, J. S.; Pawlak, K.; Bruening, R. L.; Tarbet, B. J. Chem. Rev. 1992, 92, 1261–1354. (b) Goodman,
M. S.; Rose, S. D. J. Org. Chem. 1992, 57, 3268–3270. (c) Kluger, R.; Tsao, B. J. Am. Chem. Soc. 1993, 115, 2089–2090.
4. (a) Dietrich, B.; Lehn, J.-M.; Sauvage, J. P. Tetrahedron 1973, 29, 1629–1645. (b) Bradshaw, J. S.; Krakowiak, K. E.;
Izatt, R. M. In Aza Crown Macrocycles; John Wiley & Sons: New York, 1993. (c) Krakowiak, K. E.; Bradshaw, J. S.;
Zamecka-Krakowiak, D. J. Chem. Rev. 1989, 89, 929–972.
5. (a) Jurczak, J.; Kasprzyk, S.; Sałan´ski, P.; Stankiewicz, T. J. Chem. Soc., Chem. Commun. 1991, 956–957. (b) Jurczak, J.;
Kasprzyk, S.; Sałan´ski, P.; Stankiewicz, T. High Press. Res. 1992, 11, 139–143. (c) Jurczak, J.; Stankiewicz, T.; Sałan´ski,
P.; Kasprzyk, S.; Lipkowski, P. Tetrahedron 1993, 49, 1478–1488.
6. (a) Fukada, N.; Ohtsu, T.; Miwa, M.; Mashino, M.; Takeda, Y. Bull. Chem. Soc. Jpn 1996, 69, 1397–1401. (b) Sharghi,
H.; Eshghi, H. Tetrahedron 1995, 51, 913–922. (c) Arnaud, N.; Picard, C.; Cazaux, L.; Tisnes, P. Tetrahedron 1997, 53,
13757–13768.
7. Gryko, D. T.; Pia˛tek, P.; Jurczak, J. Tetrahedron 1997, 53, 7957–7966.

1778
D. T. Gryko et al. / Tetrahedron: Asymmetry 9 (1998) 1771–1778
8. (a) Montanari, F.; Tundo, P. Tetrahedron Lett. 1979, 20, 5055–5058. (b) Rastetter, W. H.; Phillion, D. P. J. Org. Chem.
1981, 46, 3204–3208. (c) Curtis, W. D.; Laidler, D. A.; Stoddart, J. F.; Jones, G. H. J. Chem. Soc., Chem. Commun. 1975,
833–835.
9. Smith, K.; Morris, I. K.; Owen, P. G.; Bass, R. J. J. Chem. Soc., Perkin Trans. 1 1988, 77–83.
10. (a) Mitsunobu, O. Synthesis 1981, 1–28. (b) Hughes, D. L. Org. React. 1992, 42, 335–656. (c) Hughes, D. L. Org. Prep.
Proced. Int. 1996, 28, 127.
11. (a) Hoger, S. Synthesis, 1997, 20–22. (b) Voit, B. I.; Wolf, D. Tetrahedron 1997, 53, 15535–15551.
12. Lipshutz, B. H.; James, B.; Vance, S.; Carrico, I. Tetrahedron Lett. 1997, 38, 753–756.
13. (a) Mulzer, J.; Brand, C. Tetrahedron 1986, 42, 5961–5968. (b) Hegedus, L. S.; Holden, M. S.; McKearin, J. M. Org.
Synth. 1984, 62, 48.
14. Manhas, M. S.; Hoffman, W. H.; Lal, B.; Bose, A. K. J. Chem. Soc., Perkin Trans. 1 1975, 461–463.
15. Byun, H.-S.; Bittman, R. Synth. Commun. 1993, 23, 3201–3204.
16. Curtis, W. D.; Laidler, D. A.; Stoddart, J. F.; Jones, G. H. J. Chem. Soc., Perkin Trans. 1 1977, 1756–1769.
17. Carlock, J. T.; Mack, M. P. Tetrahedron Lett. 1978, 19, 5153–5156.
18. Jurczak, J.; Gryko, D. T. Organic Synthesis at High Pressure. In Chemistry under Extreme or Non-Classical Conditions;
van Eldik, R.; Hubbard, C. D., eds.; John Wiley & Sons and Spektrum Akademisher Verlag: New York, Heidelberg, 1997;
pp. 163–188.
19. Gryko, D. T.; Pia˛tek, P.; Jurczak, J. Synthesis, submitted.
20. Backer, H. J.; Stevens, W. Recl. Trav. Chim. Pays-Bas. 1940, 59, 423–444.