Synthesis of monoprotected 1,4-diketones by photoinduced alkylation of enones with 2-substituted-1,3-dioxolanes

Article abstract of DOI:10.1016/S0040-4020(01)01058-4

Photosensitized hydrogen abstraction from 2-alkyl-1,3-dioxolanes by triplet benzophenone gives the corresponding 1,3-dioxolan-2-yl radicals and these are trapped by α,β-unsatured ketones yielding monoprotected 1,4-diketones. With open chain ketones (3-buten-2-one and 4-penten-3-one) the yields are low and competitive pathways in part consume the radicals. With cyclic enones however, yields are good as tested with cyclopentenone, cyclohexenone and 4-hydroxy-cyclopentenone. More generally, this is a viable alternative for the synthesis of 1,4-diketones via radicals while the thermal initiation gives only low yield. The reaction cannot be extended to strongly stabilized radicals, such as the 2-phenyl-1,3-dioxolanyl radical.

Full text of DOI:10.1016/S0040-4020(01)01058-4

TETRAHEDRON
Pergamon
Tetrahedron 57 -2001) 10319±10328
Synthesis of monoprotected 1,4-diketones by photoinduced
alkylation of enones with 2-substituted-1,3-dioxolanes
Raffaella Mosca, Maurizio Fagnoni,p Mariella Mella and Angelo Albini
Á
Dipartimento di Chimica Organica, Universita, V. Taramelli 10, 27100 Pavia, Italy
Received 24 July 2001; revised 26 September 2001; accepted 18 October 2001
AbstractÐPhotosensitized hydrogen abstraction from 2-alkyl-1,3-dioxolanes by triplet benzophenone gives the corresponding 1,3-dioxo-
lan-2-yl radicals and these are trapped by a,b-unsatured ketones yielding monoprotected 1,4-diketones. With open chain ketones -3-buten-2-
one and 4-penten-3-one) the yields are low and competitive pathways in part consume the radicals. With cyclic enones however, yields are
good as tested with cyclopentenone, cyclohexenone and 4-hydroxy-cyclopentenone. More generally, this is a viable alternative for the
synthesis of 1,4-diketones via radicals while the thermal initiation gives only low yield. The reaction cannot be extended to strongly
stabilized radicals, such as the 2-phenyl-1,3-dioxolanyl radical. q 2001 Elsevier Science Ltd. All rights reserved.
1. Introduction
compounds with a cyclopentan-en)one structure such as
prostaglandins, jasmonoids, pentenomycins and cyclopenta-
noid antibiotics as well as of various heterocycles -e.g.
furans, pyrroles, thiophenes and pyridazines)4 gave impetus
to this study, aimed to explore whether a photoinduced
radical alkylation based upon non-toxic and inexpensive
reagents could afford a viable alternative.
Recently we reported a mild procedure for the synthesis of
monoprotected 1,4-ketoaldehydes by introducing a 1,3-
dioxolanyl group onto a,b-unsatured ketones.1 In view of
the versatility of the 1,3-dioxolanyl moiety, which not only
is a removable protecting group but is also directly con-
vertible into other functionalities,2 itappeared worhtwhile
to test the scope of the method. The synthesis of more
heavily functionalized 4-ketoaldehydes, as well as of
several monoprotected 1,4-diketones starting from 2-alkyl-
1,3-dioxolanes is reported. Apart from partial protection of
diketones, which usually gives a mixture,3a monoprotected
1,4-diketones have been previously obtained through multi-
step syntheses, viz. via g-oxosulfones ketals,3b by acylation
of organonickel complexes,3c from g-nitroketal deriva-
tives3d or by oxidation of g-hydroxyketals.3e This factand
the major role 1,4-diketones have for the synthesis of natural
2. Results
The radical precursors considered in the present study were
1,3-dioxolanes bearing different alkyl substituents in
position 2, methyl -compound 2k), ethyl -2l), branched
-2-methylpropyl, 2m) and a long chain -n-hexyl, 2n). An
aromatic 1,3-dioxolane -2-phenyl-1,3-dioxolane, 2o) was
also considered -see Scheme 1).
Scheme 1.
Keywords: alkylation; radicals and radical reactions; 1,4-diketones; photochemistry; prostanoids.
Corresponding author. Tel.: 139-382507316; fax: 139-382507323; e-mail: fagnoni@chi®s.unipv.it
p
0040±4020/01/$ - see front matter q 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020-01)01058-4

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R. Mosca et al. / Tetrahedron 57 '2001) 10319±10328
Table 1. Alkylation yields from a,b-unsatured ketones and dioxolanes 2
Entry
Ketone
Dioxolane
Products
Reactions conditions -time, h)
Product yield -%)a
1
2
3
4
5
6
7
8
1a
1a
1a
1a
1a
1a
1a
1b
1c
1c
1c
1c
1d
1d
1d
8
2k
2kb
2k
2l
2m
2n
2o
2l
3ak
3ak
3ak
3al
3am
3an
4o, 5o, 6, 7
3bl
3ck
3cl
3cn
hn -2.5)
hn -2.5)
Dd
28
49c
,3c,d
28
hn -2.5)
hn -2.5)
hn -15)
hn -4)
hn -2.5)
hn -2.5)
hn -2.5)
hn -2.5)
hn -4)
hn -7)
Dd
hn -7)
hn -2)
hn -2)
hn -4)
hn -2)
32
,5c
e
21
78
70
9
2k
2l
10
11
12
13
14
15
16
17
18
19
2n
2o
2k
2k
2n
2k
2p
2p
2p
68
e
4o, 5o, 6, 7
3dk
3dk
48
21c,d
57
3dn
9k/9k0 -11/1)f, 10
9p/9p0 -2.2/1)f
9p/9p0 -6/1)f
13, 130
75, 7.2
74
8
8
12
60g
46, 22
a
Isolated yield.
Neatdioxolane 2k as the solvent.
GC yield.
Thermal reaction. See Text.
No alkylation occurred. See Text.
Mixture of diastereoisomer -trans as the main isomer).
b
c
d
e
f
g
Reaction in aqueous medium.
2.1. Alkylation of open chain a,b-unsatured ketones
solution of the starting ketone -0.05 M) in a 1 M solution of
the dioxolane 2 in acetonitrile in the presence of benzophe-
none as the sensitizer -0.02 M). Preliminary experiments
have shown that no alkylation occurred in the absence of
the sensitizer.
The photochemical alkylation was ®rst tested on two repre-
sentative open chain unsatured ketones, 3-buten-2-one -1a)
and 1-penten-3-one -1b). Irradiations were carried out on a
Scheme 2.

R. Mosca et al. / Tetrahedron 57 '2001) 10319±10328
10321
Scheme 3.
Under these conditions, on using 1,3-dioxolanes 2k, 2l and
2m as radical precursors enone 1a was alkylated and satu-
rated ketones 3 were obtained, but the isolated yields were
low -21±28%, see Table 1, entries 1, 4, 5). A higher yield of
3ak resulted when the alkylation of 1a was carried outin
neat 2k -49%, entry 2) accompanied by a relevant amount of
4a. With 2-hexyl-1,3-dioxolane 2n, the formation of only a
small amountof alkylaetd 3an was demonstrated by GC/
MS. Some byproducts arising from alternative decomposi-
tion pathways of dioxolane 2n were detected in this case,
viz. b-hydroxyethyl heptanoate 4n and ethyl heptanoate 5n
-Scheme 2). The results with enone 1b were analogous and
alkylated ketone 3bl was formed from 2l in a somewhat
lower yield than 3al -21%).
2-hydroxyethyl benzoate -4o), ethyl benzoate -5o), 1,1-di-
phenyl--2-phenyl-1,3-dioxolan-2-yl)-methanol -6) and
2,20-diphenyl-[2,20]bis-1,3-dioxolanyl -7) -see Scheme 3).
2.2. Cyclic a,b-unsatured ketones
More satisfactory results were obtained with ®ve- and six-
membered enones. In particularly, 3-alkylcyclopentanones
3ck, l, n were obtained in a high yield -.70%) in a short
irradiation time -2.5 h) from cyclopentenone and the corre-
sponding 2-substituted-1,3-dioxolanes. The reaction could
not be extended to dioxolane 2o, however. Similar to the
reaction of 1a, in the last case only products resulting from
alternative reactions of dioxolane were obtained. The alkyl-
ation of cyclohexenone -1d) was also successful, with a
reasonable yield of products 3dk and 3dn -48 and 57%,
Alkylation was unsuccessful with dioxolane 2o. In this case,
several dioxolane derived products were identi®ed, viz.
Scheme 4. a. Overall yields based on starting cyclopentenone 8.

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R. Mosca et al. / Tetrahedron 57 '2001) 10319±10328
Scheme 5.
respectively). Cycloheptenone -1e) on the other hand, was
consumed but was not alkylated under these conditions.
3. Discussion
The present synthesis involves the alkylation of electro-
philic alkenes by dioxolanyl radicals. Previous attempts to
generate such radicals by thermal hydrogen abstraction have
met only a limited success. Decomposition of peroxides in
the presence of 1,3-dioxolanes and ole®ns led to some alkyl-
ation, in particular with electron-withdrawing substituted
alkenes but side-reactions such as cleavage to ethyl esters
-see later) or, in some cases, polymerization consumed most
of the radicals.5,6 Better results were reported employing
di-t-butyl-hyponitrite -DBH) as a radical initiator which
has the advantage of an easier work up -the initiator gives
rise to volatile byproducts) but its application is limited due
to the non-trivial synthesis of the initiator.7 Indeed attempts
to use dioxolanes in thermally initiated radical alkylation
were also carried outduring presentwork -Table 1, enrties
3, 14) and the yields were low.
In view of the success with ®ve- and six-membered ring
enones, the reaction was extended to 4-hydroxy-cyclo-
pentenone 8. The reaction with 2k yielded 9k -trans
isomer) as the main product besides a minor amount of
the cis isomer -9k0) -74.2%, overall alkylation yield;
trans/cis 11/1, Scheme 4) as well as a small amountof
a doubly alkylated product, all trans 4-hydroxy-2--hydroxy-
diphenyl-methyl)-3--2-methyl-1,3-dioxolan-2-yl)-cyclo-
pentanone 10 -7%). The crude 9k/9k0 mixture was easily
transformed into cyclopentenone 11k -40%, one pot
synthesis from 8) through the intermediacy of the corre-
sponding methansulfonate.
The same alkylation±elimination procedure was applied to
the reaction with 8 and 1,3-dioxolane -2p) as the radical
precursor. Again, a mixture of trans -9p) and cis -9p0)
isomers was obtained, although attack was less stereoselec-
tive -trans/cis 2.2/1). As in the previous case, the isomer
mixture was easily transformed into enone 11p.
Photochemical initiation was generally more effective.8 The
mechanism is reported in Scheme 2. Excitation of benzo-
phenone to the triplet state is followed by hydrogen abstrac-
tion from dioxolanes 2 yielding the corresponding dioxolan-
2-yl radicals 2. Substitution in position 2 does not hinder
this step. Stereoelectronic factors remain favorable, and
Ingold has shown that the rate of hydrogen abstraction
from such derivatives is only slightly lower than with the
parent1,3-dioxolanes. 9a A practical limitation for the exten-
sion of the method is that the elimination of excess reagent
is cumbersome with high boiling dioxolanes; this limits the
concentration of dioxolanes used. Yields are somewhat
lower in dilute solutions of dioxolanes 2 rather than in the
neat reagent -compare entries 1 and 2). Nevertheless a lower
concentration of alkyldioxolanes as the hydrogen donors led
to a simpler products mixture -see Section 5).
It was explored whether the selectivity in the formation of
the trans isomer 9p with respect to 9p0 was improved when
the OH group was substituted by a bulky t-butyldiphenyl-
silyloxy group. However, there were no appreciable
advantages in this direction, except for the fact that both
of the isomers -13, trans and 130, cis) were easily isolated
by silica gel chromatography -overall yield 68%, Scheme
5). A marked improvement of the selectivity -from 2.2/1 to
6/1) was achieved carrying out the reaction on enone 8
in mixed dioxolane±water solution. In this case a water-
soluble sensitizer such as benzophenone sodium sulfonate
was used -see Section 5 and entry 18 in Table 1).
The radicals are trapped by the ole®ns present in solution -1,
8, 12, path a) and the resulting adduct radicals give rise to
the ®nal 1,4-monoprotected dioxolanyl derivatives -3, 9, 13)
through hydrogen abstraction. The latter process involves
hydrogen transfer from the solvent -path d), the dioxolane
-path e)9b or the ketyl radical intermediate -path f ). The ®rst
path -path d) yields benzopinacol -14) as a sideproduct, but
the last two allow the use of benzophenone in a less than
stoichiometric amount -we used 40%, see Section 5).
2.3. Alkylation by thermal radical chain method
It was obviously important to compare the above photo-
chemical alkylations of enones with thermal initiated reac-
tions. Therefore we also tested the synthesis of compound 3
by generating 1,3-dioxolanyl radicals by thermal radical
initiators, viz. AIBN and benzoyl peroxide. No detectable
alkylated ketone 3ak was obtained from 1a and 2k with
AIBN and only a small amount- ,3%) with benzoyl perox-
ide. -Table 1, entry 3). The last initiator gave a better yield
with 1d as the starting ketone -21%, 3dk, see Section 5 and
Table 1 entry 14). We could not improve the thermal alkyl-
ation beyond these limits.
The overall yield of the alkylation process depends pri-
marily on the ef®cient trapping of radical 2z with respect
to competitive paths. Among these, the ®rst one is the
above mentioned5 rearrangement to ethylesters 5 via the

R. Mosca et al. / Tetrahedron 57 '2001) 10319±10328
10323
open chain 2-oxycarbonyl radicals -path b), while the
second involves oxidation of 2z to the corresponding cation
followed by water assisted opening to give 2-hydroxyethyl-
esters 4 -path c). The oxidizing agentis probably benzo-
phenone ground state.10
chemistry is observed -Table 1, entries 16±18).18 The thus
obtained masked ketoaldehyde 9p is a suitable precursor for
PGE, as well as, through an elimination reaction of PGA
-via alkylation in 2). Differently from the case of 2k, dia-
stereoselectivity is modest with parent dioxolane 2p and is
unchanged when the bulky silyloxyketone 12 is used as the
trap -entry 19). Noteworthy, photochemical hydrogen
abstraction in aqueous medium using a water-soluble sensi-
tizer such as benzophenone sodium sulfonate19 markedly
improves the diastereoselectivity in the synthesis of 9p
-from 38 to 72% d.e., see Section 5) probably due to the
establishment of hydrogen bonds. This is promising in view
of the fact that related masked aldehydes have been already
employed in the synthesis of both chiral carbocyclic nucleo-
sides20a or brefeldin.20b Furthermore, the good chemical
yield in the formation of 9p/9p0 -or 9k/9k0) and the easy
conversion of the mixture into compound 11p -11k, see
Scheme 4) enhances the versatility of these products.
The ef®ciency of the key trapping step depends primarily on
the structure of the enone. With open chain enones yields
are low, particularly with the hexyldioxolanyl radical from
2n. On the other hand, satisfactory results are obtained with
®ve- and six- -butnotseven-) membered enones whit
isolated yields in the range 65±78%. The rigid structure
of these compounds make them better radical traps for
both electronic and steric reasons and causes a more favor-
able competition with the dioxolanyl radical rearrangement.
No alkylation takes place with 2-phenyl-1,3-dioxolane -2o).
In this case a strongly stabilized radical -2o is both a tertiary
and a benzylic radical, see Scheme 3) is formed and trapping
by 1 is slow. As one may expect with such persistent
radicals, termination by coupling predominates and yields
product 6 -from heterocoupling with the persistent ketyl
radical, path a) and 7 -homocoupling, path b). This is
accompanied by oxidation to hydroxyethyl esters 4o, a
process which completely supersedes rearrangement to
ethyl benzoate 5o -of which only traces are formed), an
indication of the high stabilization of radical 2o.10 A little
amountof hydroxy esetr is also formed from 2n. Notice
however that under thermal conditions benzoate esters
have been previously reported to be formed in high yield
from 2-phenyl-1,3-diox-ol)ane derivatives,13 evidencing the
temperature dependence of the fate of the radical.
4. Conclusions
Hydrogen abstraction is usually not regarded as a viable
method for the generation of alkyl radicals and their use
in the nucleophilic alkylation of enones.21 Even with
1,3-dioxolanes, when stereoselective factors greatly facili-
tate hydrogen transfer, the thermal process requires a
relatively high temperature and under such conditions rear-
rangement of the radical makes trapping by electrophilic
alkenes ineffective. Under the mild conditions of photo-
chemical initiation this limitation is overcome and the
synthesis of useful intermediates is practicable, at least
with cyclic enones.
The overall comparison -both this work and literature)
between photochemical and thermal generation of 2-alkyl-
1,3-dioxolanyl radicals makes it apparent that the mild
conditions of the former method minimize competitive
reactions and allow more ef®cient trapping by electrophilic
alkenes, except when phenyl substitution makes addition
too slow.
5. Experimental
5.1. General
NMR spectra were recorded on a 300 MHz spectrometer.
The assignments were made on the basis of H and 13C
1
3.1. Synthetic utility of the method
NMR; chemical shifts are reported in ppm down®eld from
TMS. IR spectra were in accordance for the structure with
all the new compounds and are reported in selected cases.
2-Methyl-1,3-dioxolane, 2-cyclohexen-1-one and 2-cyclo-
penten-1-one were commercial samples and were used
without puri®cation. 2-Ethyl-1,3-dioxolane,22 2--2-methyl-
propyl)-1,3-dioxolane, 2-phenyl-1,3-dioxolane and 2-hexyl-
1,3-dioxolane were synthesized from the corresponding
aldehydes -see later). 4-Hydroxy-cyclopentenone was
obtained from furfuryl alcohol.23 The photochemical reac-
tions were performed in quartz tubes by using nitrogen-
purged solution and a multilamp reactor ®tted with six
15 W phosphor-coated lamps -maximum of emission
366 nm) for the irradiation.
1,4-Diketones14 and their monoprotected derivatives are
highly versatile intermediates,15a for which a mild synthetic
entry is a desirable alternative to available methods. In par-
ticular 1,4-diketones corresponding to the dioxolanes
prepared in the present work have been employed in the
pinacolization process for the stereoselective synthesis of
monocyclic cis-cyclobutane-1,2-diols,15b as a source for
chiral diols15c,d and as intermediates for the synthesis of
molecules of biological interest.16 Furthermore, these 1,4-di-
ketones could easily transformed into cyclopentenone
derivatives used in the synthesis of antibiotics -type A
streptogramins),17a unstable cyclopentenoid antibiotic
-methylenomicyn B)17b or compounds with antifungal
activity -e.g. pinguisanes).17c
5.2. Synthesis of dioxolanes 2, general procedure
The photoinduced alkylation of 4-hydroxycyclopenten-2-
one -8) was tested in view of the possible application of
the process to prostaglandins synthesis. The yield of alkyl-
ation is high with both dioxolanes 2p and 2k and in the latter
case a marked preference for the desired trans stereo-
A solution of the suitable aldehyde, ethylene glycol and
PTSA in benzene was re¯uxed with a water separator
until the total consumption of the starting aldehyde. Usual
work-up and distillation yielded the ®nal dioxolanes.24

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R. Mosca et al. / Tetrahedron 57 '2001) 10319±10328
Compound 2m: 2--2-methylpropyl)-1,3-dioxolane -80%
3ak was formed in 49% yield -GC/MS) and was accom-
panied by a large amount-about0.3 M) of hydroxyester 4a.
1
yield) H -CDCl3) d 1.0 -d, 6H, Jˆ7 Hz), 1.5 -dd, 2H,
Jˆ5 and 7 Hz), 1.8 -m, 1H), 3.8 -m, 2H), 3.95 -m, 2H),
1
4.85 -t, 1H, Jˆ5 Hz).
Compound 3ak: H -CDCl3) d 1.3 -s, 3H), 2.0 -t, 2H, Jˆ
7 Hz), 2.15 -s, 3H), 2.5 -t, 2H, Jˆ7 Hz), 3.95 -m, 4H).27 IR
-neat) n/cm21 1717, 1052. Anal. Calcd for C8H14O3: C,
60.74; H, 8.92. Found: C, 60.70; H, 8.97.
Compound 2n: 2-hexyl-1,3-dioxolane -82% yield).25a
Compound 2o: 2-phenyl-1,3-dioxolane -67% yield).25b
Compound 4a: MS -m/z) 103 -M±1, 2), 88 -82), 73 -100), 72
-93).
5.3. Synthesis of 4--tert-butyldiphenyl-silyloxy)-cyclo-
pent-2-enone -12)
5.7.2. 4--2-Ethyl-1,3-dioxolan-2-yl)-butan-2-one -3al).
From 250 mL -3 mmol, 0.05 M) of 1a, 220 mg -1.2 mmol,
0.02 M) of benzophenone, 7 mL -60 mmol, 1 M) of 2-ethyl-
1,3-dioxolane -2l) in 60 mL of acetonitrile. After distillation
of the resulting residue, the title compound -3al, 120 mg,
28%) was isolated as a colorless liquid.
A solution of 8 -295 mg, 3 mmol), DMAP -735 mg,
6 mmol), t-BuPh2SiCl -935 mL, 3.6 mmol) in DMF
-3.8 mL) was stirred for 2 h and then poured in water and
extracted with Et2O -3 times). Crude silyl ether 12 was
puri®ed on silica gel -cyclohexane/ethyl acetate 6/4) and
isolated as an oil in an almost quantitative yield.25c
Compound 3al: 1H -CDCl3) d 0.95 -t, 3H, Jˆ7 Hz), 1.6 -q,
2H, Jˆ7 Hz), 1.95 -t, 2H, Jˆ7 Hz), 2.1 -s, 3H), 2.5 -t, 2H,
Jˆ7 Hz), 3.9 -s, 4H). 13C -CDCl3) d 8.0 -CH3), 29.7 -CH3),
30.0 -CH2), 30.3 -CH2), 38.0 -CH2), 64.7 -CH2), 111.2,
208.6 -CO). IR -neat) n/cm21 1720, 1049. Anal. Calcd for
C9H16O3: C, 62.77; H, 9.36. Found: C, 62.70; H, 9.30.
5.4. Alkylation of ketones 1 by thermal radical chain
method
AIBN as radical initiator. A solution of 1a -37 mL,
0.45 mmol, 0.05 M), 2k -810 mL, 6 mmol, 1 M), AIBN
-30 mg, 0.18 mmol, 0.02 M) in 9 mL of MeCN was heated
at40±45 8C for 1 h and then re¯uxed for 10 min. GC analy-
sis showed no formation of compound 3ak.
5.7.3. 4-[2-2-Methylpropyl)-1,3-dioxolan-2-yl)]-butan-2-
one -3am). From 210 mL -2.5 mmol, 0.05 M) of 1a,
180 mg -1 mmol, 0.02 M) of benzophenone, 6.8 mL -50
mmol, 1 M) of 2--2-methylpropyl)-1,3-dioxolane -2m) in
50 mL of acetonitrile. Column cromatography -cyclohex-
ane/ethyl acetate 8/2) separation afforded 4-[2-2-methyl-
propyl)-1,3-dioxolan-2-yl)]-butan-2-one -3am, 98 mg,
32%) as a colorless liquid.
5.5. Benzoyl peroxide as initiator26
Alkylation of 1a. To a re¯uxed solution of 2k -1.4 mL,
16 mmol, 1 M) in 5 mL of MeCN a solution of 1a -64 mL,
0.8 mmol, 0.05 M) and benzoyl peroxide -145 mg,
0.6 mmol, 0.037 M) in 3 mL of MeCN was dropwise
added in 2 h under nitrogen. After 3 h of re¯uxing only a
small amount- ,3%) of 3ak was detected by GC analysis.
Compound 3am: 1H -CDCl3) d 0.95 -d, 6H, Jˆ7 Hz), 1.5 -d,
2H, Jˆ7 Hz), 1.75 -m, 1H), 1.95 -t, 2H, Jˆ7 Hz), 2.15 -s,
3H), 2.5 -t, 2H, Jˆ7 Hz), 3.9 -s, 4H). 13C -CDCl3) d 23.8
-CH3), 24.0 -CH3), 29.7 -CH), 31.0 -CH2), 38.0 -CH2), 45.3
-CH2), 64.5 -CH2), 111.0, 208.4 -CO). IR -neat) n/cm21
1716, 1054. Anal. Calcd for C11H20O3: C, 65.97; H, 10.07.
Found: C, 66.08; H, 9.98.
5.6. Alkylation of 1d
The experimentwas carried outas in the case of 1a starting
from a 0.05 M solution of 1d. After 3 h of reaction 3dk was
formed in 21% yield.
5.7.4. Attempted synthesis of 4--2-hexyl-1,3-dioxolan-2-
yl)-butan-2-one -3an). 11 mL -0.15 mmol, 0.05 M) of 1a,
11 mg -0.06 mmol, 0.02 M) of benzophenone, 0.51 mL
-3 mmol, 1 M) of 2n in 3 mL of acetonitrile were irradiated
for 15 h. GC/MS analysis showed a little consumption of 2n
-ca. 10%) with the formation of heptanoic acid 2-hydroxy-
ethyl ester -4n, ca. 5%) and heptanoic acid ethyl ester -5n,
,2%, both based on starting dioxolane 2n). A small amount
of adduct 3an -,5%, based on alkene 1a) was also formed.
5.7. Photochemical synthesis of ketones 3, general
procedure
A solution of the enone -0.05 M), 2-alkyl-1,3-dioxolane
-1 M) and benzophenone -0.02 M) in acetonitrile was
irradiated until the enone was consumed. The reaction
course was followed by TLC -cyclohexane/ethyl acetate)
and GC. Workup of the photolytes involved concentration
in vacuo and bulb to bulb distillation or chromatographic
Ê
Compound 3an: MS -m/z) 229 -12, M11), 157 -75), 143
-100), 43 -53).
separation using Millipore 60 A, 35±70 mm silica gel.
5.7.1. 4--2-Methyl-1,3-dioxolan-2-yl)-butan-2-one -3ak).
From 210 mL -2.5 mmol, 0.05 M) of 3-buten-2-one -1a),
180 mg -1 mmol, 0.02 M) of benzophenone, 4.5 mL
-45 mmol, 1 M) of 2-methyl-1,3-dioxolane -2k) in 45 mL
of acetonitrile. After distillation of the resulting residue,
4--2-methyl-[1,3]-dioxolan-2-yl)-butan-2-one -3ak, 115 mg,
28%) was isolated as a colorless liquid.
Compound 4n: MS -m/z) 175 -66, M11), 157 -67), 113
-94), 43 -100).28
Compound 5n: MS -m/z) 158 -100, M), 113 -20), 43 -21), 41
-23).28
5.7.5. 4--2-Ethyl-1,3-dioxolan-2-yl)-pentan-3-one -3bl).
From 240 mL -2.4 mmol, 0.05 M) of 1b, 175 mg
The same reaction carried out in neat 2k -3 mL). Product

R. Mosca et al. / Tetrahedron 57 '2001) 10319±10328
10325
-0.96 mmol, 0.02 M) of benzophenone, 6 mL -48 mmol,
1 M) 2l in 48 mL of acetonitrile. After distillation of the
resulting residue, the title compound -3bl, 67 mg, 21%)
was isolated as a colorless liquid.
-1d), 180 mg -1 mmol, 0.02 M) of benzophenone, 4.5 mL
-50 mmol, 1 M) of 2k in 50 mL of acetonitrile. Separation
by column chromatography -cyclohexane/ethyl acetate 8/2)
afforded
3--2-methyl-1,3-dioxolan-2-yl)-cyclohexanone
-3dk, 220 mg, 48%) as a colorless liquid.29
Compound 3bl: 1H -CDCl3) d 0.95 -t, 3H, Jˆ7 Hz), 1.05 -t,
3H, Jˆ7 Hz), 1.65 -q, 2H, Jˆ7 Hz), 1.95 -t, 2H, Jˆ7 Hz),
2.5 -m, 4H), 3.95 -s, 4H). 13C -CDCl3) d 7.8 -CH3), 8.0
-CH3), 30.0 -CH2), 30.3 -CH2), 35.7 -CH2), 36.6 -CH2),
64.9 -2 CH2), 111.2, 211.1 -CO). IR -neat) n/cm21 1717,
1050. Anal. Calcd for C10H18O3: C, 64.49; H, 9.74. Found:
C, 64.40; H, 9.66.
1
Compound 3dk: H -CDCl3) d 1.25 -s, 3H), 1.5±1.75 -m,
2H), 1.95±2.2 -m, 3H), 2.2±2.4 -m, 3H), 2.5 -m, 1H), 3.95
-m, 4H). 13C -CDCl3) d 21.5 -CH3), 24.6 -CH2), 25.6 -CH2),
41.1 -CH2), 42.4 -CH2), 46.8 -CH), 64.6 -CH2), 64.9 -CH2),
110.3, 211.5 -CO). IR -neat) n/cm21 1710, 1224, 1146.
Anal. Calcd for C10H16O3: C, 65.19; H, 8.75. Found: C,
65.14; H, 8.77.
5.7.6.
3--2-Methyl-1,3-dioxolan-2-yl)-cyclopentanone
-3ck). From 125 mL -1.5 mmol, 0.05 M) of 2-cyclopenten-
1-one -1c), 110 mg -0.6 mmol, 0.02 M) of benzophenone,
2.7 mL -30 mmol, 1 M) of 2k in 30 mL of acetonitrile.
Separation by means of column chromatography -cyclo-
hexane/ethyl acetate 8/2) afforded 3--2-methyl-1,3-dioxo-
5.7.10. 3--2-Hexyl-1,3-dioxolan-2-yl)-cyclohexanone -3dn).
From 240 mL -2.5 mmol, 0.05 M) of 2-cyclohexen-1-one
-1d), 180 mg -1 mmol, 0.02 M) of benzophenone, 8.5 mL
-50 mmol, 1 M) of 2n in 50 mL of acetonitrile. Separation
by column chromatography -cyclohexane/ethyl acetate 9/1)
afforded the title compound -3dn, 362 mg, 57%) as a color-
less liquid.
lan-2-yl)-cyclopentanone -3ck, 200 mg, 78%) as
colorless liquid.
a
1
Compound 3ck: H -CDCl3) d 1.3 -s, 3H), 1.75±1.95 -m,
1H), 2.0±2.4 -m, 5H), 2.45±2.6 -m, 1H), 3.85±4.05 -m, 4H).
13C -CDCl3) d 22.6 -CH3), 24.0 -CH2), 38.1 -CH2), 40.0
-CH2), 45.2 -CH), 64.7 -CH2), 65.1 -CH2), 110.1, 218.7
-CO). IR -neat) n/cm21 1739, 1226, 1155. Anal. Calcd for
C9H14O3: C, 63.51; H, 8.29. Found: C, 63.53; H, 8.32.
Compound 3dn: 1H -CDCl3) d 0.8 -t, 3H, Jˆ7 Hz), 1.2±1.4
-m, 8H), 1.5±1.7 -m, 4H), 1.85±2.45 -m, 7H), 3.85 -m, 4H).
13C -CDCl3) d 14.4 -CH3), 23.0 -CH2), 23.8 -CH2), 25.1
-CH2), 25.9 -CH2), 30.0 -CH2), 32.1 -CH2), 35.5 -CH2),
41.5 -CH2), 42.7 -CH2), 45.1 -CH), 65.6 -CH2), 65.9
-CH2), 112.1, 211.6 -CO). IR -neat) n/cm21 1712, 1220,
1148. Anal. Calcd for C15H26O3: C, 70.83; H, 10.30.
Found: C, 70.85; H, 10.29.
5.7.7. 3--2-Ethyl-1,3-dioxolan-2-yl)-cyclopentanone -3cl).
From 210 mL -2.5 mmol, 0.05 M) of 2-cyclopenten-1-one
-1c), 180 mg -1 mmol, 0.02 M) of benzophenone, 6.3 mL
-50 mmol, 1 M) of 2l in 50 mL of acetonitrile. Separation
by means of column chromatography -cyclohexane/ethyl
acetate 9/1) afforded the title compound -3cl, 320 mg,
70%) as a colorless liquid.
5.7.11. Attempted alkylation with dioxolane 2o. 16.5 mL
-0.2 mmol, 0.05 M) of 1a, 14.5 mg -0.08 mmol, 0.02 M) of
benzophenone, 590 mL -4 mmol, 1 M) of 2o in 4 mL of
acetonitrile were irradiated for 4 h. GC analysis of the
®nal mixture showed a slight consumption of dioxolane
2o with the formation of four new compounds -yield less
than 2.5% each) viz. diphenyl--2-phenyl-1,3-dioxolan-2-
yl)-methanol as the main product -6), 2,20-diphenyl-
2,20bis[1,3]dioxolanylethane -7), benzoic acid 2-hydroxy-
ethyl ester -4o) and traces of ethyl benzoate -5o). These
products were identi®ed both by GC/MS analysis and
by comparison with authentic samples;30 the analysis
ascertained that product 3ao was notformed.
Compound 3cl: 1H -CDCl3) d 0.85 -t, 3H, Jˆ7 Hz), 1.65 -q,
2H, Jˆ7 Hz), 1.8 -m, 1H), 1.95±2.35 -m, 5H), 2.6 -m, 1H),
3.9 -m, 4H). 13C -CDCl3) d 8.5 -CH3), 24.2 -CH2), 29.5
-CH2), 38.6 -CH2), 40.4 -CH2), 43.2 -CH), 65.8 -CH2),
66.2 -CH2), 112.6, 219.2 -CO). IR -neat) n/cm21 1736,
1224, 1158. Anal. Calcd for C10H16O3: C, 65.19; H, 8.75.
Found: C, 65.16; H, 8.77.
5.7.8. 3--2-Hexyl-1,3-dioxolan-2-yl)-cyclopentanone -3cn).
From 210 mL -2.5 mmol, 0.05 M) of 1c, 180 mg -1 mmol,
0.02 M) of benzophenone, 8.5 mL -50 mmol, 1 M) of 2n in
50 mL of acetonitrile. Separation by means of column
chromatography -cyclohexane/ethyl acetate 9/1) afforded
the title compound -3cn, 408 mg, 68%) as a colorless liquid.
A similar reaction was carried out with ole®n 1c and again
no alkylation product was detected.
Compound 4o: MS -m/z) 167 -1, M11), 123 -44), 105 -100),
77 -81), 51 -22).
Compound 6: MS -m/z) 181 -5), 149 -100), 105 -93), 77
-63), 51 -11).
1
Compound 3cn: H -CDCl3) d 0.9 -t, 3H, Jˆ7 Hz), 1.15±
1.45 -m, 8H), 1.5±1.75 -m, 2H), 1.75±1.95 -m, 1H), 1.95±
2.45 -m, 5H), 2.55±2.7 -m, 1H), 3.8±4.1 -m, 4H). 13C
-CDCl3) d 14.0 -CH3), 22.4 -CH2), 23.7 -CH2), 23.8
-CH2), 29.5 -CH2), 31.7 -CH2), 36.3 -CH2), 38.1 -CH2),
40.0 -CH2), 43.2 -CH), 65.2 -CH2), 65.6 -CH2), 112.0,
218.8 -CO). Anal. Calcd for C14H24O3: C, 69.96; H, 10.07.
Found: C, 69.89; H, 10.11.
Compound 7: MS -m/z) 149 -100, M/2), 105 -80), 77 -52),
51 -12).
5.7.12. 3-Hydroxy-4--2-methyl-1,3-dioxolan-2-yl)-cyclo-
pentanone -9k). From 265 mg of 8 -2.7 mmol, 0.06 M),
200 mg of benzophenone -1.1 mmol, 0.024 M), 4 mL of
2k -45 mmol, 1 M) in 45 mL of acetonitrile. After the elimi-
nation of the solvent, water -45 mL) and then Et2O -30 mL)
was added to the raw photolisate. The aqueous phase was
5.7.9. 3--2-Methyl-1,3-dioxolan-2-yl)-cyclohexanone -3dk).
From 240 mL -2.5 mmol, 0.05 M) of 2-cyclohexen-1-one

10326
R. Mosca et al. / Tetrahedron 57 '2001) 10319±10328
then extracted with CH2Cl2 -30 mL£4) and the joined
extracts were dried yielding 375 mg of 3-hydroxy-4--2-
methyl-1,3-dioxolan-2-yl)-cyclopentanone -9k, 75% yield,
oil, trans isomer). The cis isomer -compound 9k0) was
detected by GC/MS technique from the photolisate mixture
-trans/cis 11/1) Stereochemistry of 9k was determined by
2D-NOESY experiment-no effectbewt een H-3 and H-4)
5.7.14. 3--1,3-Dioxolan-2-yl)-4-hydroxycyclopentanone
-9p). From 265 mg of 8 -2.7 mmol, 0.06 M), 200 mg of
benzophenone -1.1 mmol, 0.024 M) in 45 mL of neat1,3-
dioxolane 2p. After elimination of the solvent, water
-45 mL) and then Et2O -30 mL) were added to the raw
photolisate. The aqueous phase was then extracted with
CH2Cl2 -30 mL£4) and the combined extracts were dried
yielding 343 mg of 3--1,3-dioxolan-2-yl)-4-hydroxycyclo-
pentanone -mixture of isomer, 9p trans/9p0 cis 2.2/1) in
74% yield as an oil.
The ether phase was puri®ed on silica gel column -cyclo-
hexane/ethyl acetate 55/45) yielding '2S,3R,4R/2R,3S,4S)
4-hydroxy-2-'diphenylhydroxymethyl)-3-'2-methyl-1,3-di-
oxolan-2-yl)-cyclopentanone 10 -25 mg, 7.5% yield). The
all trans stereochemistry was assigned on the basis of the
virtual J coupling constants between H-2 and H-3 and
between H-3 and H-4.
The same reaction was carried out in a 1/1 water/2p mixture
of 8 in the presence of benzophenone sodium sulfonate as
the sensitizer. Dioxolane was eliminated in vacuo and
products 9p/9p0 -in a 6/1 ratio) were extracted with
CH2Cl2 from the remaining aqueous mixture -278 mg,
60% yield).
Compound 9k: 1H -CD3COCD3) d 1.35 -s, 3H), 2.1 -m, 1H),
2.15 -m, 1H), 2.4 -m, 1H), 2.5 -m, 1H), 2.55 -m, 1H), 3.9±
4.0 -m, 4H), 4.5 -m, 1H). 13C -CD3COCD3) d 22.0 -CH3),
38.0 -CH2), 46.7 -CH2), 52.6 -CH), 64.2 -CH2), 64.7 -CH2),
69.5 -CH), 109.7, 214.4 -CO). IR -neat) n/cm21 3454, 1749,
1149, 1031. Anal. Calcd for C9H14O4: C, 58.05; H, 7.58.
Found: C, 58.09; H, 7.66. MS -m/z) 187 -1, M11), 99
-16), 87 -100), 43 -37).
Compounds 9p19p0 -obtained as
a
mixture) 1H
-CD3COCD3) d 2.0±2.6 -m, 10H), 3.8±4.0 -m, 8H), 4.45
-m, 1H, 9p), 4.6 -m, 1H, 9p0), 5.0 -d, 1H, Jˆ3 Hz, 9p), 5.1
-d, 1H, Jˆ6 Hz, 9p0). 9p: -Major isomer) 13C -CD3COCD3)
d 36.0 -CH2), 46.4 -CH2), 47.6 -CH), 64.7 -CH2), 64.9
-CH2), 69.4 -CH), 103.6 -CH), 214.5 -CO). MS -m/z) 171
-1, M21), 99 -5), 73 -100), 45 -24). 9p0: -Minor isomer) 13C
-CD3COCD3) d 36.3 -CH2), 45.2 -CH), 47.9 -CH2), 64.3
-CH2), 64.5 -CH2), 68.9 -CH), 103.9 -CH), 214.6 -CO).
MS -m/z) 171 -1, M21), 99 -5), 73 -100), 45 -24). IR
-neat) n/cm21 3438, 1740, 1129.
Compound 9k0: MS -m/z) 187 -2, M11), 99 -21), 87 -100),
43 -53).
1
Compound 10: H -CDCl3) d 1.3 -s, 3H), 2.35 -bd, 1H,
Jˆ19 Hz), 2.5 -bs, 1H), 2.7 -bdd, 1H, Jˆ7 and 19 Hz),
3.6 -bs, 1H), 3.7 -m, 1H), 3.8±4.0 -m, 3H), 4.5 -bd, 1H,
Jˆ7 Hz), 7.2±7.6 -m, 10H). 13C -CDCl3) d 22.0 -CH3),
48.4 -CH2), 56.1 -CH), 56.9 -CH), 64.4 -CH2), 64.7
-CH2), 69.4 -CH), 79.8, 109.8, 126.1 -CH), 126.3 -CH),
126.7 -CH), 126.8 -CH), 127.8 -CH), 128.1 -CH), 144.4,
146.2, 215.0 -CO). IR -neat) n/cm21 3377, 1741, 1166,
1057. Anal. Calcd for C22H24O5: C, 71.72; H, 6.57.
Found: C, 71.64; H, 6.46.
5.7.15. 4--1,3-Dioxolan-2-yl)-cyclopent-2-enone. -11p).
The reaction was carried out on the raw photolisate under
the same conditions used in the synthesis of 11k starting
from 264 mg -2.7 mmol) of 8. Final puri®cation by column
chromatography -cyclohexane/ethyl acetate 65/35) yielded
133 mg -32% yield) of the title compound 11p.
1
Compound 11p: H -CDCl3) d 2.25 -dd, 1H, Jˆ2.5 and
19 Hz, A partof an ABX sysetm), 2.4 -dd, 1H, Jˆ6.5 and
19 Hz, B partof an ABX system), 3.2 -m, 1H, X partof an
ABX system), 3.8±4.0 -m, 4H), 4.85 -d, 1H, Jˆ4.5 Hz), 6.2
-dd, 1H, Jˆ2 and 6 Hz), 7.6 -dd, 1H, Jˆ2.5 and 6 Hz). 13C
-CDCl3) d 35.6 -CH2), 45.5 -CH), 65.1 -CH2), 65.2 -CH2),
104.1 -CH), 135.8 -CH), 162.4 -CH), 208.7 -CO). IR -neat)
n/cm21 1707, 1588, 1065. Anal. Calcd for C8H10O3: C,
62.33; H, 6.54. Found: C, 62.30; H, 6.55.
5.7.13. 4--2-Methyl-1,3-dioxolan-2-yl)-cyclopent-2-enone
-11k). The synthesis described above was repeated and the
crude photolisate was dissolved in pyridine at 2108C and
then methanesulfonyl chloride was added dropwise.31 The
mixture was stirred for 1 h and allowed to reach room
temperature under stirring in 2 h. Et2O was then added
along with cold 5% HCl and the two phases poured in a
separatory funnel with the help of further Et2O. The organic
phase was separated and washed with 5% NaHCO3 and
brine. The solution obtained was dried, the solvents
evaporated and the residue puri®ed on silica gel column
-cyclohexane/ethyl acetate 6/4) affording the title com-
pound -11k, 181 mg, oil) in 40% yield -based on cyclo-
pentenone 8).
5.7.16. 3--tert-Butyldiphenylsilyloxy)-4-[1,3]dioxolan-2-
yl-cyclopentanone -13). From 900 mg of 12 -2.7 mmol,
0.06 M), benzophenone -1.05 mmol, 0.024 M) in 1,3-dioxo-
lane -45 mL). Puri®cation -silica gel column, cyclohexane/
ethyl acetate 9/1) afforded 515 mg of 3--tert-butyldiphenyl-
silyloxy)-4-[1,3]dioxolan-2-yl-cyclopentanone 13 -trans
isomer, 46% yield) and 246 mg of 3--tert-butyldiphenyl-
silyloxy)-4-[1,3]dioxolan-2-yl-cyclopentanone 130 -cis
isomer, 22% yield). The stereochemistry of both isomers
was deduced from 2D-NOESY experimenton compound
130. In this case a correlation between H-3 and H-4 was
observed and proved the cis con®guration.
Compound 11k: 1H -CDCl3) d 1.3 -s, 3H), 2.3 -dd, 1H, Jˆ3
and 19 Hz, A partof an ABX sysetm), 2.4 -dd, 1H, Jˆ6.5
and 19 Hz, B partof an ABX system), 3.25 -m, 1H, X partof
an ABX system), 3.85±4.05 -m, 4H), 6.25 -dd, 1H, Jˆ2 and
6 Hz), 7.6 -dd, 1H, Jˆ2.5 and 6 Hz). 13C -CDCl3) d 22.2
-CH3), 36.9 -CH2), 50.2 -CH), 65.0 -CH2), 65.1 -CH2),
109.7, 135.6 -CH), 163.3 -CH), 209.2 -CO). IR -neat)
n/cm21 1708, 1587, 1055. Anal. Calcd for C9H12O3: C,
64.27; H, 7.19. Found: C, 64.22; H, 7.24.
Compound 13: 1H -CD3COCD3) d 1.1 -s, 9H), 2.05±2.2 -m,
2H), 2.35±2.5 -m, 2H), 2.7 -m, 1H), 3.7±3.85 -m, 4H), 4.6
-m, 1H), 4.75 -d, 1H, Jˆ3 Hz), 7.5 -m, 6H), 7.75 -m, 4H).

R. Mosca et al. / Tetrahedron 57 '2001) 10319±10328
10327
13C -CD3COCD3) d 18.7, 26.3 -CH3), 35.5 -CH2), 46.8
-CH2), 48.0 -CH), 64.7 -CH2), 64.9 -CH2), 72.1 -CH),
103.0 -CH), 128.0 -CH), 129.8 -CH), 133.4, 133.5, 135.6
-CH), 214.2 -CO). IR -neat) n/cm21 3069, 1744, 1111,
1051. Anal. Calcd for C24H30O4Si: C, 70.21; H, 7.36.
Found: C, 70.13; H, 7.40.
Yunker, M. B.; Tam, S. Y.-K.; Anderson, R. C. Tetrahedron
Lett. 1975, 297. -c) Rosenthal, I.; Elad, D. J. Org. Chem. 1968,
33, 805.
9. -a) Malatesta, V.; Ingold, K. U. J. Am. Chem. Soc. 1981, 103,
609. -b) The occurrence of path e is supported by the fact that
the photochemical alkylation of 1,3-dioxin-4-ones by 1,3-
dioxolanyl radical has been reported to occur in the absence
of the sensitiser, although a long irradiation time was required
-12 days, see ref. 9c). -c) Graalfs, H.; Froehlich, R.; Wolff, C.;
Mattay, J. Eur. J. Org. Chem. 1999, 1057.
Compound 130: 1H -CD3COCD3) d 1.1 -s, 9H), 2.1 -m, 2H),
2.15±2.4 -m, 2H), 2.5 -m, 1H), 3.8±4.0 -m, 4H), 4.8 -m,
1H), 5.3 -d, 1H, Jˆ5.5 Hz), 7.5 -m, 6H), 7.75 -m, 4H). 13C
-CD3COCD3) d 19.4, 26.8 -CH3), 37.4 -CH2), 46.0 -CH),
47.6 -CH2), 64.9 -CH2), 65.2 -CH2), 72.4 -CH), 104.2 -CH),
128.1 -CH), 130.3 -CH), 133.5, 134.3, 136.1 -CH), 136.2
-CH), 214.0 -CO). IR -neat) n/cm21 3069, 1744, 1111,
1041. Anal. Calcd for C24H30O4Si: C, 70.21; H, 7.36.
Found: C, 70.11; H, 7.44.
10. The reduction of 1,3-dioxolan-2-yl radicals by ground state
benzophenone is markedly endoergonic, as apparentby hte
comparison of the oxidation potential of these radicals -see
below and Ref. 11) and the reduction potential of the sensitiser
-21.68 vs SCE, Ref. 12). However, when the radical is persis-
tent and neither rearranges nor adds to alkenes easily as in the
case of the phenyl derivative, electron transfer becomes
signi®cant.
Acknowledgements
R. M. thanks Prochimica for a fellowship. We are greatly
indebted to Millipore for the grant of silica gel. Partial
supportof htis work by Murst-COFIN Program) Rome
is gratefully acknowledged. We thank Dr P. P. Rossi
-Prochimica) for his interest in this work.
11. Fontana, F.; Kolt, R. J.; Huang, Y.; Wayner, D. D. M. J. Org.
Chem. 1994, 59, 4671.
12. Photoinduced Electron Transfer; Fox, M. A., Chanon, M.,
Eds.; Elsevier: Amsterdam, 1988; p 476, Part A.
References
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and p 3663.
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A. J. Org. Chem. 1999, 64, 5024.
14. A variety of methods has been reported for the synthesis of
1,4-diketones, a selection being as follows. From ketones via
nitroaldol reaction, see Rosini, G.; Ballini, R. Synthesis 1988,
833. The palladium-catalyzed oxidation of g-ketoalkenes, see
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2001, 101, 53. -b) Carini, S.; Cere, V.; Peri, F.; Pollicino, S.
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cited herein. -b) Gronowitz, S. The Chemistryof Heterocyclic
Compounds; Gronowitz, S., Ed.; Wiley: New York, 1985;
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15. -a) Monoprotected 1,4-diketones were used recently in the
synthesis of zaragozic acid, see Hegde, S. G.; Myles, D. C.
Tetrahedron Lett. 1997, 38, 4329. -b) As well as of medium-
sized cyclic enol ethers or dienol ethers, see Mori, T.;
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5. -a) Ryabinina, T. A.; Kruglov, D. E.; Pastushenko, E. V.;
Terent'ev, A. B. Russ. J. Org. Chem. 1992, 28, 602.
-b) Batyrbaev, N. A.; Zorin, V. V.; Zlot-Skii, S. S.; Rakhman-
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6. Some exceptions were recently described, viz an oxidative
dioxolanyl radical attack onto a,b-unsatured esters see:
Hirano, K.; Iwahama, T.; Sakaguchi, S.; Ishii, Y. Chem.
Commun. 2000, 2457. Intramolecular dioxolanyl radical cycli-
zation onto alkenes in the presence of thiols see: Dang, H.-S.;
Roberts, B. P. Tetrahedron Lett. 1999, 40, 8929.
16. 1,4-Diketones arising from the open chain dioxolanes
obtained in this work were used in the synthesis of radio-
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