Applied photochemistry - Light controlled perfume release

Article abstract of DOI:10.2533/chimia.2007.665

Ambient light is one of the most suitable available trigger conditions for the release of covalently bound volatile odorants in home- and laundry-care applications. We report on three complementary classes of light-cleavable fragrance precursors, covering the controlled release of odorants with a wide range of functional groups. o-Hydroxy cinnamates 1 undergo a UV-induced double bond isomerization followed by transesterification to release coumarin and a fragrance alcohol of choice. α-Alkoxyacetophenones 10 and α,α-dialkoxyacetophenones 12 undergo Norrish type II fragmentations upon UV-irradiation, thereby releasing one or two equivalents of fragrant aldehydes, respectively. Finally, photoexcited Xanthenoic esters 22 undergo fragmentation to release reactive acyl radicals, which further cyclize onto internal olefins to form perfumery lactones of various ring sizes. Schweizerische Chemische Gesellschaft.

Full text of DOI:10.2533/chimia.2007.665

PHOTOCHEMISTRY
665
doi:10.2533/chimia.2007.665
CHIMIA 2007, 61, No. 10
Chimia 61 (2007) 665–669
© Schweizerische Chemische Gesellschaft
ISSN 0009–4293
Applied Photochemistry − Light Controlled
Perfume Release
Samuel Derrera, Felix Flachsmann*a, Caroline Plessisb, and Melanie Stangc
Abstract: Ambient light is one of the most suitable available trigger conditions for the release of covalently bound
volatile odorants in home- and laundry-care applications. We report on three complementary classes of light-cleav-
able fragrance precursors, covering the controlled release of odorants with a wide range of functional groups.
o-Hydroxy cinnamates 1 undergo a UV-induced double bond isomerization followed by transesterification to re-
lease coumarin and a fragrance alcohol of choice. α-Alkoxyacetophenones 10 and α,α-dialkoxyacetophenones
12 undergo Norrish type II fragmentations upon UV-irradiation, thereby releasing one or two equivalents of fragrant
aldehydes, respectively. Finally, photoexcited Xanthenoic esters 22 undergo fragmentation to release reactive acyl
radicals, which further cyclize onto internal olefins to form perfumery lactones of various ring sizes.
Keywords: Fragrance precursor ⋅ Light cleavable ⋅ Norrish type II ⋅ Photoisomerization ⋅ Pro-perfume
1. Introduction
OH
h%
OH
O
O
O
Improving perfume longevity is a prime
research goal in the fragrance industry. In
the world of perfumed consumer products,
this implies mainly the prevention of loss-
es of perfume during storage (premature
evaporation, chemical degradation) and
application (low affinity to substrate, wash-
out in surfactant-rich aqueous phases and
O
R
O
R
R
OH
O
1
2
3
Scheme 1. Photoisomerization and lactonization of E-o-hydroxy cinnamates. Substituents on the
aromatic rings are omitted for the sake of clarity.
evaporation during the drying process). The
physical and olfactory parameters which
determine the longlastingness of each indi-
vidual fragrance ingredient in a given ap-
plication (referred to also as substantivity)
differ widely across olfactory and structural
classes. Numerous highly substantive com-
pounds are found among woody, ambery
and musky odorants,[1] whereas molecules
exhibiting floral, fruity, aldehydic or green
notes, essential for transmitting freshness
and cleanliness, are often relatively small,
have gained considerable experience in
the photochemical behavior of substituted
cinnamates (e.g. ethyl hexyl methoxycin-
namate,commercializedasParsolMCX™),
which, upon UV-irradiation, undergo E/Z-
isomerization via the excited triplet state.
In the special case of ortho-hydroxy cin-
namates (coumarates), 1, the Z-isomer is
unstable because of the spatial proximity of
the ester group and the phenolic hydroxyl
group, leading to fragmentation of the mol-
ecule into coumarin 3 (which may carry
additional substituents) and the alcohol
moiety (Scheme 1).
This potentially very useful transfor-
mation has been scarcely mentioned in the
volatile and sufficiently water-soluble to be
lost in dilute aqueous applications.
In order to overcome this substantivity
problem, the use of fragrance precursors
(also referred to as profragrances or pro-
perfumes) has been envisaged, in which
odorants are bound to a larger molecular
backbone, from which they are slowly re-
leased via hydrolytic, enzymatic, thermal
or photolytic cleavage mechanisms. For
consumer product applications, light is an
ideal physical trigger, since it can be eas-
ily excluded during storage and is generally
present when perfume release is expected.
In the following account, we describe three
classes of fragrance precursors, in which
photoexcitation leads directly to fragmen-
tation according to a Norrish type II mech-
anism or, alternatively, produces unstable
species, which ultimately break apart to
release the fragrance molecules.
literature. The first study was reported in
1934 by Dey et al.,[2] who found that light-
inducedlactonizationwasmuchcleanerand
faster than the thermally induced process.
E-coumarates as photolytically removable
‘blocking’ groups for thrombine and other
enzymes have been reported by Porter and
coworkers.[3] Wang and coworkers studied
Z-coumarates as lipase-cleavable protect-
ing groups for alcohols,[4] whereas E-o-hy-
droxy cinnamic amides have been proposed
*Correspondence: Dr. F. Flachsmanna
Tel.: +41 44 824 2324
Fax: + 41 44 824 2926
E-Mail: felix.flachsmann@givaudan.com
aGivaudan Schweiz AG
Fragrance Research
Ueberlandstrasse 138
CH-8600 Dübendorf
2. o-Hydroxy Cinnamic Acid Esters
bCurrent address: Mane, 620 Route de Grasse,
06620 Le Bar-Sur-Loup, France
cCurrent address: Novartis Pharma AG,
Lichtstrasse 35, CH-4056 Basel
In the course of our long-standing re-
search program on sunscreen agents, we

PHOTOCHEMISTRY
666
CHIMIA 2007, 61, No. 10
diation of its 7'-methoxy analogue 7 leads
to a rapidly decreasing conversion rate with
1. NaH, "
2. H3O+
OH
O
O
build up of Z-7. This might be due to the re-
duced electrophilicity of the ester group, but
also of a possible interference of the product,
7-methoxycoumarin (methylumbelliferon),
R1
R1
+
R
OH
O
R
O
1
3
with the photoisomerization of the start-
ing material (internal quenching of excited
states). In the case of the corresponding o-
1. R-OH, pyridine, DMAP
2. TBAF
t-butyl derivative 8, the lactonization rate
is reduced, most probably as a result of the
steric compression occurring upon attack of
the phenolic hydroxyl group to the ester to
OTBDMS
OTBDMS
OTBDMS
Cl
(COCl)2
R1
R1
form a tetrahedral intermediate (‘buttress-
O
O
5
4
ing effect’[8]). Finally, the dependence of the
rate of saponification or transesterification
on the steric bulk of the alcohol moiety to
Scheme 2. Preparation methods of E-coumarates
be exchanged has been described and rules
established (e.g. Newman’s empirical ‘rule
of six’[9]). Thus, upon irradiation of the di-
hydromyrcenyl coumarate 9 for 30 min., a
by the same group as light-cleavable pro-
tecting groups for amines.[5]
The isomerization and fragmentation
of a large series of E-coumarates under ir-
radiation in a photoreactor was monitored
in a time-resolved manner. We found that
reaction rates are, as expected, highly struc-
ture dependant. Four typical examples are
represented in Fig. 1.
Under the relatively harsh irradiation
conditions employed, the transformation
of E-coumarates of primary alcohols into
coumarin and the alcohol generally reaches
mixture is formed containing 57% Z- and
only 34% E-coumarate (a roughly 2:1 ratio
of Z:E in the photoequilibrium state has also
been found for other slowly- or non-lac-
tonizing coumarates). Lactonization of an
isolated sample of the Z-isomer kept away
from light takes a full week.
We became interested in E-coumarates
in the context of controlled fragrance re-
lease, since these compounds offer the
unique possibility of delivering coumarin
and a fragrance alcohol from a single pre-
cursorstructurewithnoadditionalweight.[6]
Coumarin is a highly appreciated fragrance
ingredient used in many different olfactory
themes, but lacks substantivity in rinse-off
We are thus able to control the rate of
perfume release over a wide range of time
through proper choice of the bulkiness of
applications. The same holds true for many
completion within 10−20 min, as exempli-
fied by the irradiation of 9-decenyl-E-cou-
marate (6, λmax 326 nm, ε 135'914). Irra-
the attached fragrance alcohol.
valuable perfumery alcohols and phenols.
For the preparation of perfumistically
interesting E-coumarates, we have em-
ployed two main synthetic routes which are
summarized in Scheme 2.
During these studies, we also recorded
preliminary data showing a negative influ-
A few entries in the literature on the
direct reaction of coumarin with large ex-
cesses of sodium methoxide, e.g.[7] to yield
the corresponding methyl E-coumarates,
have prompted us to explore this reaction
with sodium salts of perfumery alcohols.
We were pleased to find that simply react-
ing coumarin with 1−2 equiv. of the so-
dium salt of primary, secondary and even
tertiary perfumery alcohols in a variety of
non-protic solvents furnished, after hydro-
lysis, the desired E-coumarates in useful to
excellent yields. Hence, in terms of mate-
rials, preparation of and fragrance release
from E-coumarates are symmetrical to each
other, the former being a thermal, alkali-
promoted process, the latter a photochemi-
cal one, but both featuring an E/Z-double
bond isomerization as the key element.
Unfortunately, the small but noble group of
phenolic perfumery raw materials, such as
vanillin or eugenol, does not react with cou-
OH
O
OH
O
O
O
O
6
7
100
80
60
40
20
0
100
80
60
40
20
0
0
10
20
30
0
10
20
30
[min]
[min]
OH
O
OH
O
O
O
8
9
100
80
100
80
60
60
40
40
marin to form E-coumarates. Therefore, we
developed a second route, which starts from
commercially available E-coumaric acid.
After bis-silylation, ester 4 is transformed
into acid chloride 5 and then coupled with
20
20
0
0
0
10
20
30
0
10
20
30
[min]
[min]
the phenolic fragrance ingredient. The final
Fig. 1. Photoisomerization/lactonization of different E-coumarates (0.5 mM solutions in CH3CN/H2O
deprotection step requires carefully con-
trolled conditions in order to avoid saponi-
fication of the fragile phenol esters.
9:1, irradiation in a Pyrex® photoreactor equipped with a 150 W mercury medium pressure lamp,
analysis by RP-HPLC). Green: E-coumarate Blue: Z-coumarate Red: (substituted) coumarin.

PHOTOCHEMISTRY
667
CHIMIA 2007, 61, No. 10
ence of UV-irradiation on the lactonization
rates. The underlying reason might be the
O
O
O
EtOH,
HBr conc.,
DMSO
OEt
well-documented photoenhanced acidity of
the phenolic OH-group,[10] leading to a less
nucleophilic phenolate. Additional studies
on this rather unexpected additional influ-
ence of light on perfume release are cur-
rently under way.
H+ cat.
OH
OEt
OH
14
13
R2
R1
O
R2
R1
O
R1 OH
H+ cat.
h%
O
O
2
+
R2 R1
O
- EtOH
3. Fragrance Precursors Based on
the Norrish Type II Photo-Cleavage
R2
12
Fragrance materials
The first Norrish type II-based fragrance
precursor system was devised by Anderson
Scheme 4. Synthesis of fragrance precursors 12 and photochemical odorant release. Substituents
on the aromatic rings are omitted for the sake of clarity.
and Fráter in 1998.[11] Other systems based
on the acetophenone motive[12] and α-ke-
toesters[13] have been studied by Herrmann
and coworkers. This family of α-alkoxy-
and concentrate the fragrant aspect on the cleavage. Thus, the phenacyl acetals 15 are
acetophenones 10 releases upon UV-light
irradiation acetophenones and either al-
dehydes or ketones depending on the na-
ture of the odiferous species to be released
from the alkoxy part (Scheme 3). A more
detailed description of the release mecha-
carbonyl compound to be released.
light-labile precursors for odoriferous es-
In this light, the system has subsequent- ters[17] and, accordingly, the respective cyc-
lic structures 16 for lactones.[18] The synthe-
sis of these species as well as their cleavage
is shown in Scheme 5. Key intermediate is
ly been further tuned to release two carbon-
yl compounds from one chromophore.[14]
The resulting α,α-dialkoxyacetophenone
structures 12, a simple representative being
the α-hydroxy-ketone 17, prepared from
nism is given below. The synthesis of 10 is
the diethoxyacetophenone, are well known
and used as starter for photoinitiated radical
polymerization.[15] Given the constraint that
a light-labile profragrance is expected to
cleave at natural or even artificial light with
the corresponding acetophenone by α-bro-
straightforward, starting with the alkoxyl-
ation of bromoacetonitrile with either a pri-
mary or a secondary alcohol derived from a
fragrant aldehyde or ketone respectively to
mination, formylation with sodium formate
in aqueous ethanol and subsequent hydro-
lysis. The alcohol 17 is then treated with
either linear or cyclic enol ethers under the
yield the nitrile 11. This is then followed by
a limited UV proportion, as opposed to in-
tense mercury lamps or UV lasers used for
the curing of monomers, a simple acetophe-
none was not entirely suitable as chromo-
catalytic action of trifluoroacetic acid, to af-
ford the required phenacyl acetals 15 or 16,
respectively.
The fragrance release mechanism (pho-
tolysis) of the above-described properfumes
the addition of a phenylmagnesium halide
and the hydrolysis of the so-obtained imine.
Evidently, the selection of the substitution
patternofthebenzeneringgovernsthechro-
mophoric properties of the fragrance pre-
cursor system and thus the potential ease of
cleavage. It is obviously desirable that both
fragments resulting from the Norrish type II
cleavage, namely the acetophenone part and
the aldehyde or ketone, be well-established
perfumery chemicals. However, in order to
optimize the photochemical performance
of the precursor, it may be more desirable
to choose a non-odoriferous chromophore
phore. Thus, a series of more electron-rich
is exemplified on the Lilial®-precursor 18,
benzeneringswithabathochromicshiftwas
employed: 4-alkoxy- (λmax approx. +30 nm
with the chromophore being p-propoxy-
vs acetophenone), 3,4-dialkoxy- (+60 nm),
acetophenone (λmax 278 nm, ε 17600). It
4-acylamino- (+45 nm), and 4-dialkylami-
has a very faint odor which does not disturb
the scent quality of Lilial® upon release. In
no- (+98 nm) substituted acetophenones.
The synthesis of these α,α-dialkoxyace-
the expected Norrish type II fragmentation
tophenones 12 differs significantly from
(Scheme 6), the ground state (S0) carbonyl
the above-described ethers 10, in which it
group is excited to the S1 state, upon which
usually starts from the acetophenone. These
an intersystem crossing gives rise to the
are oxidized to the corresponding hydrated
arylglyoxal 13, using the protocol of Floyd
et al., involving hydrobromic acid and di-
methyl sulfoxide.[16] Although not abso-
lutely necessary, but more convenient for
triplet carbonyl T
1, from which γ-hydrogen
abstraction (or 1,5-H shift) takes place.[19]
At this stage, two competing reactions are
occurring: on the one hand, the β-scission
required for Lilial® release, and on the
i. NaH,
R2
R2
ii.BrCH2CN
the reason of solubility, the intermediate 13 other hand, the intramolecular recombina-
R1
O
CN
R1
OH
is then first converted to the diethyl acetal
14, from which the fragrance precursors are
accessible via trans-acetalization with the
required fragrance aldehyde or ketone-de-
rived alcohols (Scheme 4).
In the course of this research, it became
desirable not only to release ketones and al-
dehydes, but also esters and lactones, which
are included among the most important
fragrance materials, especially for fruity
accords. Owing to the wide scope of the
Norrish type II reaction, the most evident
development was the substitution of the
beta-carbon atom in the skeleton 10 for an
oxygen, in order to give rise to esters upon
tion of the diradical 19 to the correspond-
ing oxetane 20. An experiment (Fig. 2), in
which a 0.1% solution of the precursor 18
in acetonitrile is irradiated with a mercury
11
O
O
R1
h%
PhMgBr
R2
medium pressure lamp (150 W) in a boro-
silicate (Pyrex®, cut off at approximately
10
300 nm) apparatus over a period of 40 min,
demonstrated that the two competing reac-
tions occur to a similar extent (analysis by
HPLC of samples taken every 5 min) and
O
O
+
R2 R1
that the rate of recovery (yield) lays in the
Fragrance materials
order of 45−60%.
Scheme 3. Synthesis of fragrance precursors 10
and photochemical odorant release. Substituents
on the aromatic rings are omitted for the sake of
clarity.
Evidently, the Norrish type II reaction is
not the only possible reaction to occur up-
on irradiation. The α-fragmentation, also

PHOTOCHEMISTRY
668
CHIMIA 2007, 61, No. 10
O
O
O
O
O
R2
R1
O
O
O
O
O
R1
h%
h%
R1
TFA cat.
Scheme 5. Synthesis
of fragrance precursors
15 and 16 and
+
+
1. Br2
R2
O
O
2. NaOCHO
EtOH aq.
R2
15
16
O
R1
OH
fragrant ester
photochemical release
of fragrant esters and
lactones. Substituents
on the aromatic rings
are omitted for the sake
of clarity.
( )n
TFA cat.
O
R1
O
R1
O
17
( )n
( )n
fragrant lactone
H
Norrish Type II
OH
O
ISC
$-H-abstraction
h%
O
O
So
S1
T1
19
PrO
PrO
#-cleavage,
18
recombination
tautomerization
O
PrO
+
O
HO
O
PrO
Scheme 6.
Photofragmentation of
Lilial®-precursor 18
Lilial ®
20
O
100
O
O
PrO
100
80
60
40
20
0
O
80
60
40
20
0
18
O
PrO
21
0
5
10
15
20
25
0
6.5
10
15
20
25
30
35
40
min
min
Fig. 2. Kinetic study of the photorelease of Lilial® (blue), 4-pro-
poxyacetophenone (red) and Oxetane 20 (yellow) from their precursor 18
Fig. 3. Kinetic study of the photorelease of Lilial® (blue) and 4-pro-
poxyacetophenone (red) from their precursor 21
termed Norrish type I cleavage, is also ex- of the required aldehyde (15%) and ace-
4. Fragrance Precursors Based on
pected in such compounds.[15] This is ob-
tophenone (2%!) are an indication of an
Xanthate Esters
served especially with the α,α-dialkoxy- unwanted photodegradation of either the
precursor or the products or both. In addi-
tion, the expected intermediate mono-alk-
acetophenones 12, and the corresponding,
relatively long lived benzoyl and dialk-
As part of our efforts to find alternative
photocleavable fragrance precursors, we
also envisaged that xanthenoic esters may
oxymethyl radicals, are believed to be the oxy-acetophenone 18 was not observed.
reason for their good performance as pho- This leads to the hypothesis that the pho-
release fragrant alcohols, based on a disclo-
toinitiators in the radiation curing of e.g. tolysis of the latter is significantly faster
sure of Barton et al., who observed the pho-
than that of the dialkoxyacetophenone 21. tolytic cleavage of xanthenoic aryl esters
Nevertheless, application tests have dem- into xanthene and the corresponding phe-
onstrated that the release of Lilial® from nols.[21] We expected that such esters would
its precursor 21 is sufficient to obtain an
olfactory signal that, in terms of longevity,
can easily compete with the effect of the
free fragrance material. It should thus be
noted that the laboratory irradiation condi-
tions are rather harsh compared to natural
sunlight.
acrylate monomers.[20] For the fragrance
precursor purpose, this α-fragmentation is,
of course, absolutely undesirable as it does
not give rise to the required odorants. Per-
forming an analogous kinetic experiment
with the Lilial®-precursor 21 (λmax 285
nm, ε 24000), offered some evidence for
competing mechanisms (Fig. 3). Although
no products related to the fragments from
the α-scission have been isolated and char-
acterized, the rather low rate of recovery
be capable of releasing fragrant alcohols
by a homolytic cleavage of the CO−OAr
bond, according to the well precedented
photochemical Fries rearrangement,[22] fol-
lowed by decarbonylation. Not quite unex-
pectedly, however, we have discovered that
only a small amount of alcohol is formed
from alkenyl xanthenoic esters 22 (Scheme

PHOTOCHEMISTRY
669
CHIMIA 2007, 61, No. 10
menich SA; Chem. Abstr. 134, 300652.
[14 ] S. Derrer, M. Gautschi, EP 1262473, pri-
ority 30.5.2001, to Givaudan SA; Chem.
fabric in laundry care, skin and hair in per-
sonal care or hard surfaces in the applica-
tion of all purpose cleaning.
R2
R1
( )n
R3
h% (>300 nm)
Abstr. 138, 8276.
Thus, our examples demonstrate how
O
O
[15] J. E. Christensen, A. F. Jacobine, C. J. V.
the use of photochemistry adds a whole
new creative and technical dimension to the
traditional ways of fragrancing. As the first
commercial application of this research,
the coumarin/Rosalva precursor 6 has been
recently introduced into the perfumer’s pal-
Scanio, Radiation Curing 1981, 8, 4.
[16] M. B. Floyd, M. T. Du, P. F. Fabio, L. A.
O
O
Jacob, B. D. Johnson, J. Org. Chem. 1985,
50, 5022.
22
O
R1
[17 ] M. Gautschi, C. Plessis, S. Derrer, EP
1146033, priority 10.4.2000, to Givaudan
cyclization
R3
( )n
O
ette under the name of Tonkarose.
R2
SA; Chem. Abstr. 135, 308610.
[18] M. Gautschi, C. Plessis, S. Derrer, EP
Received: July 27, 2007
O
R2
O
1167362, priority 19.6.2000, to Givaudan
R2
R3
O
SA; Chem. Abstr. 136, 74334.
[19] P. J. Wagner, Acc. Chem. Res. 1971, 4,
and/or
R3
[1] For overviews on modern fragrance in-
O
R1
( )n
( )n
gredients: a) G. Fráter, J. Bajgrowicz, P.
Kraft, Tetrahedron 1998, 54, 7633; b) P.
R1
168.
[20] J. P. Fouassier, D. J. Lougnot, J. Chem.
Kraft, J. Bajgrowicz, C. Denis, G. Fráter,
Soc., Faraday Trans. 1 1987, 83, 2935.
Angew. Chem., Int. Ed. 2000, 39, 2980.
Scheme 7. Photochemical reaction of xanthenoic
esters 22 to produce lactones as major
products
[21] D. H. R. Barton,Y. L. Chow,A. Cox, G. W.
[2] B. B. Dey, R. H. R. Rao, T. R. Seshadri, J.
Kirby, J. Chem. Soc. 1965, 3571.
Ind. Chem. Soc. 1934, 743.
[22] H. Kobsa, J. Org. Chem. 1962, 27, 2293.
[3] a)A. D. Turner, S.V. Pizzo, G. W. Rozakis,
[23] C. Plessis, S. Derrer, Tetrahedron Lett.
N. A. Porter, J. Am. Chem. Soc. 1987, 109,
2001, 42, 6519.
1274; b) A. D. Turner, S. V. Pizzo, G. W.
7). The major products were found to be
Rozakis, N. A. Porter, J. Am. Chem. Soc.
lactones of various ring sizes, depending
on the location of the unsaturation in the
parent alcohols.[23] It is fair to say that for
both economical reasons and their limited
performance, these xantenoic esters have
little potential as commercial fragrance
1988, 110, 244; c) N. A. Porter, J. W. Thu-
ring, H. Li, J. Am. Chem. Soc. 1999, 121,
7716.
[4] a) B. Wang, J. Zhang, W. Wang, Bioorg.
Med. Chem. Lett. 1996, 6, 945; b)Y. Liao,
S. Hendrata, S. Y. Bae, B. Wang, Chem.
Pharm. Bull. 2000, 48, 1138.
[5] B. Wang, A. Zheng, Chem. Pharm. Bull.
precursors. Therefore, our efforts have not
proceeded beyond the ‘proof of concept’
stage.
1997, 45, 715.
[6] a) G. Fráter, D. Anderson, US 6096918,
priority13.2.1998, toGivaudanSA;Chem.
Abstr. 131, 170173; b) F. Flachsmann, J.-
P. Bachmann, WO 2005077881, priority
4. Conclusion
12.2.2004, to Givaudan SA; Chem. Abstr.
143, 229566.
[7] N. Cairns, L.M. Harwood, P. D. Astles,
Chem. Commun. 1986, 16, 1264.
[8] a) M. Rieger, F. H. Westheimer, J. Am.
As a novel approach to improve the lon-
gevity of perfumes, this account describes
three different photo-labile fragrance pre-
cursor types for the release of selected fra-
grance materials. Homolytic bond cleav-
ages from photoexcited radical species
occur in α-alkoxyacetophenones and xan-
Chem. Soc. 1950, 72, 19; b) for a modern
example: K. Maeda, Y. Okamoto, O. Tole-
dano, D. Becker, S. E. Biali, Z. Rappoport,
thate esters. The former lead to the efficient
J. Org. Chem. 1994, 59, 5473.
release of perfumery aldehydes, whereas
fragrant lactones of various ring sizes are
released from the latter via cyclization of
intermediate acyl radical species onto in-
ternal olefins. Mild irradiation conditions
induce an E/Z-double bond isomerization
in E-coumarates, followed by clean and ef-
ficient release of coumarin and a fragrance
[9] M. S. Newman, J. Am. Chem. Soc. 1950,
72, 4783.
[10] a) C. Sandorfy, Compt. Rend. 1951, 232,
841; b) H. Konschin, R. Lunnala, F. Sund-
holm, Suomen Kemistiseuran Tiedonanto-
ja 1973, 82, 8. c) S. C. Shim, J. W. Park, H.
S. Ham, J. S. Chung, Bull. Korean Chem.
Soc. 1983, 4, 45.
alcohol via a spontaneous intramolecular
transesterification.
[11] D.Anderson, G. Fráter, EP 983990, priori-
ty 4.9.1998, to Givaudan SA; Chem. Abstr.
The materials described in this overview
132, 194193.
offer not only the desired slow and/or timed
[12] a) B. Levrand, A. Herrmann, Flav. Frag.
release of fragrance ingredients, but as in
J. 2006, 21, 400. b) A. Herrmann, WO
the case of the α-alkoxyacetophenones,
2001096272, priority 11.06.2000, to Fir-
are also a means of protecting fragile per-
menich SA.
fume ingredients, such as aldehydes, which
[13] a) S. Rochat, C. Minardi, J.-Y. De Saint
are prone to oxidation in harsh consumer
Laumer, A. Herrmann, Helv. Chim. Acta
product bases (e.g. detergents). Moreover,
2000, 83, 1645; b) A. Herrmann, C. De-
profragrances are more substantive than the
bonneville,V. Laubscher, L.Aymard, Flav.
free fragrance materials, resulting in better
Frag. J. 2000, 15, 415. c) A. Herrmann,
deposition on the target support, such as
US 6218355, priority 21.05.1999, to Fir-