Peroxycarbenium-mediated C-C bond formation: Applications to the synthesis of hydroperoxides and peroxides

Article abstract of DOI:10.1021/jo991714z

The Lewis acid-mediated reaction of alkene nucleophiles with peroxyacetals provides an effective route for the synthesis of homologated peroxides and hydroperoxides. In the presence of Lewis acids such as TiCl₄, SnCl₄, and trimethylsilyl triflate, peroxyacetals and peroxyketals undergo reaction with allyltrimethylsilane, silyl enol ethers, and silyl ketene acetals to afford homoallyl peroxides, 3-peroxyketones, and 3-peroxyalkanoates, respectively. Reactions of peroxyacetals are Lewis acid dependent; TiCl₄ promotes formation of ethers while SnCl₄ and trimethylsilyl triflate promote formation of peroxides. Lewis acid-promoted reactions of silylated hydroperoxyacetals furnish silylated hydroperoxides, which can be deprotected to homologated hydroperoxides. Hydroperoxyketals undergo Lewis acid-mediated allylation to furnish 1,2-dioxolanes via attack of hydroperoxide on the intermediate carbocation. Lewis acid-mediated cyclization of unsaturated peroxyacetals furnishes 1,2-dioxanes, 1,2-dioxepanes, and 1,2-dioxacanes through 6-endo/exo, 7-endo/endo, and 8-endo/endo pathways. The corresponding reactions involving 6-endo/endo and 5-endo/exo pathways were unsuccessful.

Full text of DOI:10.1021/jo991714z

VOLUME 65, NUMBER 25
DECEMBER 15, 2000
© Copyright 2000 by the American Chemical Society
Articles
P er oxyca r ben iu m -Med ia ted C-C Bon d F or m a tion : Ap p lica tion s to
th e Syn th esis of Hyd r op er oxid es a n d P er oxid es
Patrick H. Dussault,* In Quen Lee, Hyung-J ae Lee, Richard J . Lee, Q. J ason Niu,
J effrey A. Schultz, and Umesh R. Zope
Department of Chemistry, University of NebraskasLincoln, Lincoln, Nebraska 68588-0304
Received November 2, 1999 (Revised Manuscript Received September 22, 2000)
The Lewis acid-mediated reaction of alkene nucleophiles with peroxyacetals provides an effective
route for the synthesis of homologated peroxides and hydroperoxides. In the presence of Lewis
acids such as TiCl4, SnCl4, and trimethylsilyl triflate, peroxyacetals and peroxyketals undergo
reaction with allyltrimethylsilane, silyl enol ethers, and silyl ketene acetals to afford homoallyl
peroxides, 3-peroxyketones, and 3-peroxyalkanoates, respectively. Reactions of peroxyacetals are
Lewis acid dependent; TiCl4 promotes formation of ethers while SnCl4 and trimethylsilyl triflate
promote formation of peroxides. Lewis acid-promoted reactions of silylated hydroperoxyacetals
furnish silylated hydroperoxides, which can be deprotected to homologated hydroperoxides.
Hydroperoxyketals undergo Lewis acid-mediated allylation to furnish 1,2-dioxolanes via attack of
hydroperoxide on the intermediate carbocation. Lewis acid-mediated cyclization of unsaturated
peroxyacetals furnishes 1,2-dioxanes, 1,2-dioxepanes, and 1,2-dioxacanes through 6-endo/exo, 7-endo/
endo, and 8-endo/endo pathways. The corresponding reactions involving 6-endo/endo and 5-endo/
exo pathways were unsuccessful.
The growing number of bioactive peroxide natural
products has led to increased awareness of the need for
improved synthetic methodology.1-3 We recently reported
a new strategy for peroxide synthesis based upon Lewis
acid-mediated reactions of monoperoxyacetals with elec-
tron-rich alkenes, a process involving intermediate per-
oxycarbenium ions (Scheme 1).4 The corresponding chem-
istry of nonperoxidic acetals is an important method for
synthesis of ethers, and we were curious whether reac-
tions of peroxyacetals might offer a similarly versatile
approach to functionalized peroxides.5-9 This paper dem-
onstrates the scope of the peroxycarbenium ion chemistry
for construction of acyclic and cyclic ethers, peroxides,
and hydroperoxides and illustrates the influence of Lewis
acid, substrate, and nucleophile on reaction selectivity
(Scheme 1).
Su bstr a tes. The majority of monoperoxyacetal sub-
strates were prepared through ozonolysis of alkenes or
enol ethers, followed by alkylation or silylation of the
(1) Dussault, P. H. In Active Oxygen in Chemistry; Foote, C. S.,
Valentine, J . S., Greenberg, A., Liebman, J . F., Eds.; Blackie A & P:
London, 1995; p 141.
(2) Porter, N. A. In Organic Peroxides; Ando, W., Ed.; J ohn Wiley
& Sons: Chichester, 1992; p 101.
(3) Sheldon, R. A. In Chemistry of Peroxides; Patai, S., Ed.; J ohn
Wiley & Sons: Chichester, 1983; Vol. 1, p 161.
(4) Dussault, P. H.; Lee, I. Q. J . Am. Chem. Soc. 1993, 115, 6458.
(5) Mukaiyama, T.; Mukaiyama, M. Synthesis 1987, 1043.
(6) Majetich, G. In Organic Synthesis: Theory and Applications;
Hudlicky, T., Ed.; J AI: Greenwich, CT, 1989; Vol. 1, p 173.
(7) Gennari, C. In Comprehensive Organic Synthesis; Trost, B. M.,
Fleming, I., Eds.; 1988; Vol. 2, p 629.
(8) Fleming, I.; Dunogues, J .; Smithers, R. Org. React. 1989, 37, 57.
(9) Chan, T.-H. In Comprehensive Organic Synthesis; Trost B. M.,
Fleming, I., Eds.; 1988; Vol. 2, p 595.
10.1021/jo991714z CCC: $19.00 © 2000 American Chemical Society
Published on Web 11/10/2000

8408 J . Org. Chem., Vol. 65, No. 25, 2000
Dussault et al.
Ta ble 2. Allyla tion of Mon op er oxyk eta ls
Sch em e 1. P er oxyca r ben iu m Ion Discon n ection
Ta ble 1. Su bstr a te P r ep a r a tion
hydride source is an important method for synthesis of
ethers.18 The stability of the peroxyketals toward hydride-
transfer agents (ketal 1b, for example, is unaffected by
brief treatment with Et3SiH or n-Bu3SnH and related
ketals are known to survive reduction of aldehydes by
aluminum hydrides)19,20 led us to investigate Lewis acid-
mediated reduction as an approach to secondary perox-
ides. However, attempted reduction under conditions
similar to those employed for nonperoxidic acetals led
only to decomposition or disproportionation (eq 1).21,22
Rea ction s of P er oxya ceta ls: Syn th esis of Sec-
on d a r y P er oxid es a n d Hyd r op er oxid es. The allyla-
tion of peroxyacetals, investigated as an approach to
secondary peroxides and hydroperoxides, displayed a
strong dependence on Lewis acid (Table 3). For example,
TiCl4-mediated allylation of 6c occurred at -78 °C to
afford homoallyl ether 16. SnCl4-mediated reaction did
not occur at -78 °C; however, warming to 0 °C resulted
in highly selective formation of peroxide 17. Addition at
0 °C resulted in a mixture of ether and peroxide. Other
promoters were less effective. A similar Lewis acid
dependence was observed for acetals 6d and 8d . The
tendency of TiCl4 to promote formation of ether (loss of
peroxide) could be reversed by the use of methoxyethoxy
acetals 7d and 9d .23-25 The use of allyltributyltin gave
lower yields, implying a competition between allylation
and transmetalation to a less nucleophilic allylstan-
nane.26
resulting hydroperoxyacetals (Table 1).10-13 Substrates
4b, 11e, and 12i were obtained from acid-catalyzed
acetalization of hydroperoxides.14,15
Allyla tion of Mon op er oxyk eta ls. Allylation of mono-
peroxyketals was initially investigated under conditions
analogous to those reported for nonperoxidic acetals.5,16
Addition of TiCl4 to a solution of allyltrimethylsilane and
peroxyketal 1b led to the rapid formation of homoallyl
peroxide 13 (Table 2); premixing the peroxyketal and
TiCl4 resulted in a slight improvement. Moderate to good
yields were also obtained in the presence of SnCl4 and
BCl3. Use of BF3‚OEt2 resulted in formation of a bisper-
oxyketal dimer (14).17 The corresponding SnCl4- or TiCl4-
mediated allylation of cyclohexanone monoperoxyketal
4b provided good yields of peroxide 15.
Deprotection of the allylated silyl peroxide (19) pro-
vided hydroperoxide 22,12,27 with the overall four-step
procedure (ozonolysis, silylation, allylation, and depro-
(18) Kotsuki, H. Synlett 1992, 97.
(19) Lee, I. Q. Ph.D. Thesis, University of Nebraska, 1993.
(20) Dussault, P.; Sahli, A.; Westermeyer, T. J . Org. Chem. 1993,
58, 5469.
(21) Lewis, M. D.; Cha, J . K.; Kishi, Y. J . Am. Chem. Soc. 1982,
104, 4976.
Attem p ted Red u ction of P er oxyk eta ls. The reduc-
tion of acetals in the presence of Lewis acids and a mild
(22) Tsunoda, T.; Suzuki, M.; Noyori, R. Tetrahedron Lett. 1979, 48,
4679.
(23) Nishiyama, H.; Itoh, K. J . Org. Chem. 1982, 47, 2496.
(24) Nikolic, N. A.; Gonda, E.; Longford, C. P. D.; Lane, N. T.;
Thompson, D. W. J . Org. Chem. 1989, 54, 2748.
(25) Castan˜ada, A.; Kucera, D. J .; Overman, L. E. J . Org. Chem.
1989, 54, 5695.
(26) Keck, G. E.; Castellino, S.; Andrus, M. B. In Selectivities in
Lewis Acid Promoted Reactions; Schinzer, D., Ed.; Kluwer: Dordrecht,
1989; Vol. 289, p 73.
(27) Adam, W.; Catalani, L. H.; Saha-Mo¨ller, C. R. Synthesis 1989,
121.
(10) Dussault, P.; Sahli, A. J . Org. Chem. 1992, 57, 1009.
(11) Dussault, P. H.; Zope, U. R.; Westermeyer, T. A. J . Org. Chem.
1994, 59, 8267.
(12) Clark, G. R.; Nikaido, M. M.; Fair, C. K.; Lin, J . J . Org. Chem.
1985, 50, 1994.
(13) Lohaus, G. Liebigs Ann. Chem. 1953, 583, 6.
(14) Rigaudy, J .; Izoret, G. C. R. Hebd. Seances Acad. Sci. 1953,
236, 2086.
(15) Dussault, P.; Sahli, A. Tetrahedron Lett. 1990, 31, 5117.
(16) Hosomi, A.; Endo, M.; Sakurai, H. Chem. Lett. 1976, 9410.
(17) Rieche, A.; Bischoff, C.; Dietrich, P. Chem. Ber. 1961, 94, 2932.

Peroxycarbenium-Mediated C-C Bond Formation
J . Org. Chem., Vol. 65, No. 25, 2000 8409
Ta ble 3. Allyla tion of P er oxya ceta ls
Ta ble 4. Cr otyla tion of P er oxya ceta ls
Ta ble 5. Rea ction of P er oxya ceta ls w ith a n En ol Eth er
Ta ble 6. Syn th esis of 3-P er oxy-2-m eth yla lk a n oa tes
tection) offering a new protocol for conversion of an
alkene into a homologated hydroperoxide (eq 2).
Reaction of peroxyacetal 6d with an 85:15 E/Z-mixture
of crotyltrimethylsilane in the presence of stoichometric
SnCl4 or catalytic TMSOTf produced methallyl peroxide
23 as a 2:1 syn/anti mixture (Table 4); similar results
were observed for the TiCl4-mediated reactions of meth-
oxyethoxy peroxyacetal 7d . Improved syn diastereose-
lection was observed with benzylic peroxyacetal 8d ,
paralleling results reported for nonperoxidic acetals.28
The magnitude of the diastereoselection was determined
by 1H NMR, while configurational assignments are based
upon conversion of 23 and 24 to alcohols 26 and 28.29
Syn th esis of 3-P er oxyk eton es. Reaction of peroxy-
ketal 1b with silyl enol ethers cleanly furnished 3-per-
oxyketones (eq 3).
3-peroxyalkanoates (Table 6). In contrast, reaction with
SKAs derived from ethyl propionate furnished 3-peroxy-
2-methylalkanoates (33); a similar mixture of syn and
anti diastereomers was obtained regardless of whether
the (E)- or (Z)-SKA was used. Reaction of the propionate
SKAs with the benzylic peroxyacetals 8d and 9d pro-
ceeded in higher yield but without diastereoselection.
The stereochemistry of syn- and anti-33 was assigned
following deprotection and reduction to furnish a 70:30
mixture of anti- and syn-3-hydroxy-2-methylalkanoates
35 (eq 4).
The corresponding reactions of peroxyacetals 6d , 7d ,
and 8d furnished peroxyketones 31 and 32 (Table 5), with
the best results obtained in the presence of catalytic
TMSOTf.
Syn th esis of 3-P er oxyester s. Reactions of aliphatic
peroxyacetal 6d with trimethylsilyl ketene acetals (SKAs)
of ethyl acetate or ethyl thioacetate failed to produce
Deprotection with n-Bu4NF proceeded in good yield but
resulted in formation of 34 as a 50:50 mixture of syn and
anti diastereomers, based upon conversion to syn- and
(28) Hosomi, A.; Ando, M.; Sakurai, H. Chem. Lett. 1986, 365.
(29) Hoffmann, R. W.; Zeib, H.-J . J . Org. Chem. 1981, 46, 1309.

8410 J . Org. Chem., Vol. 65, No. 25, 2000
Dussault et al.
Ta ble 8. Syn th esis of 1,2-Dioxola n es
Ta ble 7. Allyla tion of a 1,2-Dioxin e
anti-36.30,31 The ability to achieve epimerization without
decomposition, a surprising outcome given the interme-
diacy of â-peroxyenolates in nucleophilic epoxidations,32,33
offers a potential means of selectively obtaining either
syn- or anti-peroxypropionates.
Allyla tion of Cyclic P er oxya ceta ls: Syn th esis of
1,2-Dioxin es. Allylation of cyclic peroxyacetals was
investigated as a potential approach to the 1,2-dioxane
core of a number of natural products.34,35 Allylation of
alkoxydioxine 37 in the presence of either TiCl4 or SnCl4
produced moderate yields of allylated dioxine (Table 7).
The product was invariably isolated as a 3:2 cis/trans
mixture, regardless of the stereochemistry of 37. Dia-
stereomers were identified by comparison of the H3-H4
coupling constants against reported values for simple
endoperoxides.36 Dioxine 37 failed to react with several
silyl ketene acetals, even though the presence of a
reactive intermediate could be verified by trapping with
allytrimethylsilane. Attempted allylation of a saturated
analog37 led only to ring-opened products.
Disp la cem en t of Hyd r op er oxya ceta ls: Syn th esis
of Dioxola n es. The 1,2-dioxolane moiety forms the core
of prostaglandins, oxidized lipids, and the plakinic acid
family of marine natural products.34,35,38 An otherwise
attractive approach to this substructure based upon 1,3-
dipolar addition39-42 is limited by the compatibility of
alkenes with ozonolysis, the most common method for
the generation of carbonyl oxides.43 Protonated and
metalated carbonyl oxides capable of 1,3-dipolar addition
have been generated via acid-catalyzed decomposition of
ozonides (1,2,4-trioxolanes).39,44 We were interested in
employing Lewis acid-mediated ionization of hydroper-
oxyacetals to furnish reactive hydroperoxycarbenium ions
which would react with alkenes to form 1,2-dioxolanes
(Table 8).45,46 In particular, we were curious about
selective activation of an alkoxide in the presence of a
free hydroperoxide and in the relative rate of the desired
transformation versus acid-catalyzed disproportion-
ation.47
As illustrated in Table 8, SnCl4-promoted reactions of
hydroperoxyketals 1a , 4a , and 5a furnished trimethyl-
silylmethyl-1,2-dioxolanes in moderate to good yield.
However, reaction of hydroperoxyacetals 6a or 7a fur-
nished little or no dioxolane. A more functionalized
hydroperoxyketal (10a ), prepared as a model for the
plakinic acid class of 1,2-dioxolane natural products,
furnished mostly ketone.48,49 TiCl4-mediated reactions
tended to favor alternate pathways. Hydroperoxyketal
2a , for example, produced allylated peroxide, implying
that the presence of a bidentate leaving group is able to
influence the product distribution. TiCl4-mediated reac-
tions of acetals 6a and 7a furnished allyl ethers via loss
of the hydroperoxide, while cyclohexane hydroperoxy-
acetal 4a reacted to form a bisallylated peroxide, pre-
sumably via 2-fold allylation of an intermediate 1,1′-
bisalkoxyperoxide. The allylated products derived from
4a and 5a were each isolated as a single diastereomer
(13C), suggesting predominant equatorial attack on the
hydroperoxycarbenium or peroxycarbenium intermedi-
ate.48 All examples reported are based upon rapid addi-
tion of Lewis acid to a chilled mixture of alkoxyhydro-
peroxide and allylsilane; slow addition of Lewis acid or
premixing of the hydroperoxide and Lewis acid gave
much lower yields. Attempts to employ allyltributylstan-
nane, enol ethers, or enamines as nucleophiles were
unsuccessful.
(30) Taniguchi, M.; Fujii, H.; Oshima, K.; Utimoto, K. Tetrahedron
1993, 49, 11169.
(31) Davies, S. G.; Edwards, A. J .; Evans, G. B.; Mortlock, A. A.
Tetrahedron 1994, 50, 6621.
(32) Paquette, L. A.; Carr, R. V. C.; Bellamy, F. J . Am. Chem. Soc.
1978, 100, 6764.
(33) Yang, N. C.; Finnegan, R. A. J . Am. Chem. Soc. 1958, 80, 5845.
(34) Casteel, D. A. Nat. Prod. Rep. 1999, 16, 55.
In tr a m olecu la r Ad d ition s. Intramolecular additions
to activated carbonyl and acetal groups have been widely
used for construction of carbocycles and cyclic ethers.50,51
We were interested in corresponding additions to per-
oxycarbenium ions as a new approach to cyclic peroxides.
In particular, we hoped the entropic advantages of an
intramolecular reaction might permit the use of simple
alkenes as nucleophiles.52 Intramolecular attack of al-
kenes onto peroxycarbenium ions, much like reactions
of corresponding oxycarbenium ions, can be classified by
(35) Casteel, D. A. Nat. Prod. Rep. 1992, 289.
(36) O’Shea, K. E.; Foote, C. S. J . Am. Chem. Soc. 1988, 110, 7167.
(37) Dussault, P. H.; Kreifels, S.; Lee, I. Q. Synth. Commun. 1995,
25, 2613.
(38) Yamamoto, S. In Comprehensive Natural Products Synthesis;
Sankawa, V., Ed.; Pergamon: New York, 1999; Vol. 1.
(39) McCullough, K. J .; Nojima, M. In Organic Peroxides; Ando, W.,
Ed.; J ohn Wiley & Sons: Chichester, 1992; p 661.
(40) Kuczkowski, R. L. In Advances in Oxygenated Processes; Baum-
stark, A. L., Ed.; J AI: Greenwich, CT, 1991; Vol. 3, p 1.
(41) Graziano, M. L.; Iesce, M. R.; Cermola, F.; Giordano, F.;
Scaparti, R. J . Chem. Soc., Chem. Commun. 1989, 1608.
(42) Casey, M.; Culshaw, A. J . Synlettt 1992, 214.
(43) Bunnelle, W. H. Chem. Rev. 1991, 91, 335.
(44) Miura, M.; Nojima, M. J . Am. Chem. Soc. 1980, 102, 288.
(45) Dussault, P. H.; Zope, U. R. Tetrahedron Lett. 1995, 36, 3655.
(46) Ushigoe, Y.; Kawamura, S.-I.; Teshima, K.; Nojima, M.; Mc-
Cullough, K. J . Tetrahedron Lett. 1996, 37, 2093.
(47) Miura, M.; Nojima, M. J . Chem. Soc., Chem. Commun. 1979,
467.
(48) Noyori, R.; Murata, S.; Suzuki, M. Tetrahedron 1981, 37, 3899.
(49) Phillipson, D. W.; Rinehart, K. L., J r. J . Am. Chem. Soc. 1983,
105, 7735.
(50) Snider, B. B. In Comprehensive Organic Synthesis; Trost, B.
M., Fleming, I., Eds.; 1988; Vol. 2, p 527.
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784.

Peroxycarbenium-Mediated C-C Bond Formation
Ta ble 9. 6-En d o/Exo Cycliza tion s
J . Org. Chem., Vol. 65, No. 25, 2000 8411
Given the substantial precedent for 6-endo/endo cy-
clizations of oxycarbenium ions,23,51,54-57 our results imply
stereochemical constraints unique to unsaturated mono-
peroxycarbenium ions.
We next investigated cyclization through a 6-exo/exo
pathway (Scheme 2). Ozonolysis of methylcyclohexene in
methoxyethanol afforded an unstable hydroperoxyalde-
hyde which was directly alkylated to form peroxide 55.
Wittig olefination produced the unsaturated peroxyketal
56 which underwent cyclization to afford dioxanes bear-
ing an exocyclic chloride (57) as well as an alkene (58).
The differing diastereoselection observed in the formation
of 57 and 58 implies the presence of different reaction
pathways.
the exo or endo relationship of both the electrophilic
peroxycarbenium ion and the nucleophilic alkene to the
newly forming ring (eq 5).53
Although 5-endo-trig closures are well-precedented in
cyclizations of acetal-derived oxycarbenium ions,23,56,58
attempts to synthesize 1,2-dioxolanes through 5-endo/exo
cyclizations of monoperoxyketals were unsuccessful (Table
11). Peroxyketal 1j decomposed upon treatment with
Lewis acid, and no allylation was observed in the pres-
ence of allylsilane. Curiously, the methoxyethoxy ketal
2j reacted to form a 1,3-dioxane in the presence or
absence of allylsilane. A possible mechanism involves a
very rapid 6-endo cyclization to an unstable 1,2-dioxane
followed by Lewis-acid mediated Hock fragmentation.59
Peroxycarbenium ion cyclizations were also investi-
gated as an entry to medium ring peroxides. Cyclization
of monoperoxyacetal 1k with TiCl4 proceeded via the
expected 7-endo/endo pathway to afford a dioxepane.
(Scheme 3). However, in a result reminiscent of the
5-endo/exo attempts, peroxide 1l did not cyclize via the
expected 7-endo/exo mode, instead closing via an 8-endo/
endo pathway to furnish a 16% yield of a 1,2-dioxocane
as a 2.4:1 ratio of diastereomers. A similar outcome in
reactions of unsaturated oxycarbenium ions has been
rationalized through transannular stabilization of the
developing charge by the remote oxygen.60
The large number of natural products containing 1,2-
dioxane or 1,2-dioxine ring systems led to an initial
emphasis on six-membered ring construction.34,35
Addition of either TiCl4 or SnCl4 to a -78 °C solution
of peroxyketal 1e afforded dioxane 45 in good yield
through a 6-endo/exo pathway (Table 9). The same
product was obtained, albeit in slightly reduced yield,
from the ethoxy analogue 3e. In pleasant contrast to the
corresponding intermolecular reactions, low-temperature
cyclization was successful for less-stabilized peroxycar-
benium ions; monoperoxyacetal 6e underwent cyclization
to a 2.6:1 cis/trans mixture of dioxanes 46. A similar
cyclization of acetal 11e furnished a 5:1 cis/trans mixture
of dioxanes 47 in which the displaced methoxyl leaving
group also acts as a cation trapping agent; only a trace
of the tertiary chloride 48 was isolated. Stereochemical
assignments are based upon the J 3-4 coupling constants.
Nucleophilicity is clearly important as disubstituted
alkenes 6f and 2f failed to undergo cyclization, instead
furnishing dimers. Attempted cyclization of 2f also
produced a 3-peroxyketone (51) presumably arising from
intermolecular reaction between a peroxycarbenium ion
and the methoxypropenyl ether derived from decomposi-
tion of the peroxyketal.
We also investigated the relative rate of 6-endo/exo
cyclizations compared with intermolecular allylation
(Table 10). In each case investigated, addition of stoicho-
metric allyltrimethylsilane completely suppressed cy-
clization.
The 6-endo/endo class of cyclizations was anticipated
to open the door to a variety of 1,2-dioxane-containing
natural products. Unfortunately, the addition of Lewis
acids to unsaturated peroxyketals 1g-i and 12i resulted
only in decomposition. In the latter case, the successful
formation of a reactive intermediate was confirmed by
intermolecular trapping product with allylsilane (eq 6).
Discu ssion
The Lewis acid-mediated addition of nucleophiles to
peroxyacetals, peroxyketals, hydroperoxyketals, and si-
lylated hydroperoxyacetals provides a new and general
approach to the synthesis of acyclic and cyclic hydro-
peroxides and peroxides. The starting materials are
readily available and relatively stable. The products,
homoallyl peroxides or 3-peroxycarbonyls, are common
(54) Cockerill, G. S.; Kocienski, P. J . Chem. Soc., Chem. Commun.
1983, 705.
(55) Coppi, L.; Ricci, A.; Taddei, M. J . Org. Chem. 1988, 53, 911.
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N. Tetrahedron 1994, 50, 7115.
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1985, 50, 3925.
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Organische Peroxo-Verbindungen; Kropf, H., Ed.; George Thieme
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8412 J . Org. Chem., Vol. 65, No. 25, 2000
Dussault et al.
Ta ble 10
Sch em e 2. 6-Exo/Exo Cycliza tion a
Sch em e 4. Ava ila ble Ion iza tion Mod es
practical differences exist between the reactions described
in this paper and corresponding reactions of acetals. More
forcing reaction conditions are generally required as
compared with reactions of acetals. Once formed, the
presumed peroxycarbenium ion appear to be less reactive
toward alkenes than corresponding oxycarbenium ion.
Another difference from the chemistry of acetals is that
peroxyacetals are able to enter into three different modes
of ionization (Scheme 4). Although Hoch cleavage (O-O
heterolysis)59 was rarely observed in our studies, both
C-O and C-OO ionization can clearly occur.
a
a. Ozone, 2-methoxyethanol (43%); b. CsOH, MeI (29%); c.
isopropylidene triphenylphosphorane (37%); TiCl4, -78 °C, 5 min.
Ta ble 11. Attem p ted 5-Exo/En d o Cycliza tion s
Our results demonstrate that reaction selectivity is
influenced by nucleophile, Lewis acid, and substrate
structure. In the presence of good nucleophiles, mono-
peroxyketals invariably react via selective loss of the
alkoxide unit to form new peroxides. Depending upon the
choice of Lewis acid, peroxyacetals can furnish either
ether or peroxide products; the origin of this selectivity
will be addressed in detail in a separate paper. Finally,
in the absence of an effective nucleophile, either the
peroxyacetals or the derived peroxycarbenium ions readily
disproportionate to bisperoxyacetals.
Sch em e 3. Med iu m -Rin g Cycliza tion
In conclusion, we have demonstrated a fundamentally
new method for the synthesis of peroxides and hydro-
peroxides which provides a practical method for the
synthesis of allylated peroxides, peroxyketones, and
peroxyesters.
Exp er im en ta l Section
Caution: As in any work involving peroxides, standard
precautions (minimal scale; avoidance of heat, light, or metal
salts; use of safety shields) should be faithfully observed.63-67
2-(2-Methoxy)prop-2-yl hydroperoxide (1a ),10 (2-methoxy-
propy-2-yl)octyl peroxide (1b ),10 2-(2-methoxyethoxy)prop-2-
yl hydroperoxide (2a ),11 (2-methoxyethoxy)prop-2-yloctyl per-
subunits in many peroxide-containing natural products.
Many aspects of the reaction (stereoselection, reactivity
vs substrate structure) support the intermediacy of
species with significant transition state dissociation of
the carbon-alkoxide bond. Peroxycarbenium ions have
been previously postulated as intermediates in reactions
of peroxyacetals and similar structures17,39,61 and are
analogous to the oxycarbenium ions postulated for the
related displacements of acetals.62 However, significant
(63) Patnaik, P. A Comprehensive Guide to the Hazardous Properties
of Chemical Substances; Van Nostrand Reinhold: New York, 1992.
(64) Medard, L. A. Accidental Explosions: Types of Explosive
Substances; Ellis Horwood Limited: Chichester, 1989; Vol. 2.
(65) Shanley, E. S. In Organic Peroxides; Swern, D., Ed.; Wiley-
Interscience: New York, 1970; Vol. 3, p 341.
(66) Sharpless, K. B.; Verhoeven, T. R. Aldrichimica Acta 1979, 12,
63.
(61) Rieche, A. Angew. Chem. 1961, 73, 57.
(62) Sammakia, T.; Smith, R. S. J . Am. Chem. Soc. 1994, 116, 7915.
(67) J ones, C. W. Applications of Hydrogen Peroxide and Derivatives;
Royal Society of Chemistry: Cambridge, 1999.

Peroxycarbenium-Mediated C-C Bond Formation
J . Org. Chem., Vol. 65, No. 25, 2000 8413
oxide (2b)11 and (3R,6S)- and (3S,6S)-3-methoxy-6-pentyl-
3,6,dihydro-1,2-dioxine (40)20 were prepared using reported
procedures.
in vacuo. Purification by flash chromatography (5% EA/hex)
afforded peroxide 13 (79 mg, 86%: Rf ) 0.65 in 10% EA/hex;
1H NMR δ 5.85 (m, 1H), 5.07-5.01 (m, 2H), 3.92 (t, 2H, J )
6.7), 2.31 (d, 2H, J ) 7.4), 1.59 (m, 2H), 1.35-1.20 (m, 10H),
1.18 (s, 6H), 0.86 (t, 3H, J ) 6.7); 13C NMR δ 134.4, 117.5,
81.7, 74.9, 43.6, 31.8, 29.4, 29.2, 27.8, 26.2, 24.2, 22.6, 14.0.
Anal. Calcd for C14H28O2: C, 73.63; H, 12.36. Found: C, 73.68;
H, 12.40.
Bis(1,1-d ioxyoctyl)-2-p r op a n e (14): Rf ) 0.55 in 10% EA/
hex; 1H NMR δ 4.04 (t, 2H, J ) 6.7), 1.59 (m, 4H), 1.42 (s,
6H), 1.33-1.25 (20H), 0.87 (t, 6H, J ) 6.7): 13C NMR δ 108.5,
75.4, 31.8, 29.4, 29.2, 27.8, 26.1, 21.4, 14.0. Anal. Calcd for
Gen er a l P r oced u r e for Syn th esis of Hyd r op er oxy-
a ceta ls. 4-ter t-Bu tyl-1-m eth oxycycloh exyl Hyd r op er ox-
id e (4a ). Into a -78 °C solution of 1-(methoxymethylene)-4-
tert-butylcyclohexane (63 mg, 0.35 mmol) in methanol (20 mL)
was passed a gaseous stream of O3/O2 until a blue color
persisted. The reaction mixture was then flushed with O2 to
dissipate the blue color and concentrated behind a shield. The
residue was purified by flash chromatography with 10% EA/
hexanes to yield 66 mg (95%) of hydroperoxyacetal 4a as a
2:1 mixture of diastereomers: Major diastereomer (from
mixture): Rf ) 0.3 in 11% EA/hexanes; 1H NMR δ 7.42 (s, 1H,
-OOH), 3.29 (s, 3H), 2.12 (m, 2H), 1.63 (m, 2H), 1.31 (m, 2H),
1.07-1.23 (m, 2H), 0.95 (m, 2H), 0.87 (s, 9H); 13C NMR δ 105.5,
48.1, 47.5, 31.4, 30.9, 27.5, 23.4; IR (neat) 3353 cm-1. Anal.
Calcd for C11H22O3: C, 65.32; H, 10.95. Found C, 65.50; H,
10.77. Minor diastereomer (from mixture): Rf ) 0.3 in 11%
C
12H26O3: C, 68.63; H, 12.12. Found: C, 68.37; H, 12.05.
Allyla tion of P er oxya ceta ls. Meth od A. To a -78 °C 0.1
M solution of peroxyacetal in dry CH2Cl2 was added TiCl4 (75
µL) followed, after 1-2 min, by allyltrimethylsilane (0.33 mL,
1.9 mmol). The reaction mixture was stirred for 30 min at -78
°C and quenched with saturated aqueous NH4Cl. Workup and
purification were conducted as for the monoperoxyketals.
Meth od B. Lewis acid was added at -78 °C, followed by
warming to desired temperature.
1
EA/hexanes; H NMR δ 7.44 (s, 1H, OOH), 3.33 (s, 3H), 2.22
(m, 2H), 1.63 (m, 2H), 1.31 (m, 2H), 1.07-1.23 (m, 2H), 0.95
(m, 2H), 0.87 (s, 9H); 13C NMR δ 105.3, 48.4, 47.4, 32.2, 30.9,
27.5, 23.6.
((1,1-Dim eth yleth yl)d im eth ylsilyl)-1-octen -4-yl p er ox-
1
id e (19): Rf ) 0.70 in EA/hex; H NMR δ 5.80 (tdd, 1H, J )
Syn th esis of P er oxya ceta ls via Alk yla tion of Hyd r o-
p er oxya ceta ls. 2-Meth oxyp r op -2-yl-4-m eth yl-3-p en ten yl
p er oxid e (1e). To a 0 °C solution of 5-bromo-2-methyl-2-
pentene (2.0 g, 12 mmol) in DMF (20 mL) under N2 was added
a solution of crude 2-methoxyprop-2-yl hydroperoxide 1a (2.7
g, 20 mmol) in DMF (5 mL) followed by CsOH (2.4 g, 14 mmol).
The resulting solution was stirred for 2 h at 0 °C and then
quenched with water (150 mL). The mixture was extracted
with ether (3 × 150 mL), and the combined organic layers were
dried over Na2SO4. After removal of solvent in vacuo, the
residue was subjected to flash chromatography (5% EA/hex)
to afford the peroxide (1.7 g, 75%) as a colorless oil: Rf ) 0.38
(5% EA/hex); 1H NMR δ 5.12 (app t of hept, 1 H, J ) 7.2, 1.4),
3.98 (t, 2 H, J ) 7.6), 3.32 (s, 3 H), 2.33 (q, 2 H, J ) 7.2), 1.70
(s, 3 H), 1.63 (s, 3 H), 1.40 (s, 6 H); 13C NMR δ 133.9, 119.6,
104.6, 74.7, 49.1, 26.9, 25.6, 22.7, 17.7. Anal. Calcd for
7.2, 10.3, 17.2), 5.07 (dd, 1H, J ) 10.2, 1.4), 5.02 (dd, 1H, J )
17.2, 1.4), 3.90 (tt, 1H, J ) 6.2, 5.5), 2.42 (td, 1H, J ) 5.2,
1.2), 2.29 (tt, 1H, J ) 6.2, 1.2), 1.60-0.85 (9H), 0.89 (s, 9H),
0.17 (s, 3H), 0.16 (s, 3H); 13C NMR δ 134.8, 116,8, 84.7, 36.9,
31.4, 27.6, 26.2, 22.8, 13.2, 13.9, -5.7. Anal. Calcd for C14H30O2-
Si: C, 65.06; H, 11.70. Found: C, 65.33; H, 11.63.
Dep r otection of Silyl P er oxid es. 1-Octen -3-yl Hyd r o-
p er oxid e (24). To a solution of silylated peroxide (19) (115
mg, 1.0 equiv) in THF (0.4 mL, 1 M) was added tetrabutyl-
ammonium fluoride (0.42 mL, 1.0 equiv, 1 M in THF). The
reaction was quenched after 20 min with saturated NH4Cl.
The ethyl acetate extracts were washed with brine and dried
over anhydrous Na2SO4. Concentration, followed by flash
chromatography (10% EA/hex), furnished 56.5 mg (93.5%) of
1
hydroperoxide 22: Rf ) 0.78 in 10% EA/hex; H NMR δ 7.80
(s, 1H), 5.85 (m, 1H), 5.10 (m, 2H), 3.99 (p, 1H, J ) 6.7), 2.40
C
10H20O3: C, 63.79; H, 10.71. Found: C, 64.00; H, 10.56.
(m, 2H), 1.65-1.25 (6H), 0.92 (t, 3H, J ) 6.9); 13C NMR δ 134.6,
Syn th esis of Silyl P er oxya ceta ls fr om Hyd r op er oxy-
117.2, 84.9, 36.9, 31.3, 27.6, 22.7, 13.9; IR (neat) 3405 cm-1
.
a ceta ls. To a 0 °C solution of hydroperoxyacetal (1 equiv) in
DMF/CH2Cl2 (1:5, 1.0 M) was added imidazole (1.1 equiv)
followed by TBDMS-Cl (1.5 equiv). The reaction was monitored
by thin-layer chromatography and was quenched with water.
The dried hexane extract was concentrated and purified by
flash chromatography (5% EA/hex) to give the silylated hy-
droperoxy acetals.
Rea ction of P er oxya ceta ls w ith Silyl En ol Eth er s. To
a 0.1 M solution of peroxyacetal (1 equiv) and silyl enol ether
(1 equiv) in CH2Cl2 at the indicated temperature was added
TiCl4 (1 equiv), SnCl4 (1 equiv), or TMSOTf (5-10 mol %). After
1 h, the reaction was quenched by addition of saturated
aqueous NH4Cl solution. The hexane extract was dried over
Na2SO4 and concentrated. The peroxides were purified by flash
chromatography.
((1,1-Dim et h ylet h yl)d im et h ylsilyl)-1-m et h oxyp en t yl
1
p er oxid e (6d ): Rf ) 0.76 in 10% EA/hex; H NMR δ 4.73 (t,
4-Meth yl-4-octyld ioxy-2-p en ta n on e (30): Rf ) 0.35 in
20% EA/hex; 1H NMR δ 3.89 (t, 2H, J ) 6.6), 2.68 (s, 2H), 2.17
(s, 3H), 1.55 (m, 2H), 1.26-1.24 (16 H), 0.86 (t, J ) 6.7,
terminal Me); 13C NMR δ 207.5, 80.9, 74.9, 51.8, 31.9, 31.8,
1H, J ) 5.5), 3.54 (s, 3H), 1.60-0.85 (9H), 0.94 (s, 9H), 0.17
(s, 3H), 0.16 (s, 3H); 13C NMR δ 109.1, 57.1, 31.8, 26.9, 26.1,
22.5, 18.1, 13.9, -5.7. Anal. Calcd for C12H28O3Si: C, 58.02;
H, 11.36. Found: C, 58.14; H, 11.51.
29.4, 29.1, 27.7, 26.1, 24.6, 22.6, 14.0; IR (neat) 1712 cm-1
;
Syn th esis of P er oxya ceta ls via Aceta liza tion of En ol
Eth er s. 1-(1-Meth oxycycloh exyl)octyl P er oxid e (4b). To
a solution of octyl hydroperoxide (1.46 g, 10 mmol)10 in CH2-
Cl2 was added 1-methoxy-1-cyclohexene (1.23 g, 1.1 equiv) and
pyridinium p-toluenesulfonate (30 mg). After stirring for 2 h,
the reaction was quenched with water and extracted with
hexane. The organic layer was dried, and the solvent was
removed. The residue was subjected to flash chromatography
(5% EA/hex) to afford peroxide 4b (2.38 g, 92%): Rf ) 0.50 in
10% EA/hex; 1H NMR δ 4.00 (t, 2H, J ) 6.7), 3.29 (s, 3H),
1.71-1.26 (m, 22H), 0.86 (t, 3H, J ) 6.7); 13C NMR δ 104.5,
74.8, 47.9, 31.7, 31.5, 29.3, 29.0, 27.8, 26.0, 25.4, 22.6, 22.4,
13.8. Anal. Calcd for C15H30O3: C, 69.72; H, 11.70. Found: C,
69.50; H, 11.90.
HRMS m/z calcd for C17H33O3 (M + H) 245.2117, found
245.2114. Anal. Calcd for C14H28O3: C, 68.81: H, 11.55.
Found: C, 68.63; H, 11.63.
Rea ction of P er oxya ceta ls w ith Silyl Keten e Aceta ls.
To a 0 °C solution of peroxyacetal (1 equiv) in CH2Cl2 (0.1 M)
was added the silyl ketene acetal (1 equiv, prepared by
reported procedures) followed by TMSOTf (0.1 equiv). The
reaction was monitored by TLC and then quenched with
saturated aqueous NaHCO3. The aqueous layer was extracted
twice with ethyl acetate, and the organic layers were washed
with brine and dried over anhydrous Na2SO4. The concentrated
residue was purified by flash chromatography with EA/
hexanes.
Gen er a l P r oced u r e for Allyla tion of Mon op er oxyk e-
ta ls. (2-Meth yl-4-p en ten -2-yl)octyl P er oxid e (13). To a -78
°C solution of perketal 1b (87 mg, 0.4 mmol) in CH2Cl2 (3 mL)
was added TiCl4 (0.4 mmol) under N2. After 3 min, a solution
of allyltrimethylsilane (59 mg, 1.3 equiv) in CH2Cl2 (1 mL) was
added. The solution was stirred for 1 h and then quenched
with water. The hexane extract was dried and concentrated
Eth yl 2-m eth yl-3-[((1,1-Dim eth yleth yl)d im eth ylsilyl)-
d ioxy]h ep ta n oa te (33): Rf ) 0.53 in 10% EA/hex. Anal. Calcd
for C15H34O4Si: C, 60.33; H, 10.76. Found: C, 60.24; H, 10.74.
Anti (determined from mixture): 1H NMR δ 4.23 (m, 1H), 4.10
(m, 2H), 3.08 (qd, 1H, J ) 7.16, 5.60), 1.08 (d, 3H, J ) 7.16),
1.40-0.80 (18H), 0.8 (s, 6H). Syn (determined from mixture):
Rf ) 0.53 in 10% EA/hex; 1H NMR δ 4.10 (m, 2H + 1H, OCH2-

8414 J . Org. Chem., Vol. 65, No. 25, 2000
Dussault et al.
CH3, CH(OOTBS)), 2.64 (qd, 1H, J ) 7.2, 4.4), 1.15 (d, 3H,
J ) 7.2), 1.40-0.80 (18H), 0.8 (s, 6H).
retention time 10.2 min). Cis: Rf ) 0.43 (5% EA/hex); 1H NMR
δ 4.34-4.26 (m, 1 H), 4.21-4.08 (m, 2 H), 2.08-1.77 (m, 5 H),
1.66 (s, 3 H), 1.63 (s, 3 H), 1.58-1.25 (m, 4 H), 0.91 (t, 3 H,
J ) 7.2); 13C NMR δ 82.9, 72.8, 70.9, 47.6, 32.7, 32.4, 30.6,
27.7, 24.2, 22.6, 14.0. Anal. Calcd for C11H21O2Cl: C, 59.85;
H, 9.59. Found: C, 59.91; H, 9.62. Trans: Rf ) 0.41 (5% EA/
hex); 1H NMR (300 MHz) δ 4.31 (m, 1 H), 4.24-4.15 (m, 2 H),
2.36 (m, 1 H), 2.25-2.10 (m, 2 H), 1.74-1.55 (m, 2 H), 1.61 (s,
3 H), 1.60 (s, 3 H), 1.50-1.25 (m, 4 H), 0.93 (t, 3 H, J ) 7.2);
13C NMR δ 82.5, 72.5, 70.4, 49.2, 31.6, 30.7, 27.8, 26.6, 22.5,
22.4, 14.1.
Com p et it it on b et w een Cycliza t ion a n d Allyla t ion .
1-(2-Met h yl-5-p en t en yl)-4-m et h yl-3-p en t en yl P er oxid e
(52). To a -78 °C solution of peroxyacetal 1e or 3e in CH2Cl2
under N2 was added allyltrimethylsilane (1 equiv), followed
by a 1 M solution of TiCl4 in CH2Cl2 (1 equiv). The resulting
solution was stirred for 30 min at -78 °C. Workup as before
followed by flash chromatography (2.5% EA/hex) afforded 52:
Rf ) 0.65 (2.5% EA/hex); 1H NMR (500 MHz) δ 5.81 (m, 1 H),
5.11 (t, 1 H, J ) 6.9), 5.06 (s, 1 H), 5.03 (d, 1 H, J ) 5.6), 3.90
(t, 2 H, J ) 7.1), 2.31 (d, 2 H, J ) 7.3), 2.28 (app. q, 2 H, J )
6.8), 1.69 (s, 3 H), 1.62 (s, 3 H), 1.19 (s, 6 H); 13C NMR (125
MHz) δ 134.4, 133.8, 119.9, 117.4, 81.8, 74.5, 43.7, 26.9, 25.7,
24.2, 17.7. Anal. Calcd for C12H22O2: C, 72.68; H, 11.18.
Found: C, 72.64; H, 11.37.
Syn th esis of 1,2-Dioxola n es via Allyla tion of Hyd r o-
p er oxya ceta ls. Meth od A. To a -78 °C solution of freshly
prepared 2-methoxyprop-2-yl hydroperoxide 1a (10.2 mmol)
and allyltrimethylsilane (4.2 mL, 26.5 mmol) in CH2Cl2 (150
mL) was rapidly added TiCl4 (10.2 mL of a 1 M CH2Cl2
solution). The reaction mixture was stirred for 25 min,
quenched with water (5 mL), and allowed to warm to RT. The
organic layer was separated, and the aqueous layer was
extracted with CH2Cl2 (1 × 20 mL). The combined organic
layers were dried over Na2SO4 and concentrated. Flash chro-
matography with 2% EA/hexanes afforded 595 mg (31%) of
dioxolane. Addition of TiCl4 prior (3 min) to allyltrimethyl-
silane furnished the same product in 14% yield. Slow addition
(10 min) of TiCl4 resulted in a 4% yield. Meth od B. To a -78
°C solution of freshly prepared 2-(2-methoxyethoxy)prop-2-yl
hydroperoxide 2a (1.566 gm, 10.44 mmol) and allyltrimethyl-
silane (4.5 mL, 28.2 mmol) in CH2Cl2 (150 mL) was rapidly
added SnCl4 (10.4 mL of a 1 M solution in CH2Cl2). The
reaction mixture was stirred for 4 h, worked up, and purified,
as before, to afford 1.1 g (56%) of dioxolane 39.
3,3-Dim eth yl-5-tr im eth ylsilylm eth yl-1,2-dioxolan e (39):
1
Rf ) 0.4 in 11% EA/hexanes; H NMR (500 MHz) δ 4.35 (m,
1H), 2.41 (dd, 1H, J ) 6.8, 11.2), 1.88 (dd, 1H, J ) 8.0, 11.6),
1.35 (s, 3H), 1.31 (s, 3H), 1.08 (dd, 1H, J ) 5.2, 14.1), 0.88 (dd,
1H, J ) 9.6, 14.1), 0.03 (s, 9H); 13C NMR (125 MHz) δ 83.5,
80.1, 54.5, 27.6, 25.7, 21.3, -1.0; IR (neat) 1182 cm-1. Anal.
Calcd for C19H20O2Si: C, 57.28; H, 10.05. Found C, 57.30; H,
10.55.
Ack n ow led gm en t. This work was supported by the
National Institutes of Health (GM45571). NMR spec-
trometers were purchased with funds from an NIH
Shared Instrumentation Program (SIG-1-510-RR06307).
We thank Prof. Richard Shoemaker for assistance with
NMR experiments and Mr. Yang Suh for investigations
of dioxine reactivity.
Cycliza tion of Un sa tu r a ted P er oxya ceta ls. cis- a n d
tr a n s-3-Bu tyl-4-(2-ch lor op r op -2-yl)-1,2-d ioxa n e (46). To a
-78 °C solution of 5-(1-methoxypentyl)dioxy-2-methyl-2-pen-
tene 6e (220.0 mg, 1.0 mmol) in CH2Cl2 (20 mL) under N2 was
added a solution of SnCl4 in CH2Cl2 (2.0 mL, 1.0 M, 2.0 mmol).
The resulting solution was stirred for 4 h at -78 °C. Workup
as before was followed by flash chromagraphy (5% EA/hex) to
furnish a mixture of diastereomers, which could be separated
by HPLC (5% EA/hex) to afford cis-46 (107.4 mg, 49%,
retention time 9.1 min) followed by trans-46 (41.6 mg, 19%,
Su p p or tin g In for m a tion Ava ila ble: Standard experi-
mental procedures, selected preparations, and spectral listings
(1H, 13C, and IR) for all new compounds. This material is
available free of charge via the Internet at http://pubs.acs.org.
J O991714Z