6-endo Versus 5-exo radical cyclization: streamlined syntheses of carbahexopyranoses and derivatives by 6-endo-trig radical cyclization

Article abstract of DOI:10.1016/j.tetlet.2006.12.108

Three factors that can direct 6-endo radical cyclization over 5-exo ring closure: substitution at C-5, vinyl radical cyclization and ring strain, have been considered in the context of the preparation of carbapyranoses from carbohydrate derivatives. As a

Full text of DOI:10.1016/j.tetlet.2006.12.108

Tetrahedron Letters 48 (2007) 1645–1649
6-endo Versus 5-exo radical cyclization: streamlined
syntheses of carbahexopyranoses and derivatives
by 6-endo-trig radical cyclization
*
´
´
Ana M. Gomez, Maria D. Company, Clara Uriel,
*
´
´
Serafın Valverde and J. Cristobal Lopez
Instituto de Quı´mica Orga´nica General, CSIC, Juan de la Cierva 3, 28006 Madrid, Spain
Received 23 November 2006; revised 14 December 2006; accepted 19 December 2006
Available online 23 December 2006
Abstract—Three factors that can direct 6-endo radical cyclization over 5-exo ring closure: substitution at C-5, vinyl radical
cyclization and ring strain, have been considered in the context of the preparation of carbapyranoses from carbohydrate derivatives.
As a result, alkyl radicals in substrates containing a strain inducing 2,3-O-isopropylidene ring, and vinyl radical in non-strained
compounds undergo a completely regioselective 6-endo-trig ring closure leading to carbasugar derivatives.
ꢀ 2007 Elsevier Ltd. All rights reserved.
Contrary to predictions based on thermodynamic crite-
ria, the cyclization of 5-hexenyl radicals (e.g., 1a) gener-
ally results in the formation of cyclopentane derivatives
(2a) via a predominant 5-exo mode of closure.1 This has
been rationalized in terms of stereoelectronic2 control of
the reaction and accordingly cyclohexane derivatives
(3a) arising from 6-endo closure are rarely observed.
Nevertheless, the regiochemistry of the radical cycliza-
tion can be influenced, and even reversed, to favor the
formation of six-membered rings by factors other than
stereoelectronic control.3
R
R
R
R
R
Bu3SnH
(a)
(b)
1
2
3
R
Bu3SnH
Bu3SnH
4
5
6
Three of the strategies used to favor 6-endo selectivity,
outlined in Scheme 1, are based on: (1) the substitution
pattern at C-5 (Scheme 1a). This result has been ascribed
to the presence of an unfavorable steric effect in the 5-
exo mode of cyclization.4 Accordingly, cyclization of
1b yields a 2:3 ratio of exo/endo products 2b/3b com-
pared to a 49:1 ratio for 2a/3a obtained from the cycli-
zation of 1a; (2) the vinylic nature of the radical (Scheme
1b). Beckwith5 and Stork6 have shown that under tin hy-
dride mediated reaction conditions, the radical cycliza-
tion of 1-vinyl-5-hexenyl radicals 4a gives mixtures of
both 5-exo and 6-endo products (5a and 6a). The kinetic
(c)
7
8
a
b
Series: , R = H; , R = Me
Scheme 1. 5-exo/6-endo Radical cyclization of different radicals.
studies of Beckwith also revealed that the formation of
methylene cyclohexane 6a is the result of further isomer-
ization of an initially formed ‘5-exo radical’,5 and
therefore low concentrations of stannane favor the
isomerization process leading to six-membered rings;
(3) the ring strain associated with intermediates such
as 7. Hoffmann and co-workers found that five-mem-
bered rings with two appendages, that contain a radical
Keywords: Radical cyclization; 6-endo-trig; 5-exo-trig; Carbasugars;
Carbasugar C-glycosides; Carbapyranoses.
*
Corresponding authors. Tel.: +34 915622900; fax: +34 915644853
(J.C.L.); e-mail addresses: anago@iqog.csic.es; clopez@iqog.csic.es
0040-4039/$ - see front matter ꢀ 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2006.12.108

1646
A. M. Go´mez et al. / Tetrahedron Letters 48 (2007) 1645–1649
derivatives 13 and 9 by deprotection (THF, AcOH,
O
O
O
O
H2O) followed by benzylation (NaH, BnBr) or acetyl-
ation, respectively. Alkenes 16–18 were prepared from
2,3:4,6-di-O-isopropylidene-D-gluco14 or D-manno13
pyranoses.
SnBu3
4
4
Bu3SnH
ref 8
O
O
O
O
10
9
The results obtained are outlined in Table 1. Treatment
of enyne 13 with Bu3SnH and AIBN in toluene (0.02 M,
85 ꢁC, syringe pump addition 6 h, then 12 h more)
resulted in the formation of epimeric alkenyl stannanes
19 and 20 as the sole observed regioisomers (Table 1,
entry 1). Enyne 14, under similar reaction conditions,
followed by destannylation (THF, AcOH, H2O), yielded
methylenecyclohexanes 21 and 22 (Table 1, entry 2).
Likewise, radical cyclization of tetraacetate 15 gave rise
to carbasugar precursors 23 and 24 (Table 1, entry 3).
Radical cyclizations of gluco-thionocarbonate 16 and
xanthate 17 took place with complete endo-selectivity
to yield carbasugar derivatives 25 and 26 (Table 1,
entries 4 and 5). On the contrary, radical cyclization of
manno-thionocarbonate 18 took place with complete
exo-selectivity to generate cyclopentane 27 (Table 1,
entry 6).
O
AcO
AcO
SnBu3
steps
4
O
4
OAc
OAc
O
O
AcO
OR
12
11
a, 4
b
, 4 =
Series:
=
OR
Scheme 2. Synthesis of carbasugars (12) by 6-endo-trig radical
cyclization of enynes (9).
and a radical acceptor, in an anti-disposition, undergo
6-endo closure, 7!8, rather than the potentially faster
5-exo cyclization which is prevented by ring strain7
(Scheme 1c).
In this context, some time ago,8 we reported a concise
entry to carbasugars (e.g., 12, Scheme 2),9 based on
the entirely regioselective 6-endo-trig radical cyclization
of enynes 9, followed by standard transformation of
the ensuing alkenyl stannanes (11) (Scheme 2). The suc-
cess of the key transformation (9!11) was largely based
on the above-mentioned regio-directing features. More
recently, we have shown that 1-vinyl-5-methyl-5-hexenyl
radicals 4b (Scheme 1b), which combine the vinylic nat-
ure of the radical and the substitution at C-5 as regiodi-
recting features, give rise to six-membered ring products
(6b) as the major isomers prevailing over the isomeric
five-membered ring compounds (5b).10
The stereochemistry at C-5 in compounds 19–26 was
unambiguously established based on the observed vici-
nal coupling constants (e.g., J4,5). For instance, the
assignment of the stereochemistries at C-1 and C-5 in
compound 26 was made as follows: the axial nature
for H-2 and the b-configuration for the methyl group
at C-1 were inferred from the observed coupling con-
stants, J1,2 and J2,3 (8.7 and 9.0 Hz, respectively). Other
observed coupling constants: J3,4 = 9.0 and J4,5
=
4
9.0 Hz, allowed us to propose a C1 conformation for
26, and a b-configuration for the hydroxymethyl group
at C-5 (D-series). The stereochemistry at the quaternary
center in compound 27 was rigorously assigned on the
basis of an observed NOE between H-4 and the methyl
group.
The nature of our original strategy restricted its use to
enynes containing the required strain-inducing 2,3-anti-
isopropylidene group (e.g., 9a,b). For that reason, we
have recently turned our attention to the relative impor-
tance of the factors dictating the regiochemical outcome
of this radical cyclization, and in this Letter we disclose
a general approach to carbapyranoses based on the
regioselective 6-endo-trig cyclization of more simple
sugar precursors.
From the results in Table 1, some conclusions can be
inferred. Substrates that incorporate two regiodirecting
features: (a) vinyl radical and substitution at C-5 (com-
pounds 13–15, Table 1 entries 1–3) or (b) ring strain and
substitution at C-5 (compounds 16 and 17, Table 1,
entries 4 and 5) undergo 6-endo-trig radical cyclization.
However, thionoformate 18, where the substituent at
C-5 was the only regiodirecting factor, underwent 5-
exo-trig ring closure exclusively. On the other hand,
the bicyclic nature of enyne 13 or the linear nature of
14 do not seem to influence the regiochemistry of the
process, although they do have a profound influence
on its stereoselectivity (Table 1, compare entries 1 and
2). The radical cyclization of enyne 14 is noteworthy
since no competing intramolecular hydrogen transfer
(e.g., 1,5-H) from the benzyl groups was observed. A
primary, rather than a vinyl, radical ensuing from Bar-
ton–McCombie type deoxygenation of thionocarbonate
16 also underwent an efficient cyclization to yield 1-
deoxy-5a-carba-D-glucopyranose derivative 25, which
for the purpose of characterization was transformed
into its corresponding tetra-O-acyl derivative. Deoxy-
genation of secondary xanthate 17, was also followed
As candidates for our study, we have prepared manno-
and gluco-derivatives 13–18. manno-Derivative 13 was
chosen because it was devoid of the 2,3-anti-isopropylid-
ene ring, and so were acyclic enynes 14 and 15. Thiono-
carbonate11 16 and xanthate12 17 were selected because
while maintaining the 2,3-anti-isopropylidene ring
would generate intermediate alkyl, rather than vinyl,
radicals. Finally, thionocarbonate 18, that retains only
the substitution pattern at C-5 as a regiodirecting factor,
was also prepared.
Enyne 13 was synthesized, following our described
methodology for the preparation of 9, starting from
2,3:4,6-di-O-isopropylidene-D-manno pyranose.13 Eny-
nes 14 and 15 were prepared from di-O-isopropylidene

A. M. Go´mez et al. / Tetrahedron Letters 48 (2007) 1645–1649
1647
Table 1. Radical cyclization of carbohydrate derivatives 13–18 mediated by Bu3SnH and AIBN
Entry
Starting material
Products
Yield (%)
O
O
O
O
5
5
SnBu3
SnBu3
1
64a
O
O
2
O
O
O
O
O
O
(15:1)
19
20
13
BnO
BnO
BnO
BnO
BnO
BnO
5
5
2
2
80a,b
BnO
14
OBn
BnO
OBn
BnO
OBn
21
(1.6:1)
22
AcO
AcO
AcO
15
AcO
AcO
AcO
AcO
5
5
2
3
64a,b
OAc
AcO
OAc
AcO
OAc
(1.4:1)
23
24
O
O
O
OPh
S
O
O
2
4
62a
O
O
O
O
25
16
17
O
O
O
O
SCH3
5
S
1
CH3
2
5
64a
O
O
O
O
O
26
nOe
CH3
O
O
O
OPh
S
H4
O
O
2
6
76a
O
O
O
O
18
27
Reaction conditions: (a) Bu3SnH, AIBN, 0.02 M (initial concentration of the substrate), toluene, 85 ꢁC, syringe pump addition; (b) THF, AcOH,
H2O (4:2:1), room temperature.
by radical cyclization to yield, in stereoselective manner,
carbapyranose C-glycoside derivative 26. However, dif-
ferent radical precursors related to 17 where the methyl
groups at C-1 have been replaced by n-butyl, allyl or
alkynyl groups did not lead, upon similar treatment with
Bu3SnH and AIBN, to synthetically useful amounts of
the expected carbasugar C-glycosides.15
must include at least one regiodirecting feature (vinyl
radical or ring strain) in addition to the ‘substitution
at C-5’. The method allows the synthesis of carbapyra-
nose exo-glycals16,17 (e.g., 21–24) and has also been pro-
ven useful in the preparation of a methyl C-glycoside of
a carbasugar, 26.18–20
In summary, we have found that simple unsaturated car-
bohydrate systems are able to undergo 6-endo-trig radi-
cal cyclization leading to carbapyranose derivatives.
These systems have been rationally devised and they
Acknowledgements
This research has been supported with funds from the
´
Direccion General de Ensenanza Superior (Grant
˜

1648
A. M. Go´mez et al. / Tetrahedron Letters 48 (2007) 1645–1649
´
´
´
14. Gomez, A. M.; Danelon, G. O.; Valverde, S.; Lopez, J. C.
PPQ-2003-00396). M.D.C. thanks the Comunidad de
Madrid for a scholarship and C.U. thanks the Consejo
Carbohydr. Res. 1999, 320, 138–142.
15. These cyclization reactions led to complex reaction
mixtures that included the corresponding deoxygenated
compounds and minor amounts of stereoisomeric
cyclized products. For instance, from the reaction of
the allyl analogue of methyl xanthate 17 we could isolate
a compound resulting from deoxygenation (23%) as well
as two isomeric C-allyl carbasugars (6% and 10%
yield).
´
Superior de Investigaciones Cientıficas for financial
support.
References and notes
1. (a) For leading references, see: Curran, D. P.; Porter, N.
A.; Giese, B. Stereochemistry of Radical Reactions-Con-
cepts. Guidelines and Synthetic Applications; Weinheim,
Germany, 1996; (b) Fossey, J.; Lefort, D.; Sorba, J. Free
Radicals in Organic Chemistry; John Wiley and Sons:
Chichester, England, 1995; (c) Beckwith, A. L. J. Chem.
Soc. Rev. 1993, 22, 143–151; (d) RajanBabu, T. V. Acc.
Chem. Res. 1991, 24, 139–145; (e) Giese, B. Angew. Chem.,
Int. Ed. Engl. 1983, 22, 753–764; (f) Julia, M. Acc. Chem.
Res. 1971, 4, 386–392; (g) Giese, B. Radicals. In Organic
Synthesis: Formation of Carbon Carbon Bonds; Baldwin,
J. E., Ed.; Pergamon: New York, 1986.
16. For reviews on exo-glycals, see: (a) Taillefumier, C.;
Chapleur, Y. Chem. Rev. 2004, 104, 263–292; (b) Taylor,
R. J. K. Chem. Commun. 1999, 217–227.
´
´
17. (a) Gomez, A. M.; Pedregosa, A.; Valverde, S.; Lopez, J.
´
C. Chem. Commun. 2002, 2022–2023; (b) Gomez, A. M.;
´
´
Danelon, G. O.; Pedregosa, A.; Valverde, S.; Lopez, J. C.
´
Chem. Commun. 2002, 2024–2025; (c) Gomez, A. M.;
´
Pedregosa, A.; Valverde, S.; Lopez, J. C. Tetrahedron Lett.
´
2003, 44, 6111–6116; (d) Gomez, A. M.; Pedregosa, A.;
´
Barrio, A.; Valverde, S.; Lopez, J. C. Tetrahedron Lett.
´
2004, 45, 6307–6310; (e) Gomez, A. M.; Barrio, A.;
´
2. Beckwith, A. L. J. Tetrahedron 1981, 37, 3073–3100, and
references cited therein.
Amurrio, I.; Jarosz, S.; Valverde, S.; Lopez, J. C.
Tetrahedron Lett. 2006, 47, 6243–6246.
3. For selected references, see: (a) Ishibashi, H. Chem. Rec.
2006, 6, 23–31; (b) Della, E. W.; Graney, S. D. J. J. Org.
Chem. 2004, 69, 3824–3835; (c) Cassayre, J.; Gagosz, F.;
Zard, S. Z. Angew. Chem., Int. Ed. 2002, 41, 1783–1785;
(d) Della, E. W.; Kostakis, Ch.; Smith, P. A. Org. Lett.
1999, 1, 363–365; (e) Ward, D. E.; Gai, Y.; Kaller, B. F. J.
Org. Chem. 1995, 60, 7830–7836; (f) Keusenkothen, P. F.;
Smith, M. B. Tetrahedron 1992, 48, 2977–2992; (g) Marco-
Contelles, J.; Bernabe, M.; Ayala, D.; Sanchez, B. J. Org.
Chem. 1994, 59, 1234–1235; (h) Ward, D. E.; Kaller, B. F.
Tetrahedron Lett. 1991, 32, 843–846; (i) Knapp, S.;
Gibson, F. S.; Choe, Y. H. Tetrahedron Lett. 1990, 31,
5397–5400; (j) Padwa, A.; Nimmesgern, H.; Wong, G. S.
K. J. Org. Chem. 1985, 50, 5620–5627.
4. (a) Beckwith, A. L. J.; Blair, I. A.; Philipou, G. Tetra-
hedron Lett. 1974, 15, 2251–2254; (b) Beckwith, A. L. J.;
Lawrence, T. J. Chem. Soc., Perkin Trans. 2 1979, 1535–
1539.
5. Beckwith, A. L. J.; O’Shea, D. M. Tetrahedron Lett. 1986,
27, 4525–4528.
18. General procedure for the radical cyclization: A thoroughly
degassed solution of the substrate (1 mmol) in toluene
(0.02 M) was heated at 80 ꢁC under argon. A solution of
Bu3SnH (1.5 equiv) and AIBN (0.3 equiv) was then added
in toluene (3 mL) via a syringe driven pump over 6 h.
Heating was then continued for 12 h. After cooling, the
reaction mixture was concentrated in vacuo and the
residue was purified by flash chromatography (hexane–
EtOAc 97.5:2.5).
19. General procedure for destannylation: The crude reaction
mixture from the above radical cyclization was dissolved
in a mixture of AcOH–THF–H2O (2:4:1) (50 mL) and
heated to reflux overnight. The solvent was then evapo-
rated and the methylene cyclohexanes were purified by
flash chromatography (hexane–ethyl acetate).
20. Data for selected compounds: Enyne 13: [a]D ꢀ40.0 (c 0.92,
CHCl3); 1H NMR (300 MHz, CDCl3): d (ppm) 1.35 (s,
3H), 1.42 (s, 3H), 1.46 (s, 3H), 1.56 (s, 3H), 2.54 (d,
J = 2.2 Hz, 1H), 4.27 (dd, J = 1.4, 14.2 Hz, 2H), 4.37 (t,
J = 6.0 Hz, 1H), 4.70 (m, 1H), 4.84 (dd, J = 6.0, 2.1 Hz,
1H), 4.97 (br s, 2H); 13C NMR (50 MHz, CDCl3): d (ppm)
23.0, 26.0, 27.0, 27.3, 53.4, 64.2, 67.4, 71.6, 78.0, 79.4,
100.1, 108.6, 110.8, 142.8, 177.0. Enyne 14: [a]D ꢀ59.6 (c
6. Stork, G.; Mook, R., Jr. Tetrahedron Lett. 1986, 27, 4529–
4532.
7. Albrecht, U.; Wartchow, R.; Hoffmann, H. M. R. Angew.
Chem., Int. Ed. Engl. 1992, 31, 910–913.
1
0.3, CHCl3); H NMR (300 MHz, CDCl3): d (ppm) 2.40
´
´
´
(d, J = 3.0 Hz, 1H), 3.77 (t, J = 5.3 Hz, 1H), 3.85 (d,
J = 12.0 Hz, 1H), 3.94 (d, J = 12.0 Hz, 1H), 4.19 (dd,
J = 11.6, 4.4 Hz, 1H), 4.29 (dd, J = 5.6, 2.0 Hz, 1H), 4.36–
4.85 (m, 8H), 5.30 (br s, 2H), 7.19–7.36 (m, 20H); 13C
NMR (50 MHz, CDCl3): d (ppm) 69.8, 75.3, 81.0, 81.8,
70.3, 70.6, 71.2, 72.7, 75.1, 116.8, 127.4 (·2), 127.5 (·4),
127.8 (·2), 127.9 (·2), 128.0 (·2), 128.2 (·4), 128.3 (·4),
137.8, 138.2, 138.3, 138.5, 142.5; API-ES positive: 555.5
(M+Na)+. Enyne 15: [a]D +46.9 (c 1.02, CHCl3); 1H NMR
(300 MHz, CDCl3): d (ppm) 2.09 (s, 3H), 2.12 (s, 3H), 2.13
(s, 6H), 2.56 (d, J = 2.0 Hz, 1H), 4.57 (d, J = 13.2 Hz,
1H), 4.71 (d, J = 13.2 Hz, 1H), 5.31 (d, J = 14.0 Hz, 1H),
5.48 (dd, J = 3.6, 7.0 Hz, 1H), 5.57 (dd, J = 2.0, 7.0 Hz,
1H), 5.67 (d, J = 3.6 Hz, 1H); 13C NMR (50 MHz,
CDCl3): d (ppm) 20.6, 20.8, 20.9, 21.0, 29.0, 62.9, 64.4,
72.0, 72.1, 76.3, 80.9, 81.6, 111.7, 118.3, 139.1, 169.5 (·2),
170.6 (·2); API-ES positive: 363.3 (M+Na)+, 358
(M+NH4)+. Methylene cyclohexanes 19: (4:1 mixture of
unassigned Z, E stannanes); 1H NMR (300 MHz, CDCl3):
d (ppm) 0.87 (t, J = 7.2, 9H), 0.89 (m, 6H), 1.24 (m, 6H),
1.27 (s, 3H), 1.29 (s, 3H), 1.30 (m, 6H), 1.31 (s, 3H), 1.33
(s, 3H), 1.91 (dd, J = 2.9, 10.4 Hz, 1H), 2.12 (m, 2H), 3.62
8. Gomez, A. M.; Danelon, G. O.; Valverde, S.; Lopez, J. C.
J. Org. Chem. 1998, 63, 9626–9627.
9. For reviews on carbasugars, see: (a) Sollogoub, M.; Sinay,
¨
P. In The Organic Chemistry of Sugars; Levy, D. E.,
Fugedi, P., Eds.; CRC Press: Boca Raton, 2006, Chapter
¨
8; (b) Kobayashi, Y. In Glycoscience. Chemistry and
Chemical Biology; Fraser-Reid, B., Tatsuta, K., Thiem, J.,
Eds.; Springer: Berlin, 2001; Vol. 3, Chapter 10.3; (c)
Ogawa, S. In Carbohydrate Mimics: Concepts and Meth-
ods; Chapleur, Y., Ed.; Wiley-VCH: Weinheim, 1998; pp
87–106; (d) Suami, T.; Ogawa, S. Adv. Carbohydr. Chem.
Biochem. 1990, 48, 21–90; (e) Ogawa, S. In Carbohydrates
in Drug Design; Witczak, Z. J., Nieforth, K. A., Eds.;
Marcel Dekker: New York, 1997; pp 433–469; (f) Suami,
T. Top. Curr. Chem. 1990, 154, 257–283.
´
10. Gomez, A. M.; Company, M. D.; Uriel, C.; Valverde, S.;
´
Lopez, J. C. Tetrahedron Lett. 2002, 43, 4997–5000.
11. Robins, M. J.; Wilson, J. S.; Hansske, F. J. Am. Chem.
Soc. 1983, 105, 4059–4065.
12. Barton, D. H. R.; McCombie, S. W. J. Chem. Soc., Perkin
Trans. 1 1975, 1574–1585.
13. Gelas, J.; Horton, D. Carbohydr. Res. 1978, 67, 371–387.

A. M. Go´mez et al. / Tetrahedron Letters 48 (2007) 1645–1649
1649
(t, J = 8.5 Hz, 1H), 3.75 (m, 2H), 4.12 (dd, J = 4.3, 5.9 Hz,
1H), 4.58 (d, J = 4.3 Hz, 1H), 6.12 (s, 1H); 13C NMR
(50 MHz, CDCl3): d (ppm) 10.0 (·3), 13.5 (·3), 26.1, 27.0,
27.1 (·3), 28.2, 28.9 (·3), 29.5, 32.3, 35.7, 64.0, 74.7, 79.2,
81.3, 98.9, 109.3, 133.4, 148.2; MS: 544 (M+1)+. Methyl-
ene cyclohexanes 20: (one isomer) 1H NMR (200 MHz,
CDCl3): d (ppm) 0.87 (m, 9H), 0.89 (m, 6H), 1.24 (m, 6H),
1.27 (s, 3H), 1.28 (s, 3H), 1.29 (m, 6H), 1.33 (s, 3H), 1.35
(s, 3H), 2.02 (m, 1H), 2.61 (m, 2H), 3.54 (dd, J = 2.2,
11.5 Hz, 1H), 4.00 (m, 3H), 4.43 (d, J = 7.1 Hz, 1H), 5.91
(s, 1H); 13C NMR (50 MHz, CDCl3): d (ppm) (one isomer)
10.2 (·3), 13.5 (·3), 26.5, 27.0 (·3), 28.9 (·4), 29.4, 29.6,
34.9, 36.4, 68.2, 75.1, 79.5, 79.5, 81.3, 99.0, 109.3, 133.4,
148.0; MS: 544 (M+1)+. Carbasugar derived exo-glycals 23
3.65 (m, 6H); 13C NMR (50 MHz, CDCl3): d (ppm) 19.3,
22.3, 26.8, 27.4, 29.7, 30.6, 39.4, 64.4, 73.8, 75.4, 78.3, 99.0,
110.6. It was characterized as its corresponding tetra-O-
acetyl derivative: [a]D +18.6 (c 0.14, CHCl3); 1H NMR
(300 MHz, CDCl3): d (ppm) 1.87 (m, 1H), 1.96 (m, 1H)
2.00 (s, 6H), 2.01 (s, 3H), 2.02 (s, 3H), 2.15 (m, 1H), 3.94
(dd, J = 3.4, J = 9.0 Hz, 1H), 4.05 (dd, J = 5.0, 9.0 Hz,
1H), 4.88 (m, 1H), 4.96 (t, J = 9.6, 1H), 5.07 (t, J = 9.6,
1H); 13C NMR (50 MHz, CDCl3): d (ppm) 15.2, 20.7,
23.5, 28.4, 29.7, 40.2, 43.9, 63.6, 71.8, 72.2, 75.0, 170.1,
170.2 (·2), 171.0; API-ES positive: 353 (M+Na)+. Carba-
1
sugar 26: [a]D ꢀ8.4 (c 0.2, CHCl3); H NMR (300 MHz,
CDCl3): d (ppm) 1.41 (s, 12H), 1.48 (s, 3H), 1.53 (m, 1H),
1.60 (m, 1H), 1.74 (m, 1H), 1.88 (m, 1H), 3.04 (dd, J = 9.0,
8.8 Hz, 1H), 3.44 (t, J = 9.0 Hz, 1H), 3.71 (m, 3H); 13C
NMR (50 MHz, CDCl3): d (ppm) 17.5, 26.8 (·2), 27.8
(·2), 32.5, 34.2, 39.0, 64.4, 73.9, 80.3, 83.7, 99.9, 110.9;
API-ES positive: 535 (2M+Na)+, 279 (M+Na)+. Cyclo-
pentane 27: 1H NMR (300 MHz, CDCl3): d (ppm) 1.07 (s,
3H), 1.27 (s, 3H), 1.32 (s, 3H), 1.38 (s, 3H), 1.48 (s, 3H),
1.59 (d, J = 14.4 Hz, 1H), 2.38 (dd, J = 14.4, 6.3 Hz, 1H),
3.40 (t, J = 12.0 Hz, 1H), 3.60 (d, J = 12.0 Hz, 1H), 3.94
(s, 1H), 4.37 (d, J = 6.0 Hz, 1H), 4.77 (t, J = 6.3 Hz, 1H);
13C NMR (50 MHz, CDCl3): d (ppm) 18.6, 21.7, 23.1,
25.5, 29.1, 38.9, 39.4, 66.7, 80.1, 80.7, 87.0, 97.4, 109.8;
API-MS positive: 265 (M+Na)+.
1
and 24 (mixture): H NMR (300 MHz, CDCl3): d (ppm)
1.68 (m, 2H), 2.02 (m, 1H), 2.03 (s, 3H), 2.04 (s, 3H), 2.04
(s, 3H), 2.06 (s, 3H), 2.08 (s, 3H), 2.09 (s, 3H), 2.11 (s, 3H),
2.13 (s, 3H), 2.16 (m, 2H), 2.52 (m, 2H), 4.02 (m, 3H), 4.09
(dd, J = 5.0, 11.6 Hz, 1H), 4.24 (dd, J = 5.0, 10.6 Hz, 1H),
5.10 (m, 7H), 5.91 (m, 2H); 13C NMR (50 MHz, CDCl3): d
(ppm) 20.4 (·2), 20.5, 20.6 (·2), 20.7, 20.8 (·2), 26.7, 27.8,
31.0, 33.0, 36.3, 40.1, 61.6, 63.2, 71.2, 71.4, 71.5, 72.9, 73.1,
74.9, 110.1, 113.2, 137.7, 139.2, 169.8, 169.9, 170.0, 170.1,
170.5 (·2), 170.6, 170.8; API-ES: 365 (M+Na)+. Carba-
1
sugar 25: [a]D ꢀ5.6 (c 0.7, CHCl3); H NMR (200 MHz,
CDCl3): d (ppm) 1.43 (s, 6H), 1.44 (s, 6H), 2.1 (m, 4H),