Exploratory studies of H-atom abstraction and silyl-transfer photoreactions of silylalkyl ketones and (silylalkyl)phthalimides

Article abstract of DOI:10.1021/jo9522623

Exploratory studies have been conducted to probe competitive H-atom abstraction and SET-promoted, silyl-transfer reactions of excited states of silylalkyl ketones and (silylalkyl)phthalimides. Photochemical investigations with the (silylalkyl)phthalimides have demonstrated that typical γ-H atom abstraction reactions occur upon irradiation in less polar and less silophilic solvents. In contrast, irradiation of these substances in polar-protic-silophilic solvents results in product formation via pathways involving SET-induced desilylation. Photoreactions of silylamido-aryl ketones in either nonsilophilic or silophilic solvents take place almost exclusively by sequential SET silyl-transfer routes to produce azetidine products. Finally, the chemical selectivities of photochemical reactions of silylpropyl-aryl ketones appear to depend on medium polarity and silophilicity. Irradiation of these substrates in less polar-nonsilophilic solvents leads to almost exclusive formation of acetophenone and vinyltrimethylsilane in essentially equal yields by a reaction pathway initiated by γ-H atom abstraction and 1,4-biradical fragmentation. However, irradiation of these substances in polar-silophilic solvents produces acetophenone and vinyltrimethylsilane in an ca. 1.7:1 ratio reflecting the fact that a silyl-transfer pathway competes with H-atom abstraction under these conditions.

Full text of DOI:10.1021/jo9522623

3304
J . Org. Chem. 1996, 61, 3304-3314
Exp lor a tor y Stu d ies of H-Atom Abstr a ction a n d Silyl-Tr a n sfer
P h otor ea ction s of Silyla lk yl Keton es a n d (Silyla lk yl)p h th a lim id es
Yean J ang Lee, Rong Ling, and Patrick S. Mariano*
Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742
Ung Chan Yoon,* Dong Uk Kim, and Sun Wha Oh
Department of Chemistry, College of Natural Sciences, Pusan National University, Pusan 609-735, Korea
Received December 27, 1995X
Exploratory studies have been conducted to probe competitive H-atom abstraction and SET-
promoted, silyl-transfer reactions of excited states of silylalkyl ketones and (silylalkyl)phthalimides.
Photochemical investigations with the (silylalkyl)phthalimides have demonstrated that typical γ-H
atom abstraction reactions occur upon irradiation in less polar and less silophilic solvents. In
contrast, irradiation of these substances in polar-protic-silophilic solvents results in product
formation via pathways involving SET-induced desilylation. Photoreactions of silylamido-aryl
ketones in either nonsilophilic or silophilic solvents take place almost exclusively by sequential
SET silyl-transfer routes to produce azetidine products. Finally, the chemical selectivities of
photochemical reactions of silylpropyl-aryl ketones appear to depend on medium polarity and
silophilicity. Irradiation of these substrates in less polar-nonsilophilic solvents leads to almost
exclusive formation of acetophenone and vinyltrimethylsilane in essentially equal yields by a reaction
pathway initiated by γ-H atom abstraction and 1,4-biradical fragmentation. However, irradiation
of these substances in polar-silophilic solvents produces acetophenone and vinyltrimethylsilane
in an ca. 1.7:1 ratio reflecting the fact that a silyl-transfer pathway competes with H-atom
abstraction under these conditions.
Sch em e 1
In tr od u ction
Perhaps the most general and certainly the most well-
explored reactions in organic photochemistry are initiated
by intramolecular hydrogen-atom abstraction by an
excited state of a carbonyl compound.1 This process
serves as the key chemical step in the familiar Norrish
Type II fragmentation and Yang cyclization reactions,2
both of which proceed via the intermediacy of 1,n-
diradicals (Scheme 1). A number of comprehensive
reviews of these photoreactions have appeared1 and in
these can be found thorough summaries of the vast
number of mechanistically intriguing features of the
carbonyl excited state H-atom abstraction process as well
as the chemical and physical characteristics of intermedi-
ate 1,n-diradicals. Since it is pertinent to the investiga-
tion described below, a discussion of a few of the features
of excited state carbonyl H-atom abstraction reactions
will be briefly presented here. First, the process occurs
efficiently from carbonyl n-π* triplet states owing to
their electron-deficient, oxy radical nature. Second, in
structurally unconstrained systems, intramolecular H-
atom abstractions display strong regiochemical prefer-
ences for γ-hydrogens as a result of transition state
oxygen-hydrogen distances3 and conformational issues.4
Third, as expected for the radical nature of the processes,
C-H bond dissociation energies are also influential in
determining regiochemistry. Last, a number of studies
in recent years have demonstrated that an indirect,
excited-state electron transfer (SET) pathway can be
followed in bringing about formal H-atom migration.1,5
This is the case for systems in which the carbonyl excited
state has a sufficiently high reduction potential and/or
in which a donor site of low oxidation potential is present
in the appended alkyl chain. As a result, SET can occur
to generate zwitterionic diradicals 1 (Scheme 2). Proton
transfer in 1 then yields the same types of 1,n-diradicals
that would have arisen by H-atom abstraction routes.
It is clear that the efficiencies of hydrogen migration
reactions proceeding by the sequential SET-proton-
X Abstract published in Advance ACS Abstracts, May 1, 1996.
(1) Wagner, P. J . Top. Curr. Chem. 1976, 66, 1. Wagner, P. J .
Rearrangements in Ground and Excited States; deMayo, P., Ed.,
Academic Press: New York, 1980; Vols. 42 and 43. Wagner, P. J .; Park,
B.-S. Organic Photochemistry; Padwa A., Ed.; Marcel Dekker,: New
York, 1991; Vol. 11.
(2) Yang, N. C.; Morduchowitz, A.; Yang, D.-D. H. J . Am. Chem.
Soc. 1963, 85, 1017.
(3) Scheffer, J . R.; Garcia-Garibay, M.; Nalamasu, O. Organic
Photochemistry, Padwa, A., Ed.; Marcel Dekker: New York, 1987; Vol.
8.
(5) Kanaoka, Y.; Migita, Y.; Sato, Y.; Nakai, H. Heterocycles 1974,
2, 621. Sato, Y.; Nakai, H.; Wada, M.; Ogiwara, H.; Mizoguchi, T.;
Migita, Y.; Hatanaka, Y.; Kanaoka, Y. Chem. Pharm. Bull. 1982, 30,
1639. Sato, Y.; Nakai, H.; Ogiwara, H.; Mizoguchi, T.; Migita, Y.;
Kanaoka, Y. Tetrahedron Lett. 1973, 4565. Kanaoka, Y.; Nagasawa,
C.; Nakai, H.; Sato, Y.; Ogiwara, H.; Mizoguchi, T. Heterocycles 1975,
3, 553.
(6) Yoon, U. C.; Mariano, P. S. Acc. Chem. Res. 1992, 25, 233.
Mariano, P. S. Acc. Chem. Res. 1983, 16, 130. Zhang, X.-M.; Yeh, S.-
R.; Hong, S.; Freccaro, M.; Albini, A.; Falvey, D. E.; Mariano, P. S. J .
Am. Chem. Soc. 1994, 116, 4211. d’Alessandro, N.; Albini, A.; Mariano,
P. S. J . Org. Chem. 1993, 58, 937.
(4) Wagner, P. S. Acc. Chem. Res. 1983, 16, 461.
S0022-3263(95)02262-6 CCC: $12.00 © 1996 American Chemical Society

H-Atom Abstraction and Silyl-Transfer Photoreactions
J . Org. Chem., Vol. 61, No. 10, 1996 3305
Sch em e 2
This and other observations led us to think about the
potential viability of silicon versions of excited-state
H-atom migration reactions. As depicted in Scheme 4,
TMS migration reactions of this type can be envisaged
as occurring directly by O-Si bonding in the carbonyl
excited states or by sequential SET-silyl-transfer routes.
In addition, under conditions where oxygen of the car-
bonyl anion radical is complexed to a Lewis acid or
H-bonded and where an alternate silophile is present in
the medium, another potential pathway open to the
zwitterionic diradical intermediates 9 is desilylation
followed by cyclization of the resultant diradical anion.
The latter process would represent a silicon analog of the
Yang photocyclization reaction.
Sch em e 3
Sch em e 4
transfer pathway are governed by the redox properties
of the excited carbonyl group and not its configuration
or multiplicity. Also, regiochemical preferences in pho-
toreactions of this type are determined by the location
of donor sites in the alkyl chain and the resultant kinetic
R-C-H acidities of cation radicals. Good examples of the
latter control are found in photoreactions of phthalimides
which contain arene, ether, thioether, or amine functions
in N-alkyl appendages.5 As demonstrated by the selec-
tive formation of the tricyclic amidol 4 from phthalimide
2 (Scheme 3), diradicals 3 formed by the photoinduced
sequential SET-proton-transfer sequence can be quite
different from those expected in direct H-atom abstrac-
tion reactions.
Studies in our laboratories during recent years have
concentrated on a number of SET-photochemical reac-
tions which are driven by nucleophile- or base-promoted
R-fragmentation reactions of cation radicals.6 One spe-
cific aim of our efforts in this area has been to gain an
understanding of factors which govern the nature and
dynamics of cation radical R-desilylation processes. This
work has led to the development of preparatively useful
SET photoreactions of allyl-, benzyl-, and aminosilanes.7
Recent observations made in these studies have given
rise to thoughts about potentially general and interesting
photoreactions of silicon substituted carbonyl compounds,
especially those which mimic the familiar Norrish Type
II and Yang cyclization processes. A specific, provocative
example is seen in the photochemistry of N-[(trimethyl-
silyl)methyl]phthalimide (5) in which the transient azome-
thine ylide 7 is produced by a route formally involving
excited-state carbon-to-oxygen migration of the TMS
group.8 This efficient process is quite unique in that it
does not have a “non-silicon” counterpart (i.e., N-meth-
ylphthalimide (6) does not produce ylide 8 upon irradia-
tion).
Simple bond energy considerations suggest the ther-
modynamic feasibility of excited-state reactions involving
simultaneous cleavage of a C-Si and formation of an
O-Si bond.9 Moreover, a few examples of related inter-
molecular reactions are known in which a TMS group is
transferred from a disilane to oxygen in quinone triplet
excited states.10 In addition, Ohashi11 has demonstrated
that alkylsilanes undergo photoreactions with polycy-
anoarenes by pathways involving SET from the σC-Si
bond to the arene singlet excited states followed by
nucleophile-induced C-Si bond cleavage and radical
coupling to the arene anion radical. When combined,
these findings lend credence to the possibilities embodied
in Scheme 4, and they suggest that a study of the
photochemistry of silicon-substituted carbonyl com-
pounds might be a fruitful avenue to new reaction
discovery. With this in mind we have conducted explor-
atory photochemical investigations with selected sub-
stances in this class including the phthalimides 10 and
11, R-amido ketones 12 and 13, and phenones 14-16.
(7) Ahmed-Schofield, R.; Mariano, P. S. J . Org. Chem. 1987, 52,
1478. Ho, G. D.; Mariano, P. S. J . Org. Chem. 1988, 53, 5113. J ung, Y.
S.; Mariano, P. S. Tetrahedron Lett. 1993, 34, 4611.
(8) Yoon, U. C.; Kim, D. U.; Woo, C. W.; Choi, Y. S.; Lee, Y. L.;
Ammon, H. L.; Mariano, P. S. J . Am. Chem. Soc. 1995, 117, 2698. Yoon,
U. C.; Cho, S. J .; Lee, Y. J .; Mancheno, J . M.; Mariano, P. S. J . Org.
Chem. 1995, 60, 2353.
(9) Clovin, E. Silicon in Organic Synthesis; Butterworth: London,
1981; Chapter 2.
(10) Alberti, A.; Dellonte, S.; Paradisi, C.; Roffia, S.; Pedulli, G. F.
J . Am. Chem. Soc. 1990, 112, 1123. Sakamoto, K.; Sakurai, H. J . Am.
Chem. Soc. 1991, 113, 1466.
(11) Krushin, S.; Masuda, Y.; Matsushita, K.; Nakadaira, Y.; Ohashi,
M. Tetrahedron Lett. 1990, 31, 6395.

3306 J . Org. Chem., Vol. 61, No. 10, 1996
Lee et al.
The results of this investigation are presented and
discussed below.12
Resu lts a n d Discu ssion
Syn th etic Issu es. The photochemical substrates
employed in this investigation were prepared by using
simple synthetic sequences (see Experimental Section
and below). For example, phthalimide 10 was synthe-
sized by a two-step route starting with conversion of
2-(trimethylsilyl)ethanol to its chloride followed by alkyl-
ation with potassium phthalimide. Similarly, phthal-
imidation of the 3-(trimethylsilyl)-1-propyl iodide, pre-
pared from the corresponding alcohol, provides 11.
Preparative routes to the silylamidophenones 12 and 13
began with the respective additions of phenyl and
2-naphthylmagnesium bromide to the known13 amido
aldehyde 17. The alcohols, 18 and 19, formed in this way
were then subjected to Swern oxidation to produce the
ketones 12 and 13.
change occurs in the product profile when photoreaction
of 10 is carried out in 9:1 acetone-MeOH. Under these
conditions, the benzazepinedione 20 is not produced and
instead the reduction and reductive coupling products,
22 and 23, are generated in respective isolated yields of
16% and 75%. We have also investigated the photochem-
istry of the non-silicon-containing analog of 10, N-
ethylphthalimide (24), for comparative purposes. Kanao-
ka and his co-workers15 reported earlier that irradiation
of 24 in either MeCN or t-BuOH solution leads to low
yielding (3-6%) generation of benzazepinedione 20.
Inefficient production of 20 is also observed (this work)
when an acetone solution of 24 is irradiated under
conditions identical to those used for photoreaction of the
silicon analog 10 (see above). In this solvent, the major
photoproduct of 24 is the acetone adduct 25 (29%) which
is formed along with 20 (4%) and phthalimide 26 (2%).
γ-(Trimethylsilyl)butyrophenone (14) was made by
using the route described previously by Kuivila.14 In an
analogous fashion, reaction of 4-(trimethylsilyl)butyroni-
trile with 2-naphthylmagnesium bromide followed by
aqueous NH4Cl hydrolysis provided the naphthone 15.
Finally, 4-cyanobenzoic acid was converted to the p-
cyanobutyrophenone 16 by treatment of the correspond-
ing acid chloride with [3-(trimethylsilyl)-1-propyl]mag-
nesium bromide.
Silyla lk lyl P h th a lim id e P h otoch em istr y. Explor-
atory photochemical studies were initiated with the
(silylalkyl)phthalimides 10 and 11. Preparative irradia-
tion (λ > 220 nm) of an MeCN solution (10 mM) of the
silylethyl analog 10 followed by chromatography on silica
gel leads to isolation of the benzazepinedione 20 (68%).15
Photoproduct 20 (41%) along with the adduct 21 (7%)
is produced when an acetone solution of 10 is subjected
to otherwise identical irradiation conditions. A dramatic
Preparative irradiation of the (silylpropyl)phthalimide
11 in either MeCN or acetone followed by chromato-
graphic separation on silica gel results in isolation of four
photoproducts comprised of the (silylmethyl)benzazepinedi-
one 27 (28% in MeCN, 22% in acetone), the bicyclic
amidol 28 (21%, 8%), and the (silylpropenyl) amidols 29
(11%, 28%), and 30 (6%, 9%).
The photochemistry of the non-silicon analog of 11,
N-propylphthalimide (31) has been studied previously by
Kanaoka and his co-workers.15 Irradiation of an MeCN
(12) Lee, Y. J .; Lee, C. P.; J eon, Y. T.; Mariano, P. S.; Yoon, U. C.;
Kim, D. U.; Kim, J . C.; Lee, J . G. Tetrahedron Lett. 1993, 34, 5855.
(13) J eon, Y. T.; Lee, C. P., Mariano, P. S. J . Am. Chem. Soc. 1991,
113, 8847.
(14) Kuivila, H. G.; Maxfield, P. L. J . Organomet. Chem. 1967, 10,
41.
(15) Kanaoka, Y.; Migita, Y.; Koyama, K.; Sato, Y.; Nakai, H.;
Mizoguchi, T. Tetrahedron Lett. 1973, 14, 1193.

H-Atom Abstraction and Silyl-Transfer Photoreactions
J . Org. Chem., Vol. 61, No. 10, 1996 3307
F igu r e 1. The results of 1H NMR monitoring experiments following the photoconversion of N-(silylethyl)phthalimide 10 to
benzazepinediones. Displayed are the 2.8-3.6 ppm regions of 1H NMR spectra following (A) irradiation of 10 in 35% D2O in
CD3CN; the resonances at ca. 2.9 and 3.4 ppm correspond to the vicinal methylene protons in N-deuteriobenzazepinedione (20-
N-d 1); (B) irradiation of 10 in 5% D2O in CD3CN; the resonance at ca. 2.9 ppm corresponds to the methylene protons (N-CH2) and
that at ca. 3.4 ppm to the methine proton in 20-N,r-d 2 showing that this solution contains a >5:1 ratio of 20-N,r-d 2: 20-N-d 1;
(C) irradiation of 10 in CD3CN; the resonances at ca. 3.05, 3.35, and 3.5 ppm correspond to the methine and diastereotopic methylene
protons in 20-TMS; (D) addition of D2O to C; the resonances corresponding to the methylene and methine protons of 20-N,r-d 2.
Application of this line of reasoning to understanding the
photochemical reactivity of the (silylalkyl)phthalimides
is only partially fruitful. For example, â-TMS radical
stabilization (expected to be in the range of 2.6-2.9 kcal/
mol)16 appears to be the reason why photolysis of (silyl-
ethyl)phthalimide 10 is unique in its generation of the
acetone adduct 21. This substance arises by excited-state
â-hydrogen abstraction which yields the stabilized dirad-
ical/azomethine ylide (if singlet) 34. Dipolar cycloaddi-
tion to 34 of acetone giving 21 (Scheme 5) has a strong
precedence gained in our earlier studies with (silylmeth-
yl)phthalimides.8
In order to fully understand how silicon substitution
in 10 (or 11) enhances the efficiency of benzazepinedione
20 (or amidol 28) formation, a significant question must
be resolved first; this concerns the mechanistic pathway-
(s) involved in transformation of 10 (or 11) to 20 (or 28).
Several experiments, were performed to gain information
about this issue. 1H NMR monitoring of the progress of
the photoreaction of 10, conducted in CD3CN under
rigorously anhydrous conditions, showed that the major
solution of 31 is reported to yield the methylbenza-
zepinedione 32 (29-39%) and the propenyl amidol 33
(18%).
The results outlined above show that a number of
features of (silylalkyl)phthalimide photochemistry are
quite different from those of their non-silicon analogs.
This is true in the case of the (silylethyl)phthalimide 10
which, in contrast to N-ethylphthalimide (24), undergoes
highly efficient photocyclization to produce benzazepinedi-
one 20 even under acetone triplet photosensitization
conditions. The inefficient photoreactivity of 24 is most
probably associated with a slow rate of γ-H atom abstrac-
tion from the primary center by the carbonyl of the
singlet or triplet excited phthalimide chromophore. This
process becomes more efficient when the γ-position is
methyl-substituted, as in the case of the propylphthal-
imide 31, owing to radical stabilization (i.e., BDE) effects.
(16) Davidson, J . M. T. Organometallics 1987, 6, 644.

3308 J . Org. Chem., Vol. 61, No. 10, 1996
Lee et al.
Sch em e 5
Sch em e 7
Sch em e 6
current results enable us to construct a reasonable
mechanistic framework to understand the unusual pho-
toreactivity of the (silylethyl)phthalimide 10 (as com-
pared to its non-silicon analogs 24 and 31) and the nature
of its photochemistry in solvent systems which differ in
their protic and silophilic character. Accordingly, we
suggest that the initial step in the sequence for photo-
reactions of 10 involves intramolecular SET from the
σC-Si bond to the phthalimide singlet (or triplet in the
case of acetone sensitization). This process finds prece-
dence in the work of Ohashi with silylalkanes and
cyanoarenes (see above). In aprotic-nonsilophilic sol-
vents (e.g. MeCN), proton transfer then occurs in the
zwitterionic diradical 37 from the acidic C-H (R to TMS)
to the oxy anionic center to produce the diradical 35
(Scheme 6) which serves as the precursor to the TMS-
substituted benzazepinedione 20-TMS. However, in
protic solvents (35% H2O-MeCN) where the basicity of
the oxy anion center is reduced by a H-bonding interac-
tion and where a silophile (H2O) is present in high
concentration, desilylation of 37 predominates (Scheme
7) leading to diradical 38 and eventually to direct
production of the benzazepinedione.
Observations which both support these mechanistic
proposals and demonstrate their synthetic consequences
have come from further studies with the (silylpropyl)-
phthalimide 11. As discussed above, irradiation of 11
in MeCN results in the production of a complex product
mixture. Formation of the benzazepinedione 27, amidol
28, and silylpropenyl amidols 29 and 30 in this solvent
system by competitive excited-state â- and γ-H-atom
abstraction reactions, parallels the behavior of the silyl-
ethyl analog 10. A remarkable change in the product
profile occurs when a protic-silophilic solvent system is
used for this reaction. Thus, preparative irradiation of
a 30% H2O-MeCN solution of 11 leads to exclusive
generation of the tricyclic amidol 28 in a 96% yield. 1H
NMR monitoring of this photoreaction (30% D2O-CD3-
CN) shows that 11 is cleanly converted to the O-D
analog of 28. Importantly, 28, formed under these
conditions, does not contain C-D incorporation, showing
that TMS group loss does not occur by protodesilylation
of a homolog of the R-silyl ketone 20-TMS. Clearly, the
primary product formed in this process is the R-silylben-
zazepinone, 20-TMS (See Figure 1, panel C and Scheme
6). Introduction of D2O into this photolysate leads to
rapid conversion of 20-TMS to the N,R-dideuteriobenza-
zepinedione, 20-N,r-d 2 (Figure 1, panel D). These ob-
servations demonstrate that the major (if not exclusive)
pathway followed in photoconversion of 10 to 20 involves
initial formation of the diradical intermediate 35 by a
γ-hydrogen-atom-transfer process (see below) followed by
sequential cyclization, producing the transient azetidinol
36, and amidol ring opening yielding 20-TMS (Scheme
6). As an R-silyl ketone, 20-TMS undergoes rapid
protonolysis of the C-Si bond (with adventitious water
1
to form 20 in the H NMR experiment) as indicated by
production of 20-N,r-d 2 when 20-TMS is exposed to D2O.
Another observation which provides additional infor-
mation about the source of the unique reactivity of the
N-(silylethyl)phthalimide 10 has come from a study of
the photoreaction of this substance in aqueous MeCN.
Specifically, 1H NMR analysis (Figure 1, panel A) shows
that irradiation of 10 in 35% D2O-CD3CN efficiently
produces the N-deuteriobenzazepinedione 20-N-d 1 exclu-
sively. Thus, in a protic and highly silophilic solvent
system 10 is transformed to 20 by a mechanism which
does not involve the intermediacy of the silicon-contain-
ing benzazepinedione 20-TMS. Instead, 20 appears to
form directly from the excited state of 10 via a pathway
most likely involving direct production of diradical 38
through desilylation of the zwitterionic diradical 37
(Scheme 7).
The effect of the protic-silophilic solvent is reminiscent
of similar observations made in our earlier studies of the
photoreactivity of silylamino enones.17 The previous and
(17) (a) Hasegawa, E.; Xu, W.; Mariano, P. S.; Yoon, U. C.; Kim, S.
U. J . Am. Chem. Soc. 1988, 109, 8089. (b) Xu, W.;Mariano, P. S. J .
Am. Chem. Soc. 1991, 113, 1431.

H-Atom Abstraction and Silyl-Transfer Photoreactions
J . Org. Chem., Vol. 61, No. 10, 1996 3309
efficient production of 28 by irradiation of 11 in 30%
H2O-MeCN is a consequence of selective desilylation of
an intermediate zwitterionic diradical formed by photo-
induced SET. In addition, this mechanistic alteration
promoted by a change in the solvent system transforms
an unselective process into one that is selective has
preparative potential.
Silyla m id o Keton e P h otoch em istr y. The general-
ity of the mechanistic conclusions outlined above is also
demonstrated by the photochemistry of the R-silylamido
ketones 12 and 13. Both of these substances contain an
n-electron donor site within the alkyl chain connecting
the σC-Si bond and phenone groupings. Moreover, cation
radicals derived by SET oxidation of the R-silylamido
functions in 12 and 13 are delocalized (i.e., they have two
contributing resonance representations 39). As a con-
sequence of this feature, the oxidation potentials of
R-silylamides are lower than those of simple alkylsilane
analogs. Therefore, it is expected that SET pathways will
dominate the photochemistry of these substances.
Sch em e 8
8). The diradicals 48 formed in this fashion undergo
selective cyclization rather than fragmentation, a char-
acteristic observed previously in photochemical studies
of amido ketones.18 Hydrogen migration (yielding 42 or
46) and â-cleavage photoprocesses (yielding the respec-
tive acylarenes and 43) occur to a lesser extent in the
excited-state chemistry of these substances.
Another interesting observation is that the phenyl and
2-naphthyl ketones 12 and 13 react with near equal
quantum efficiencies (0.40 and 0.33, respectively). This
is an expected characteristic of reaction by SET pathways
where, unlike H-atom abstractions, only the redox prop-
erties (and not electronic configurations or multiplicities)
of the excited aryl ketone chromophores govern reaction
efficiencies.
Irradiation (λ > 280 nm) of an MeCN solution of the
phenone 12 followed by alumina chromatography results
in the isolation of the azetidines 40 (22%), 41 (13%), and
42 (9%). 1H NMR monitoring of this photoreaction shows
that the crude photolysate (CD3CN) contains azetidines
40 and 42 only (29% and 18%, respectively) along with
acetophenone (6%) and benzyl N-(trimethylsilyl)carbam-
ate (43, 6%). In a similar manner, the 2-naphthyl ketone
Silyla lk yl Keton e P h otoch em istr y. Both the (si-
lylalkyl)phthalimides and silylamido ketones, whose
photochemical properties are described above, contain
structural features which encourage the operation of
excited-state SET processes. Accordingly, the excited
phthalimide function is a good acceptor and the silyla-
mido grouping is a good SET donor. Simple silylalkyl
ketones such as the phenone 14 and 2-naphthone 15, at
first sight seem to lack these driving forces for excited-
state SET, and therefore, they would be expected to
mimic simple aryl ketones in their photochemical reac-
tivity.
In line with this expectation, both 1419 and 15 react
cleanly when irradiated in MeCN to produce products
resulting from the operation of Norrish Type II (acylare-
nes and vinyl trimethylsilane) and/or â-cleavage (vinyl
trimethylsilane and diketones) pathways. The results of
these photoreactions are summarized in Scheme 9.
13 reacts upon irradiation to give azetidines 44-46 (6%,
1
15%, and 1% isolated, 37%, 0%, and 5% by H NMR),
2-acetonaphthone (14%), and carbamate 43 (5%).
The major primary products generated in photoreac-
tions of the phenyl and 2-naphthyl silylamido ketones
12 and 13 are the siloxyazetidines 40 and 44, respec-
tively. These substances are produced with near equal
efficiencies (see below) by routes involving intramolecular
silyl transfer in the intermediate zwitterionic diradicals
47, themselves being formed by excited-state SET (Scheme
(18) Gold, E. H. J . Am. Chem. Soc. 1971, 93, 2793. Allworth, K. L.;
El-Hamamy, A. A.; Hesabi, M. M.; Hill, J . J . Chem. Soc., Perkin Trans.
1 1980, 1671.
(19) The results of the current study with 14 match those found
earlier by Kuivila (ref 14).

3310 J . Org. Chem., Vol. 61, No. 10, 1996
Lee et al.
Sch em e 9
this analysis is not the silyl enol ether which has
different spectroscopic properties and solution lifetimes.
Sch em e 10
Thus, in the case of 16 and most probably in photore-
actions of the related ketones 14 and 15, the major
reaction pathway in MeCN is γ-hydrogen atom abstrac-
tion leading to formation of the 1,4-diradical 52 (Scheme
10). Bond scission then generates the enol and the
vinylsilane. As anticipated for operation of a H-atom
abstraction route, the quantum efficiencies for photore-
actions of the phenyl and 2-naphthyl ketones differ
greatly; i.e., 0.90 (MeCN) for reaction of 14 with a lowest
energy n-π* triplet and 0.01 (MeCN) for reaction of 15
with a lowest π-π* triplet state.21
An observation, which suggests that another mecha-
nistic route can become competitive with H-atom ab-
straction in the excited state chemistry of the silylalkyl
ketones, relates to the effect of protic/silophilic solvents
on the nature of the products produced. As indicated
1
above, H NMR analysis shows that irradiation of 16 in
CD3CN leads to production of the enol 53 (Ar ) p-CNC6H4)
and vinylsilane in near equal amounts. In contrast,
photolysis of 16 in CD3OD, monitored by 1H NMR, again
gives enol 53 and the vinylsilane but this time in a ratio
of 1.6:1. In a similar manner, photoreaction of the phenyl
ketone 14 in CD3OD gives acetophenone and vinyltri-
methylsilane in a 1.8:1 ratio as compared to the 0.8:1
ratio of these products when 14 is irradiated in CD3CN.
A full interpretation of the latter results is difficult to
formulate. However, the observations suggest that two
mechanism are responsible for generation of the acyl-
arene products in the photoreactions of the aryl ketone
14-16. The major pathway in MeCN involves initial
γ-hydrogen abstraction by the carbonyl n-π* triplet and
generates the acylarene and vinylsilane products in equal
amounts (Scheme 10). Another route operates competi-
tively for photoreactions of 14-16 in the protic-silophilic
solvent MeOH and it appears to lead to generation of the
acylarenes but not vinyltrimethylsilane. A reasonable
proposal to explain this outcome would invoke methanol-
induced desilylation of CT complexes or even a zwitte-
rionic diradical 54 formed by interaction of the σC-Si and
excited carbonyl moieties (Scheme 10). This process
would produce the non-silicon-containing diradical 55,
the precursor of the acylarenes and ethylene. Clearly,
if this proposal were to be correct, a close link would exist
between the excited-state reaction profiles of the (silyl-
In the absence of additional information, it is difficult
to determine what fraction of the products formed in the
photoreactions of 14 and 15 derive from the Norrish Type
II and â-cleavage processes. As can be seen by viewing
Scheme 10, the â-cleavage reaction could yield all three
of the observed products, the acylarenes and vinyltri-
methylsilane arising by disproportionation in the initially
formed radical pair and the diketone by out-of-cage
combination. However, a more careful study of the
photoreaction of the p-cyano analog 16 provides impor-
tant information on this issue. For example, preparative
irradiation of 16 in MeCN leads to production of the
acylarene 49 (91%), vinyltrimethylsilane (92%), 1,4-
diketone 50 (1%), and cyclobutanol 51 (7%). 1H NMR
monitoring of the photoreaction of 16 in anhydrous CD3-
CN shows that the enol 53 (Scheme 10, Ar ) p-CN-C6H4)
is the major primary product (terminal vinyl protons at
4.45 and 4.80 ppm) formed simultaneously with and in
near equal amounts to vinyltrimethylsilane. The stable
(due to the p-CN substituent)20 enol 53 tautomerizes over
a 12 h period at 25 °C to generate the ketone 49. It is
important to note that the intermediate 53 detected by
(21) See: Cohen, S. G.; Davis, G. A.; Clark, W. D. K. J . Am. Chem.
Soc. 1972, 94, 869 and references therein.
(20) Kresge, A. J . Pure Appl. Chem. 1991, 63, 213.

H-Atom Abstraction and Silyl-Transfer Photoreactions
J . Org. Chem., Vol. 61, No. 10, 1996 3311
1710; LRMS m/z 247 (M, 25), 246 (100), 232 (65), 204 (66),
160 (27), 130 (43); HRMS m/z 247.1037 (C13H17NO2Si requires
247.1029).
alkyl)phthalimide, silylamido ketone, and silylalkyl ke-
tone systems.
P r ep a r a tion of N-[3-(Tr im eth ylsilyl)p r op yl]p h th a lim -
id e (11). To a solution of 3-(trimethylsilyl)-1-propanol (5.0 g,
38 mmol) and Et3N (4.1 g, 41 mmol) in 40 mL of Et2O at 0 °C
was added a solution of MsCl (3.0 mL, 39 mmol) in 20 mL of
ether dropwise. The resulting mixture was stirred at 25 °C
for 18 h and filtered. The filtrate was concentrated in vacuo
giving a residue which was vacuum distilled to give 8.0 g (ca.
100%) of the mesylate derivative (125 °C, 3 mm): 1H NMR
-0.04 (s, 9 H, SiMe3), 0.48 (m, 2 H, CH2Si), 1.63 (q, J ) 7.2
Hz, CH2), 2.96 (s, 3 H, S-Me), 4.12 (t, J ) 7.2 Hz, 2 H, CH2O);
13C NMR -2.0 (SiMe3), 11.4 (CH2Si), 23.8 (CH2), 37.2 (SMe),
72.5 (OCH2); IR 1352, 1170.
A solution of NaI (23 g, 0.15 mol) and the mesylate (8.0 g,
0.038 mol) in 40 mL of acetone was stirred at reflux for 18 h
and then extracted with pentane. The pentane layer was
concentrated in vacuo and distilled to give 9.1 g (99%) of the
corresponding iodide (59 °C, 3 mm): 1H NMR -0.04 (s, 9 H,
SiMe3), 0.55 (m, 2 H, CH2Si), 1.78 (m, 2 H, CH2), 3.14 (t, 2 H,
J ) 7.3 Hz, CH2I); 13C NMR -1.7 (SiMe3), 11.1 (CH2Si), 18.7
(CH2), 28.9 (CH2I).
Su m m a r y
The studies outlined above have provided a broad
overview of the types of photochemical processes that
occur in substances which possess tethered silylalkane
or amide and aryl ketone or phthalimide groups. The
accumulated results demonstrate that classical Norrish
Type II or Yang photoreactivity, initiated by carbonyl
excited-state H-atom abstraction, dominates in these
systems when photoreactions occur in less polar, aprotic,
and nonsilophilic solvents. However, clear evidence has
been gathered to show that CT or SET interactions
between excited carbonyl and ground state σC-Si group-
ings doe occur and that in silophilic solvents this can lead
to cleavage of the C-Si bond and to activation of unique
excited -state reaction pathways. Finally, the observa-
tion that silicon substitution in alkylphthalimides en-
hances the efficiencies of their photocyclization reactions
brings synthetic significance to the results of this inves-
tigation.
A solution of 1.74 g (7.2 mmol) of the iodide and 1.30 g (7.7
mmol) of sodium phthalimide in DMF was subjected to the
reaction work up and purification conditions described for
preparation of 10 above. This gave 1.76 g (96%) of the
phthalimide 11 (mp 60-61 °C): 1H NMR -0.04 (s, 9 H, SiMe3),
0.50 (m, 2 H, CH2Si), 1.65 (quintet, J ) 7.4 Hz, 2 H, CH2),
Exp er im en ta l Section
Gen er a l. 1H NMR and 13C NMR spectra were recorded
using CDCl3 solutions and chemical shifts are reported in ppm
relative to CHCl3 (δ 7.24 ppm for 1H and δ 77.0 ppm for 13C)
which was used as a chemical shift internal standard for
samples in CDCl3; 13C NMR resonance assignments were aided
by the use of the DEPT technique to determine numbers of
attached hydrogens. IR spectra vibrational frequencies are
expressed in wave numbers (cm-1). Column chromatography
was performed with either Merck-EM type 60 (230-400 mesh)
or Alcoa type F-20 alumina (neutral, 80-200 mesh) absor-
bants. Preparative TLC was performed on 20 × 20 cm plates
coated with Merck-EM type 60 GF-254 silica gel. Gas chro-
matographic analyses were conducted on a chromatograph
with a flame ionization detector. Mass spectra were recorded
by using electron impact ionization unless specified as chemi-
cal ionization by CI. All reactions were run under a dry N2
atmosphere unless otherwise noted. Organic extracts obtained
following workup of reaction mixtures were dried over anhy-
drous Na2SO4 or MgSO4. All compounds prepared in this
study were oils and were judged by NMR to be >90% pure
unless otherwise noted.
Preparative photochemical reactions were conducted with
an apparatus consisting of a 450 W Hanovia medium-pressure
mercury lamp surrounded by a glass filter (for wavelength
band selection) immersed in the photolysis solution. The
photolysis solutions were purged with N2 both before and
during irradiation. The progress of each preparative photo-
chemical reaction was monitored by UV absorption spectrom-
etry, gas chromatography, TLC, and/or H NMR spectroscopy.
Sealed NMR tubes were devoided of air by using N2 purging
before irradiations.
3.64 (t, J ) 7.4 Hz, 2 H, CH2N), 7.67-7.84 (m, 4 H, arom); 13
C
NMR -1.8 (SiMe3), 13.8 (CH2Si), 23.6 (CH2), 41.1 (N-CH2),
123.1, 132.2, 133.8 (arom), 168.5 (CdO); IR 1711; LRMS m/z
261 (M, 16); 246 (33), 232 (49), 204 (33), 131 (77), 130 (17),
119 (100), 100 (14); HRMS m/z 261.1185 (C14H19NO2Si requires
261.1186).
P r ep a r a tion of r-Silyla m id oa cetop h en on e 12. To a
solution of 0.76 g (2.7 mmol) of the known13 amidoaldehyde
17 in 20 mL of anhydrous THF was added a THF solution of
1.4 mL (4.1 mmol) of phenylmagnesium bromide (Aldrich) at
-78 °C. The resulting solution was stirred for 3 h at -15 °C,
quenched by addition of saturated aqueous NH4Cl and ex-
tracted with ether. The ethereal extracts were dried over Na2-
SO4 and then concentrated in vacuo to give a residue which
was subjected to Florisil column chromatography (20% Et2O/
cyclohexane) to yield 0.76 g (2.1 mmol, 79%) of the amido
alcohol 18: 1H NMR -0.02 (broad, 9H, SiCH3), 2.71-2.88
(broad, SiCH2), 3.20-3.73 (broad, 2 H, H-2), 4.06 (broad, 1 H,
H-1), 5.08 (s, 2 H, benzylic), 7.30 broad, 10 H, aromatic); 13C
NMR -1.60 (SiCH3), 40.6 (SiCH2), 58.0 (C-2), 67.5 (benzylic),
73.5 (C-1), 125.8, 127.9,128.1, 128.2, 128.5, 136.5 and 142.3
(aromatic), 158.0 (NCO); IR 3560-3250, 3020, 2975, 2895,
1600, 1520, 1475, 1420, 1155, 1095, 925; LRMS m/z 358 (M+
+ 1, 26), 341, (5), 340 (19), 280 (16), 266 (11), 250 (26), 206
(25), 116 (9), 104 (17), 91 (100), 73 (25); HRMS m/z 358.1846
(M+ + 1, C20H28NO3Si requires 358.1839).
The amido alcohol 18 (0.29 g, 8.2 × 10-1 mmol) was oxidized
by the procedure of Swern using 0.18 mL (2.0 mmol) of oxalyl
chloride and 0.28 mL (4.0 mmol) of DMSO and 2 mL of
triethylamine. Concentration gave amidophenone 12 (0.29 g,
8.2 × 10-1 mmol, >98%) which was used without further
purification. 1H NMR 0.02 and 0.08 (s, 9 H, SiCH3), 2.89 and
2.93 (s, 2 H, SiCH2), 4.65 and 4.74 (s, 2 H, H-2), 5.08 and 5.16
(s, 2 H, benzylic), 7.21-7.94 (m, 10 H, aromatic); 13C NMR
-1.69 (SiCH3), 39.9 and 41.1 (SiCH2), 55.9 (C-2), 67.4 (ben-
zylic), 127.8, 128.3, 128.7, 133.3, 135.6 and 136.8 (aromatic),
156.8 (NCO), 194.5 (C-1); IR 3070, 3020, 2980, 2960, 2900,
1700, 1450, 1405, 1220, 1110, 860; LRMS m/z 355 (M+, 0.08),
340 (2), 310 (1), 264 (4), 248 (2), 220 (7), 206 (4), 192 (10), 177
(4), 105 (9), 91 (100), 73 (25); HRMS m/z 356.1674 (M+ + 1,
C20H26NO3Si requires 356.1682).
1
3-(Trimethylsilyl)-1-propanol, 2-(trimethysilyl)-1-ethanol,
and 4-(trimethylsilyl)butyronitrile were purchased from Pe-
trarch, and sodium phthalimide and 4-cyanobenzoic acid were
purchased from Aldrich.
P r ep a r a tion of N-[2-(Tr im eth ylsilyl)eth yl]p h th a lim id e
(10). A solution of 1.50 g (11 mmol) of 2-(chloroethyl)-
trimethylsilane (prepared from the corresponding alcohol by
reaction with SOCl2) and 2.03 g (12 mmol) of sodium phthal-
imide in 20 mL of DMF was stirred at 85 °C for 7 h and
concentrated in vacuo. The residue was diluted with Et2O,
filtered, and then subjected to column chromatography (silica,
1:4 EtOAc-hexane) to give 1.51 g (56%) of the phthalimide
10 (mp 64-65 °C): 1H NMR 0.05 (s, 9 H, SiMe3), 0.99 (t, J )
7.3 Hz, 2 H, CH2Si), 3.70 (t, J ) 7.3 Hz, 2 H, CH2N), 7.64-
7.83 (m, 4 H, arom); 13C NMR -1.8 (SiMe3), 17.1 (CH2Si), 34.4
(CH2N), 123.0, 132.3, 132.3, 133.7 (arom), 168.2 (CdO); IR
P r ep a r a tion of r-Silyla m id o-2-a ceton a p h th on e 13. To
a solution of the known amido aldehyde 17 (2.79 g, 0.010 mol)
in 20 mL of anhydrous THF at -78 °C was added a solution
of 0.013 mol of 2-naphthylmagnesium bromide in THF (15
mL). The resulting solution was stirred at 25 °C for 24 h,
quenched by adding saturated aqueous NH4Cl (6 mL), and

3312 J . Org. Chem., Vol. 61, No. 10, 1996
Lee et al.
extracted with ether. The ethereal extracts were dried and
concentrated in vacuo to give 4.3 g (100%) of the naphthyl
alcohol 19 which was used without further purification. 1H
NMR -0.04 (br s, 9 H, SiCH3), 2.77 (br s, 2 H, SiCH2), 2.86
(br s, 1 H, OH), 3.30-3.70 (m, 2 H, H-2), 4.20 (br s, 1 H, H-1),
5.15 (br s, 2 H, PhCH2), 7.06-7.83 (m, 12 H, aromatic).
based on 31% conversion) of the known15 benzazepinedione 20
(mp 161-162 °C).
Ir r a d ia tion in Aceton e. A solution of 10 (500 mg, 2.02
mmol) in 200 mL of acetone under N2 was irradiated with
Vycor-filtered light for 24 h (51% conversion of 10). Chroma-
tography under the conditions described above gave 74 mg
(41% based on recovered 10) of benzazepinedione 20 and 22
mg (7%) of the acetone adduct 21: 1H NMR 0.11 (s, 9 H,
SiMe3), 0.68 (s, 3 H, Me), 1.24 (dd, J ) 14.0, 6.8 Hz, 1 H, CH2-
Si), 1.33 (dd, J ) 14.0, 6.8 Hz, 1 H, CH2Si), 1.53 (s, 3 H, Me),
2.63 (s, 1 H, OH), 5.36 (t, J ) 6.8 Hz, 1 H, CHN), 7.43-7.73
(m, 4 H, arom); 13C NMR -1.0 (SiMe3), 21.9 (Me), 22.9 (Me),
27.2 (CH2Si), 82.1 (CMe2), 84.9 (N-C), 96.3 (CO), 122.0, 124.0,
130.3, 133.0, 133.3, 144.3 (arom), 170.4 (CdO); IR 3450, 1695;
LRMS (CI) m/z 306 (M + 1, 17), 290 (20), 262 (15), 247 (73),
246 (100), 218 (74), 190 (40); HRMS (CI) m/z M + 1, 306.1525
(C16H24NO3Si requires 306.1526).
Ir r a d ia tion in Aceton e-Meth a n ol. A solution of 10 (500
mg, 2.02 mmol) in 200 mL of acetone containing 10% CH3OH
was irradiated with Vycor-filtered light under N2 purging for
7 h (100% conversion of 10). The residue obtained by
concentration of the photolysate was subjected to column
chromatography (silica, EtOAc) to give 80 mg (16%) of the
reduction product 22 and 425 mg (75%) of the addition product
23.
The alcohol 19 (4.0 g, 9.8 mmol) was oxidized by the
procedure of Swern using 2.14 mL (0.02 mol) of oxalyl chloride
and 2.79 mL (0.04 mol) of DMSO. The reaction was quenched
by adding 6.85 mL of triethylamine, and the mixture was
extracted with CH2Cl2. The CH2Cl2 extracts were washed with
water and concentrated in vacuo to give a residue which was
subjected to column chromatography (Florisil, 20% ether/
hexane) to yield 1.79 g (45%) of the amido naphthone 13: 1H
NMR (rotamer mixture) 0.05 and 0.13 (s, 9 H, SiCH3), 2.95
and 2.98 (s, 2 H, SiCH2), 4.81 and 4.86 (s, 2 H, H-2), 5.12 and
5.19 (s, 2 H, PhCH2) 7.27-8.08 (m, 11 H, aromatic), 8.39 and
8.49 (s, 1 H, H-1-naphthyl); 13C NMR (a 1:1 rotamer mixture)
-1.7 and -1.6 (SiCH3), 39.8 and 41.1 (SiCH2), 56.0 (C-2), 67.3
and 67.6 (PhCH2), 123.5, 123.6, 126.9, 127.8, 128.0, 128.2,
128.4, 128.7, 129.4, and 129.6 (aromatic, CH), 132.5, 132.6,
135.8, and 136.7 (aromatic, ipso), 156.5 (NCdO), 194.7 (C-1);
IR 3062, 2953, 1700, 1457, 1248, 856; LRMS (CI) m/z 406 (M
+ 1,20), 390 (23), 360 (13), 314 (40), 298 (11), 270 (40), 242
(100), 241 (29), 227 (33), 206 (40), 155 (45), 141 (24), 127 (22);
HRMS (CI) m/z 406.1847 (M + 1, C24H28NO3Si requires
406.1838).
22: 1H NMR -0.01 (s, 9 H, TMS), 0.68-0.77 (m, 1 H, CH2-
TMS), 0.84-0.93 (m, 1 H, CH2TMS), 3.03-3.12 (m, 1 H,
NCH2), 3.28-3.37 (m, 1 H, NCH2), 3.81 (d, J ) 12.0 Hz, 1 H,
NCHOH), 5.73 (d, J ) 12.0 Hz, 1 H, OH), 7.37-7.61 (m, 4 H,
aromatic); 13C NMR -1.7 (TMS), 16.3 (CH2TMS), 35.1 (NCH2),
80.9 (NCH), 123.1, 123.3, 129.6, 131.8, 132.0, 144.0 (aromatic),
166.9 (CdO); IR 3650-3200, 1698; LRMS m/z 249 (M, 7), 234
(21), 206 (18), 133 (23), 75 (34), 73 (43), HRMS m/z 249.1185
(C13H19NO2Si requires 249.1186).
P r ep a r a tion of 4-(Tr im eth ylsilyl)-2-bu tyr on a p h th on e
(15). To a solution of (3-cyanopropyl)trimethylsilane (1.90 g,
0.014 mol) in 30 mL of anhydrous THF was added 0.15 mol of
2-naphthylmagnesium bromide in 25 mL of THF dropwise at
25 °C over a 0.5 h period. The mixture was then stirred at
reflux for 3 days, quenched by addition of saturated aqueous
NH4Cl, and extracted with ether. The ethereal extracts were
dried and concentrated in vacuo to give a residue which was
subjected to column chromatography (silica gel, 20% ether/
hexane) to yield 1.06 g (28%) of the naphthyl ketone 15: 1H
NMR 0.00 (s, 9 H, SiCH3), 0.56-0.65 (m, 2 H, H-4), 1.80 (m,
2 H, H-3), 3.11 (t, J ) 7.3 Hz, 2 H, H-2), 7.50-8.04 and 8.45
(m, 7 H, aromatic); 13C NMR -2.0 (SiCH3), 14.0 (C-4), 16.6
(C-3), 42.2 (C-2), 123.8, 126.6, 127.6, 128.2, 128.3, 129.4, and
129.5 (aromatic, CH), 132.5, 134.4, and 135.4 (aromatic, ipso),
200.3 (C-1); IR 3059, 2951, 1682, 1248, 862, 837, 749; LRMS
(CI) m/z 271 (M + 1, 32), 270 (39), 255 (100), 242 (56), 241
(47), 170 (34), 165 (8), 155 (67), 127 (30), 73 (49); HRMS m/z
270.1429 (C17H22OSi requires 270.1440).
1
23: Mp 138-139°C; H NMR -0.03 (s, 9 H, TMS), 0.64-
0.73 (m, 1 H, CH2TMS), 0.88-0.97 (m, 1 H, CH2TMS), 2.14 (t,
J ) 6.8 Hz, OH), 2.73-2.82 (m, 1 H, NCH2), 3.04-3.12 (m, 1
H, NCH2), 3.74 (dd, J ) 11.6, 6.8 Hz, 1 H, CH2O), 3.92 (dd, J
) 11.6, 6.8 Hz, 1 H, CH2O), 4.68 (s, 1H, OH), 7.38-7.63 (m, 4
H, aromatic); 13C NMR -1.8 (TMS), 17.6 (CH2TMS), 34.9
(NCH2), 65.4 (CH2O), 89.9 (COH), 122.6, 123.1, 129.7, 131.4,
132.2, 145.5 (aromatic), 167.8 (CdO); IR 3700-3300, 1695;
LRMS (CI) m/z 279 (m, 0.4), 264 (20), 248 (42), 232 (100), 224
(57), 204 (84), 160 (31), 130 (33); HRMS m/z 279.1290 (C14H21
-
NO3Si requires 279.1291).
Sea led -Tu be Ir r a d ia tion . A solution of 5 mg (0.021 mmol)
of 10 in 0.5 mL of CD3CN was irradiated for 2 h in a degassed
(freeze-thaw) sealed NMR tube. NMR analysis of the pho-
tolysate indicated that it contained a mixture of the benza-
zepinedione 20 and its R-silyl analog 20-TMS in a 1:6 ratio.
Partial spectroscopic data for 20-TMS: 1H NMR (CD3CN) 3.02
(dd, J ) 12.0, 4.0 Hz, 1 H, CHSi), 3.33 (ddd, J ) 15.0, 7.0, 4.0
Hz, 1 H, NCH2), 3.54 (ddd, J ) 15.0, 12. 0, 7.0 Hz, 1 H, CH2N);
13C NMR 39.5 (NCH2), 54.3 (CHSi).
P h otoch em istr y of N-Eth ylp h th a lim id e (24). A solution
of phthalimide 24 (350 mg, 2.0 mmol) in 200 mL of acetone
was irradiated with Vycor-filtered light with N2 purging for
20 h (51% conversion of 24). The residue obtained by
concentration in vacuo was subjected to column chromatog-
raphy (silica, EtOAc-CHCl3) to give 15 mg (8%) of 20, 68 mg
(29%) of 18, and 5 mg (3%) of 26.
P r ep a r a t ion of [4-(Tr im et h ylsilyl)b u t yr yl]-p -cya n -
op h en on e (16). A solution of 4-cyanobenzoic acid (2.0 g, 0.014
mol) in thionyl chloride (40 mL) was stirred at reflux for 4 h.
Solvent was evaporated in vacuo. The solid residue, 4-cy-
anobenzoyl chloride (mp 66-67 °C), was then dissolved in 20
mL anhydrous THF. [3-(Trimethylsilyl)-1-propyl]magnesium
chloride (0.027 mol in 14 mL of THF) was added and the
resulting mixture was stirred at -78 °C for 1.5 h. The reaction
was quenched by adding 3 N HCl and the mixture extracted
with ether. The ethereal extracts were washed with 0.5 N
KOH, dried, and concentrated in vacuo to give a residue which
was subjected to column chromatography (silica gel, 10% ether/
hexane) to yield 1.0 g (30%) of the cyanophenone 16: 1H NMR
-0.02 (s, 9 H, SiCH3), 0.49-0.58 (m, 2 H, H-4), 1.71 (m, 2 H,
H-2), 2.98 (t, J ) 7.2 Hz, 2 H, H-3), 7.74 and 8.01(AB q, J )
8.5 Hz, 4 H, aromatic); 13C NMR -1.9 (SiCH3), 16.5 (C-4), 18.7
(C-3), 42.4 (C-2), 116.1 (CN), 128.3 and 132.2 (aromatic, CH),
117.8 and 140.0 (aromatic, ipso), 198.9 (C-1); IR 3068, 2953,
2230, 1693, 1404, 1248, 1215, 838, 750; LRMS m/z 245 (M, 5),
231 (14), 230 (68), 218 (15), 217 (71), 216 (50), 203 (28), 202
(100), 130 (43); HRMS m/z 245.1237 (C14H19NOSi requires
245.1236).
25: 1H NMR 1.22 (t, J ) 6.7 Hz, 3 H, CH3), 2.15 (s, 3 H,
COCH3), 2.96 (d, J ) 16.6 Hz, 1 H, CH2-CO), 3.21 (d, J ) 16.6
Hz, 1 H, CH2-CO), 3.25-3.36 (m, 1 H, CH2), 3.48-3.59 (m, 1
H, CH2), 5.05 (s, 1 H, OH), 7.39-7.69 (m, 4 H, aromatic); 13C
NMR 14.5 (CH3), 31.5 (COCH3), 33.8 (CH2CO), 49.1 (CH2), 88.5
(COH), 121.6, 123.3, 129.6, 131.0, 132.2, 146.7 (aromatic),
166.9 (NCdO), 207.8 (CdO); IR 3650-3200, 1695; LRMS m/z
233 (M, 6), 232 (8), 216 (6), 191 (7), 190 (12), 177 (20), 176
(100), 175 (35), 172 (39), 160 (68), 148 (30), 147 (25); HRMS
m/z 233.1052 (C13H15NO3 requires 233.1053).
P h otoch em istr y of N-[3-(Tr im eth ylsilyl)pr opyl]ph th al-
im id e (11). In MeCN. Irradiation of a MeCN (200 mL)
solution containing the (silylpropyl)phthalimide 11 (550 mg,
2.10 mmol) was conducted by using Vycor-filtered light for 6
h (55% conversion of 11). Chromatography (silica, 1:4 EtOAc-
P h otoch em istr y of N-[2-(Tr im eth ylsilyl)eth yl]p h th a l-
im id e (10). Ir r a d ia tion in MeCN. A solution of 500 mg
(2.02 mmol) of the (silylethyl)phthalimide 10 in 200 mL of
MeCN under N2 was irradiated with Vycor-filtered light for
7.5 h (31% conversion of 10). Chromatography (silica, EtOAc)
of the residue obtained by concentration of the photolysate
gave 75 mg (68% based on 31% conversion) or 389 mg (66%

H-Atom Abstraction and Silyl-Transfer Photoreactions
J . Org. Chem., Vol. 61, No. 10, 1996 3313
CH2Cl2) of the residue obtained by concentration of the
photolysate gave 85 mg (28%) of 27 (mp 54-55 °C), 46 mg
(21%) of 28 (mp 123-125 °C); 34 mg (11%) of 29 (mp 84-85
°C), and 20 mg (6%) of 30 (mp 70-71 °C).
41: 1H NMR 2.60 (br s, 1 H, OH), 4.23 and 4.35 (AB q, J )
9.5 Hz, 4 H, H-2, and H-4), 5.11 (s, 2 H, PhCH2), 7.28-7.49
(m, 10 H, aromatic); 13C NMR 64.4 (C-2 and C-4), 66.9 (PhCH2),
71.9 (C-3), 124.5, 128.0, 128.1, 128.1, 128.5, and 128.8 (aro-
matic, CH), 136.5 and 142.8 (aromatic, ipso), 156.6 (NCdO);
IR 3500-3400, 1685, 1451, 1357, 757, 698; LRMS (CI) m/z 284
(M + 1, 10), 224 (5), 220 (7), 178 (15), 148 (23), 134 (31), 120
(90), 105 (100); HRMS m/z 283.1212 (C17H17NO3 requires
283.1208).
27: 1H NMR 0.07 (s, 9 H, SiMe3), 0.72 (dd, J ) 14.9, 9.2
Hz, 1 H, CH2Si), 1.03 (dd, J ) 14.9, 5.8 Hz, 1 H, CH2Si), 2.96
(m, 1 H, CH-), 3.33 (m, 1 H, NCH2), 3.44 (m, 1 H, NCH2),
6.84 (s, 1 H, NH), 7.5-7.9 (m, 4 H, arom); 13C NMR -0.8
(SiMe3), 18.0 (CH2Si), 44.3 (CH2N), 52.1 (CH), 128.4, 129.7,
131.2, 132.0, 132.1, 136.8 (arom), 171.1, 207.0 (CdO); IR 1678;
LRMS m/z 262 (M + 1, 5), 229 (5), 217 (20), 195 (21), 160 (27);
HRMS (CI) m/z 262.1263 (C14N20NO2Si requires 262.1264).
28: 1H NMR 1.45 (m, 1 H), 2.24 (m, 2 H), 2.58 (m, 1 H),
3.23 (m, 1 H, CHN), 3.49 (m, 1 H, CHN), 3.88 (s, 1 H, OH),
7.32-7.53 (m, 4 H, arom); 13C NMR 27.6 (CH2), 34.6 (CH2),
41.2 (NCH2), 96.4 (quart. C), 122.5, 123.4, 129.5, 131.6, 132.6,
147.3 (arom), 170.1 (CdO); IR 3300 (br), 1684; LRMS m/z 189
(M, 100), 174 (14), 172 (67), 170 (38), 161 (80); HRMS m/z
189.0790 (C11H11NO2 requires 189.0790).
42: 1H NMR 0.17 (br s, 9 H, SiCH3), 4.17 (d, J ) 9.8 Hz, 1
H, H-4), 4.23 (s, 1 H, H-2), 4.56 (d, J ) 9.8 Hz, 1 H, H-4), 5.09
(s, 2 H, PhCH2), 7.25-7.45 (m, 10 H, aromatic); 13C NMR -1.7
(SiCH3), 64.9 (C-4), 66.8 (PhCH2), 69.3 (C-2), 75.1 (C-3), 124.5,
127.8, 128.0, 128.2, 128.4, and 128.8 (aromatic, CH), 136.7 and
144.7 (aromatic, ipso), 156.5 (NCdO); IR 3500-3400, 3030,
2951, 1684, 845, 698; LRMS m/z 355 (M, 0.65), 340 (12), 264
(10), 236 (30), 220 (100), 206 (25), 192 (99.98), 177 (34), 130
(21), 120 (30), 105 (35); HRMS m/z 355.1599 (C20H25NO3Si
requires 355.1604).
43: 1H NMR 0.04 (s, 9 H, SiCH3), 2.66 (d, J ) 5.5 Hz, 2 H,
SiCH2), 4.51 (br s, 1 H, NH), 5.08 (s, 2 H, PhCH2), 7.34 (m, 5
H, aromatic); 13C NMR -2.87 (SiCH3), 26.9 (SiCH2), 66.8
(PhCH2), 128.1, 128.2, and 128.5 (aromatic, CH), 136.7 (aro-
matic, ipso), 157.3 (NCdO); IR 3400-3300, 3034, 2955, 1700,
1540, 1273, 858; LRMS m/z 237 (M, 0.18), 236 (0.92), 220 (23),
178 (7), 146 (13), 102 (48), 91 (100), 73 (96), 59 (5); HRMS m/z
237.1162 (C12H19NO2Si requires 237.1185).
29: 1H NMR -0.01 (s, 9 H, SiMe3), 1.62 (s, 1 H, OH), 3.74
(dd, J ) 15.7, 5.8 Hz, 1 H, NCH2), 4.12 (dd, J ) 15.7, 3.4 Hz,
1 H, NCH2), 5.68 (s, 1 H, NCH), 5.74 (d, J ) 9.2 Hz, 1 H,
dCHSi), 5.90 (ddd, J ) 9.2, 5.8, 3.4 Hz, 1 H, HCd), 7.40-7.82
(m, 4 H, arom); 13C NMR -1.4 (SiMe3), 43.5 (NCH2), 81.3
(NCH), 123.3 (HCd), 123.4 (HCd), 129.9, 131.5, 132.3, 133.2,
139.9, 143.9 (arom), 167.1 (CdO); IR 3300 (br), 1683; LRMS
m/z 261 (m, 14), 246 (10), 232 (100), 204 (26), 177 (10), 133
(12), 130 (11); HRMS m/z 261.1185 (C14H19NO2Si requires
261.1186).
P h otoch em istr y of r-Silyla m id oa ceton a p h th on e 13. A
solution of the amidonaphthone 13 (53 mg, 0.13 mmol) in CH3-
CN (100 mL) was irradiated with Pyrex glass-filtered light
under N2. The reaction progress was followed by UV, TLC,
and 1H NMR which showed that >90% of 13 consumed after
3 h. The photolysate was concentrated in vacuo to give a
residue which was subjected to column chromatography
(Alumina, 20% ether/cyclohexane) to yield 6 mg (11%) of
recovered amidonaphthone 13, ca. 2 mg (5%, 1H NMR integra-
tion) of benzyl carbamate 43, 3 mg (6%) of 1-[(benzyloxy)-
carbonyl]-3-(2-naphthyl)-3-[(trimethylsilyl)oxy]azetidine (44),
6 mg (15%) of 1-[(benzyloxy)carbonyl]-3-hydroxy-3-(2-naph-
thyl)azetidine (45), 0.5 mg (1%) of 1-[(benzyloxy)carbonyl]-2-
(trimethylsilyl)-3-hydroxy-3-(2-naphthyl)azetidine (46), and 3
mg (14%) of 2-acetonaphthone.
30: 1H NMR 0.02 (s, 9 H, SiMe3), 2.87 (s, 3 H, CH3O), 3.75
(dd, J ) 15.7, 6.0 Hz, 1 H, NCH2), 4.52 (dd, J ) 15.7, 3.8 Hz,
1 H, NCH2), 5.81 (d, J ) 18.7 Hz, 1 H, dCHSi), 5.82 (s, 1 H,
NCHO), 5.96 (ddd, J ) 18.7, 6.0, 3.8 Hz, 1 H, CHd), 7.47-
7.86 (m, 4 H, aromatic); 13C NMR -1.3 (SiMe3), 43.9 (NCH2),
49.3 (CH3O), 85.9 (NCH), 123.5 (dCHSi), 123.6 (CHd), 129.9,
132.0, 133.1, 133.4, 139.7, 140.5 (arom), 167.4 (CdO); IR 1697;
LRMS m/z 275 (M, 15), 261 (21), 260 (100), 244 (19), 224 (12),
205 (12), 202 (35); HRMS m/z 275.1347 (C15H21NO2Si requires
275.1342).
In Aceton e. Irradiation of a solution of (silylpropyl)-
phthalimide 11 (500 mg, 1.91 mmol) in 200 mL of acetone with
Vycor-filtered light under N2 for 20 h (58% conversion of 11)
gave after concentration in vacuo and chromatography of the
residue (silica, 1:4 EtOAc-CH2CH2) 63 mg (22%) of 27, 16 mg
(8%) of 28, 82 mg (28%) of 29, and 27 mg (9%) of 30.
In 30% H2O-MeCN. A solution of 11 (220 mg, 0.84 mmol)
in a solution of 65 mL of MeCN and 35 mL of H2O was
irradiated with Vycor-filtered light under N2 for 20 min. The
photolysate was conentrated in vacuo to give 153 mg (96%) of
28, a crystalline solid (mp 121-124 °C). One recrystallization
from acetone-hexane gave 144 mg (91%) of pure 28 (mp 123-
125 °C).
44: 1H NMR 0.03 (s, 9 H, SiCH3), 4.35 (m, 4 H, H-2 and
H-4), 5.13 (s, 2 H, PhCH2), 7.29-7.91 (m, 12 H, aromatic); 13
C
NMR 1.44 (SiCH3), 64.4 (C-2 and C-4), 66.9 (PhCH2), 73.3 (C-
3), 123.5, 123.5, 126.3, 126.4, 127.6, 128.0, 128.1, 128.2, 128.5,
and 128.7 (aromatic, CH), 132.8, 132.9, 136.6, and 141.0
(aromatic, ipso), 156.6 (NCdO); IR 3059, 2955, 1709, 1420,
1356, 1252, 1105, 843, 750; LRMS m/z 405 (M, 1.24), 390 (22),
314 (10), 299 (13), 243 (12), 242 (43), 241 (20), 227 (28), 171
(13), 170 (100), 155 (32), 141 (16), 128 (22), 127 (18); HRMS
m/z 405.1727 (C24H27NO3Si requires 405.1760).
45: 1H NMR 3.23 (s, 1 H, OH), 4.29 and 4.41 (AB q, J ) 9.3
Hz, 4 H, H-2 and H-4), 5.11 (s, 2 H, PhCH2), 7.31-7.90 (m, 12
H, aromatic); 13C NMR 64.3 (C-2 and 4), 67.0 (PhCH2), 71.9
(C-1), 122.7, 123.3, 126.4, 126.5, 127.6, 128.0, 128.1, 128.2,
128.5, and 128.8 (aromatic, CH), 132.8, 133.0, 136.5, and 140.1
(aromatic, ipso), 156.7 (NCdO); IR 3392, 3055, 2952, 1684,
1429, 1356, 1185, 1105, 748; LRMS m/z 333 (M, 0.5), 242 (15),
198 (8), 178 (11), 171 (38), 170 (100), 156 (12), 155 (84), 142
(15), 141 (54), 134 (18), 128 (74), 127 (44); HRMS m/z 333.1360
(C21H19NO3 requires 333.1365).
P h otoch em istr y of r-Silyla m id oa cetop h en on e 12.
A
solution (75 mL) of CH3CN containing 327 mg (0.92 mmol) of
the amido phenone 12 was irradiated with Corex glass-filtered
light under N2 for 1 h (>90% conversion). The photolysate
was concentrated in vacuo giving a residue which was sub-
jected to column chromatography (Alumina, 20% ether-
cyclohexane) to yield 31 mg (9%) of recovered amidophenone
12, 73 mg (22%) of 1-[(benzyloxy)carbonyl]-3-phenyl-3-[(tri-
methylsilyl)oxy]azetidine (40), 35 mg (13%) of 1-[(benzyloxy)-
carbonyl]-3-hydroxy-3-phenylazetidine (41), 29 mg (9%) of
1-[(benzyloxy)carbonyl]-2-(trimethylsilyl)-3-hydroxy-3-phen-
ylazetidine (42), and trace quantities of acetophenone and
benzyl N-[(trimethylsilyl)methyl]carbamate (43). The product
40 was converted to 41 with the treatment by 1.0 N aqueous
H2SO4 in THF at 25 °C.
46: 1H NMR 0.2 (br s, 9 H, SiCH3), 4.24 (d, J ) 8.8 Hz, 1
H, H-4), 4.34 (br s, 1 H, H-2), 4.68 (br s, 1 H, H-4), 5.11 (s, 2
H, PhCH2), 7.29-7.86 (m, 12 H, aromatic); IR 3500-3400,
1694, 1682, 1417, 845, 748; LRMS m/z 405 (M, 4.96), 404 (5),
391 (12), 390 (38), 314 (28), 299 (17), 282 (23), 270 (34), 252
(10), 242 (24), 241 (100), 236 (25), 227 (30), 206 (19), 192 (52),
170 (98), 155 (70), 141 (19), 128 (32), 127 (41), 107 (22); HRMS
m/z 405.1775 (C24H27NO3Si requires 405.1760).
P h otoch em istr y of γ-(Tr im eth ylsilyl)bu tyr op h en on e
(14). A 0.5 mL CD3CN solution containing 5 mg (0.024 mmol)
of the phenyl ketone 14 was irradiated with Corex glass-
filtered light for 35 min. The reaction progress was monitored
by 1H NMR. The yield of the photoproducts, acetophenone,
1,4-diphenyl-1,4-butanedione, and vinyltrimethylsilane, were
40: 1H NMR 0.00 (s, 9 H, SiCH3), 4.28 (s, 4 H, H-2, and
H-4), 5.10 (s, 2 H, PhCH2), 7.21-7.43 (m, 10 H, aromatic); 13
C
NMR 1.3 (SiCH3), 64.5 (C-2 and C-4), 66.7 (PhCH2), 73.0 (C-
3), 124.9, 127.7, 127.9, 128.0, 128.4, and 128.6 (aromatic, CH),
136.5 and 143.7 (aromatic, ipso), 156.4 (NCdO); IR 3018, 2959,
1693, 1216, 1116, 769; LRMS (CI) m/z 356 (M + 1, 3), 266 (5),
264 (3), 193 (22), 192 (100), 191 (62), 190 (6), 179 (7), 178 (9),
177 (57), 130 (8); HRMS (CI) m/z 356.1693 (M + 1, C20H26
NO3Si requires 356.1682).
-

3314 J . Org. Chem., Vol. 61, No. 10, 1996
Lee et al.
determined to be 80%, 10%, and 100% (based on conversion
80%), respectively, by H NMR integration.
3480, 2950, 2229, 1246, 836; LRMS m/z (relative intensity) 245
(M, 14.2), 230 (39), 217 (34), 216 (19), 202 (75), 169 (13), 154
(10), 146 (10), 145 (100), 131 (21), 130 (52), 127 (18), 119 (17);
HRMS m/z 245.1215 (C14H19NOSi requires 245.1236).
Qu a n tu m Yield Mea su r em en ts for P h otor ea ction s of
Keton es 12-15. Quantum yields for photoreactions of the
2-naphthyl ketones 13 and 15 were determined by use of the
2-acetonaphthone and triethylamine photoreduction reaction21
as an actinometer. The Norrish Type II cleavage of buty-
rophenone22 was used as the actinometer in quantum yield
determinations of the photoreactions of the phenyl ketones 12
and 14. All photoreactions were conducted to low conversions
(4-17%) and quantitative analyses of products and/or starting
materials was carried out by use of 1H NMR spectroscopic
methods.
1
P h otoch em istr y of γ-(Tr im eth ylsilyl)bu tyr o-2-n a p h -
th on e (15). A 0.5 mL CD3CN solution containing 5 mg (0.018
mmol) of the naphthyl ketone 15 was irradiated with Vycor
glass-filtered light for 100 h. The yield of photoproducts,
2-acetonaphthone, 1,4-di(2-naphthyl)-1,4-butanedione, and vi-
nyltrimethylsilane, were determined to be 61%, 100%, and
1
19%, respectively as determined by H NMR integration.
P h otoch em istr y of [γ-(Tr im eth ylsilyl)bu tyr yl]-p-cy-
a n op h en on e (16). A solution of CH3CN (100 mL) containing
71 mg (0.028 mmol) of the cyano ketone 16 was irradiated with
Corex glass-filtered light for 30 min (90% conversion). The
photolysate was concentrated in vacuo to give a residue which
was subjected to preparative TLC (Silica gel, 30% ether-
hexane) separation to yield 27 mg (67%) of 4-cyanoacetophe-
none (49), a trace of 1,4-bis(4-cyanophenyl)-1,4-butanedione
(50), 8 mg (11%) of 1-(4-cyanophenyl)-2-(trimethylsilyl)-1-
cyclobutanol (51), and 5 mg (7%) of recovered 4-cyano ketone
16.
Ack n ow led gm en t. Support of this work by NSF
(CHE-17725, INT-17290 for PSM) and KOSEF (CBM
of POSTECH and International Cooperative Research
for UCY) is acknowledged.
A 0.5 mL CD3CN solution in a NMR tube containing 7 mg
(0.028 mmol) of the cyano ketone 16 was irradiated with Corex
glass-filtered light for 20 min. The yield of photoproducts, 49-
51 and vinyltrimethylsilane, were 91%, 1%, 7%, and 91%,
respectively.
Su p p or tin g In for m a tion Ava ila ble: Copies of spectra for
new compounds characterized in this work (52 pages). This
material is contained in libraries on microfiche, immediately
follows this article in the microfilm version of the journal, and
can be ordered from the ACS; see any current masthead page
for ordering information.
51: 1H NMR 0.09 (s, 9 H, SiCH3), 1.85 (br s, 1 H, OH), 1.91
(m, 2 H, H-3), 2.02 (m, 1 H, H-4), 2.35 (m, 1 H, H-2), 2.68 (m,
1 H, H-4), 7.63 (s, 4 H, aromatic); 13C NMR -1.8 (SiCH3), 14.3
(C-3), 37.5 (C-4), 37.8 (C-2), 78.6 (C-1), 110.6 (CN), 118.9 and
153.8 (aromatic, ipso), 125.2 and 132.3 (aromatic, CH); IR
J O9522623
(22) Bartrop, J . A.; Coyle, J . D. J . Am. Chem. Soc. 1968, 90, 6584.