Eric Block
University of Missouri-St. Louis st. Louis, Missouri 63121
Organic Sulfur Compounds in Organic Synthesis
Organic chemists have synthesized numerous new molecules of novel and intricate structure and have duplicated many of the most complex and reactive naturally occurring molecules such as alkaloids, vitamins, hormones, and nucleic acids. Although most of the functional groups possessed by these molecules (and their synthetic precursors) are described in sophomore organic chemistry courses, the intricate juxtaposition of these fundamental units creates exceptionally challenging synthetic problems. The classical methods of organic synthesis, while satisfactory for many relatively simple molecules, often prove unworkable for more complicated systems. The modern synthetic chemist requires reagents that are exceptionally selective, stereospecific, and efficient, while a t the same time being readily prepared, easy to use, and economical (important considerations if the synthetic objective is to be marketed). To this end he has employed photochemical and electrochemical procedures and has explored the use in synthesis of catalysts and reagents involving most of the elements in the periodic chart. Thus, organic (as well as inorganic) compounds of boron, phosphorus, sulfur, silicon, tin, aluminum, nickel, copper, and lithium, among others, are being used routinely in organic synthesis. The application of organic compounds of sulfur in organic synthesis will be the subject of this essay. In the execution of a synthesis certain simplifying procedures may he utilized, for example: Induced Proximity. Bond formation between two bulky molecules may be facilitated if the molecules are first joined by a temporary bridging element. The desired bond(s) can then be made in an intramolecular, rather than the more difficult intermolecular, fashion and the bridging group then removed (extruded). Alternatively, a temporary bridging group may be used to bring distant atoms of the same molecule within bonding distance (in effect, reducing the entropy requirements for the reaction), or to pin back bulky groups in a molecule until the construction of the remainder of the molecule has been completed. Activating or Protecting Groups. An activating group may be introduced which facilitates bond formation, desired rearrangements, or other reactions, Alternatively, groups may be introduced which prevent reactions at a particular site. Such activating or protecting groups may be connected directly to the site whose reactivity is to be modified or they may be sterically proximate, i.e., act as neighboring groups. I n both cases major alterations in reaction rates, product distribution, and product stereochemistry can be achieved. Asymmetric Induction. An optically active reagent 8 14
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Journal of Chemical Education
may be employed to induce asymmetry a t a formerly optically inactive center. The wondrous facility with which nature accomplishes the most complex syntheses undoubtedly reflects the widespread occurrence of natural biochemical processes analogous to those described above. Sulfur compounds have often been the basis of the above described procedures (both in vitro and in vivo) as well as numerous other methods of molecular construction, many of which involve gentle alternatives to standard reactions. The particular suitability of sulfur compounds lies in their ready availability, considerable versatility, and unique properties. Organically bound sulfur may be introduced into a molecule via an electron rich, electron deficient, or radical sulfur intermediate 6' 6-
(RS-, RS-X, or RS ., respectively) as well as in combination with other elements (particularly oxygen, nitrogen, and halogen). Once incorporated into a molecule, the sulfur function may he modified with ease to any of a variety of diierent valence states, each with its own characteristic chemistry including, in particular, the ability to stabilize adjacent positive, negative, or radical centers. A further attractive feature of organically bound sulfur is the great variety of methods which can be used to cleave carbon-sulfur bonds, including photolytic, thermolytic, electrolytic, and catalytic methods as well as direct chemical methods involving attack at carbon displacing sulfur or the reverse (i.e., sulfur extrusion from episulfides with phosphines (1)). These methods may serve to form different useful intermediates or rearrangement products or to remove the sulfur once it has served its prupose. For convenience the synthetic examples to be presented will be classified broadly as methods for the formation of double or single bonds and subclassified according to the type of sulfur function present. Below are the formulas for a number of basic types of organic sulfur compounds discussed on the pages to follow.
R-S-R
Sulfide
RSH Thiol
R&-o~I~ Alkoxyaulfonium
RJS*
Sllifonium Sdt
RSSR
Disvlfide
-
Salt
RA-~H. RI+CH, Sulfonium Ylrd
0
0
RAa
RSR
Sulfoxide
0 Sulfone
I
0
iI
R&O Oxosulfonium Salt
0
RSNHR Sulfinsm~de
0
I
R L C H , t, RA=cH~ -
Oroaulfonium Ylid
R&=S
(RXhC=S
Thioketone
Thionoosrhonate (X=O) Trithiooarbnnate (X=S)
(RS),CR'R" Thiosoetal
R'
R I
>d: I R" R,,, "Tetravalent Sulfur"
Table 2.
The Corey-Winter Olefin Synthesis
Methods for the Formation of Carbon-Carbon Double Bonds
The transformation of a-halosulfones into olefins upon treatment with base, first observed by Ramberg and Backlund in 1940, has been studied in considerable detail and is believed to proceed by the sequence indicated
The reaction is general for molecules containing the structural elements of a sulfonyl group, an a-halogen (or other suitable leaving group), and at least one a'hydrogen atom. With few exceptions the RamhergBicklund reaction allows the clean replacement of a sulfonyl group by a double bond. The required a-halogen atom may he introduced by treatment of the cor-
carhenes of type I, formed by treatment of th'ionocarbonates or trithiocarbonates with various trivalent organophosphorus compounds
e
responding a-sulfonyl carbanion (RR'CHSO&R1'R"'; prepared, from the reaction of the parent sulfone with a strong base such as an alkyllithium) with a source of X+(BrCN, I2 and C1,CSOIC1 are convenient sources of Br+, I+, and C1+, respectively (2)). Several typical synthetic applications of the Ramherg-Backlund reaction are listed in Table 1. The first two entries exTable 1.
Thionocarbonates are readily prepared from uic-diols by a number of routes including a one-step reaction with thiocarhonyldiimidazole
Some Synthetic Applications of the Romberg-Backlund Reaction
Sulfone
Product
Yield
Reference
(2)
Sulfides
Examples of a "two-fold extrnsion" approach to olefin synthesis (I1 +111) are cited by Barton (8)
The leaving group here is C2HaS03-.
emplify the use of sulfur bridges in facilitating bond formation through inducing proximity of the carbon atoms to he joined. Thiocorbonyl Compounds
A valuable stereospecific olefin synthesis, discovered by Carey and Winter (7), has been used with considerable success to prepare several highly strained olefins (see Table 2). The reaction is based on the stereospecific loss of carbon dioxide or carbon disulfide from Volume 48, Number 12, December 1971
/
815
These reactions probably proceed by way of episulfides which are known to afford olefins andphosphinesulfides on treatment with phosphines (1). Several elegant examples of the effective use of the sequence sulfur bridging-carbon-carbon bond formation-sulfur extrusion in complex systems are found in the studies of Woodward and Eschenmoser directed toward the total synthesis of vitamin BIZas illustrated below ($,lo).
boakk
NC
H
NC
H
Dibenzoylpemride
bo
HG
Introduction of Sulfur
Of the multitude of attempts made by Eschenmoser and his coworkers to join more highly substituted and sterically hindered lactam and enamide BIZcomponents related to IV and V, respectively, only the sulfur bridging sequence succeeded, leading to the observation (11) Whenever in the synthesis of complex organic molecules one is confronted with a situation where the success of an intermoleo ular synthetic process is thwarted by any type of kineticdly controlled lack of reactivity, one should look out for opportunities of altering. the structural stage in such a way that the critical synthetic step can proceed intramolecdarly rather than intermolecularly.
The technique of irradiating sulfides in trivalent organophosphorus solvents also provides a potentially useful method for desulfurization with concomitant carbon-carbon bond formation (Z), e.g.
*
H
Formation of Sulfur Bridge
The felicitous use of sulfur permitted the synthesis of 4,5-di-tert-butylimidazoleby Wynberg (12)
earbon-carbon bond formation followed by extrusion of sulfur'
n
Methods for the Formation of Single Bonds
Thioacetals, prepared by the interaction of thiols or dithiols with carhonyl compounds, have been widely used as protecting groups for the carbonyl function of ketones and aldehydes (the carbonyl group can be regenerated by hydrolysis promoted by mercuric or other metallic salts) or in the reduction of the carbonyl group to a methylene group (Raney nickel). Use of an optically active dithiol represents a novel means of preparing optically active ketones and derivatives (15)
racemic
(Substituents omitted for clarity)
Diastereomers
0
optically active
o~ticallvactive
'The csrbon-carbon bond formstion process is suggested to involve an episulfide which loses sulfur to the phosphine (1). ¶ T h e ability of divalent sulfur, in contrasl to oxygen, to stabilize adjacent crtrbonionic centers is well known although the precise mechanism of this stabilization (often ascribed to dorbital overlap) is still the matter of some controversy (14).
816
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Journal of Chemical Education
The finding that the a-protons of the cyclic thioacetal 1,3-dithiane and its derivatives are acidic,=that the anions formed by removal of the a-proton are stable below 0' and that the a ~ o n exhibit s good nucleophilic properties provides the basis for a method of nucleophilic acylation (Id), a process noteworthy in that the normal direction of polarity of the carbonyl group has effectively been reversed. Dithiane derivatives may be prepared through the interaction of carbonyl compounds (or their 0-acetals) with 1,3-propanethiol or through the base catalyzed reaction of active methylene compounds with 1,3-propanedithiolsulfonateesters (15)
A
ROOC COOR
,
\
.
. .
H ' 'H i-Pr Pr-i The l,3-dithiane anion may be reacted with a wide variety of compounds containing electrophilic centers including alkyl halides, ketones and aldehydes, epoxides, esters, nitriles, carbon dioxide, imines, deuterium oxide, organometallic halides, ethyl chloroformate and dimethylformarnide. The dithiane method has been applied to the preparation of one of the sex attractants of the hark beetle (VI), the synthesis of germyl and silyl ketones (such as VII), optically active ketones (VIII) and deuterioaldehydes (IX), the preparation of metacyclophanes (X and XI), the total synthesis of prostaglandins, stereospecific steroid syntheses (XII) (16) as well as the preparation of a variety of simpler molecules as illustrated below (17)
-
-
Novel utilization of the 1,3-dithiane ring for nonoxidative ketone transposition (XIII XIV) (18)and nonoxidative carbon-carbon bond cleavage3 (XIII XV) (19)have been described by Marshall and Roebke.
T h e mechanism of fhis reaction presumably involves nucleophilic addition to the carhonyl group followed by C-C fragmentation to a dithiane anion. Volume 48, Number 12, December 1971
/
817
0
II
RNHCNHR
R'Rt'C=O
Dimethylsulfoxide (DMSO), an excellent organic solvent, is of great value in organic synthesis as an oxidizing agent and, in the formof the methylsulfinylcarbanion (CHaS(O)CH,-), as a strong base and nucleophilic carbon source (20). The oxidation of alcohols to aldehydes or ketones utilizing DMSO is the basis of a number of procedures, such as those discovered by Barton (21) and PfitznerMoffat (Sob). The Pfitzner-Moffat method is one of the mildest and most selective procedures available for the oxidation of alcohols to carbonyl compounds and is particularly useful in reactions involving natural products such as alkaloids, carbohydrates, nucleotides and nucleosides. It can be carried out under essentially neutral reaction conditions; primary alcohols may be cleanly converted to aldehydes without the danger of overoxidation. Isomerization and oxidation of other sensitive functional groups in the same molecule (such as the thiol group) are minimized. Three examples of the Pfitzner-Moffat oxidation together with the proposed mechanism (requiring the intermediacy of dimethylalkoxysulfonium salts) are shown below.
Reagents: DMSO
+
(CH,),S=O
(CH,),S
CH8-CH2-
8
-
CH&=CH1
4
The methylsulfinyl carbanion, conveniently prepared through the interaction of sodium bydride with DMSO n n
forms substituted sulfoxides on reaction with electrophiles. These sulfoxides can then be made to undergo a variety of synthetically useful reactions, such as those illustrated on the nextpage for the reaction of methylsulfinyl carbanion with ethyl benzoate. Thus, the initially formed P-ketosulfoxide can be alkylated once or twice (A, A') (26, 27); the sulfinyl function can be removed affording ketones (B) (26-28); the p-ketosulfoxides can be converted to a-dicarbonyl compounds by treatment with phosphoric acid (C) (26), to 7-ketoestem by treatment with ethyl bromoacetate (D) followed by reduction (B) (29) and to p-keto-w-hydroxysulfides by treatment with mild acid (E) (B6). The p-keto-ahydroxysulfides can in turn be converted to glycols (F), glyoxals (G) or to a-keto alcohols (H) (26). Examples of the great utility of the sulfoxide function in more complex syntheses are shown on the next page for thesyntheses of ninhydrin (SO) (an important reagent for amino acid determinations), ecdysone (31) (an insect molting hormone) and illudin M (32) (a fungal sesquiterpenoid): In these syntheses, the sulfinyl group is introduced as an activating function, new carboncarbon or carhon-hetero bonds are formed and finally the superfluous sulfur containing group is removed. In some synthetic applications dimethyl sulfone can be used to advantage in place of DMSO (33). Finally, it should be mentioned that pyrolysis of sulfoxides represents a general synthetic route to olefins as in the following example (34)
+ Dicyclohexylearbodiimide
+ Pyridinium TriEuoroacetate (Base-Acid) Proposed mechanism (25) T H+
R-N=C=N-R
+
Removal of a proton from DMSO gives the methylsulfinyl carbanion. The negative charge of this strong, nucleophilic base is stabilized by the electron witbdrawing property of the sulfinyl group and also presumably by d-p orbital overlap
Ht
R-NH-C=NR
I I :S(CH& 0
-
11
CH,(CH,),,S-CH,
heat ---t
CH,(CHJ&H=CH,
(58460verall)
Sulfur Ylids
Ylids are substances in which a carbanion is attached 81 8
/
Journal o f Chemical Education
R'CH-CHCH,CH2C(CH3),0H H
b~ Ecdysone
HO 0
Volume 48, Number 12, December 1971
/
819
directly to a heteroatom bearing a positive charge (a so-called 'onium group, i.e., ammonium, phosphonium, sulfonium, oxosulfonium) (55). The 'onium group stabilizes the adjacent carbanion by electrostatic (coulombic) and, where possible, by resonance (d-p overlap) interactions. The ylids of greatest synthetic value are the phosphonium, sulfonium, and sulfoxonium ylids, respectively P~HC-c
PK=CH~,SS
H
XXI
(87%)
The basicity and nucleophilicity of the ylids depend on the properties of the substituents X and Y: if X and/ or Y are electron acceptors, such as cyano, carbonyl, or
0 II
3
&
P~CH=CH~P~
k
(60%)
no reaction
+
R2S-, the carbanion electron density will be lowered and the basicity/nucleophilicity diminished; conversely, substitnents which are electron donors (such as alkyl groups) will increase the carbanion electron density and enhance the basicity/nucleophilicity. Phosphorus and sulfur ylids are complementary in utility as shown in t,he transformation of cyclic ketones to XVI and XVII (36) and in the synthesis of the natural product, DL-rimuene XVIII (37). The sulfonium and oxosulfoniumylids are also complementary reagents since the former is a far more powerful methylene transfer agent with less stringent steric requirements than the latter, as indicated by the reactions of X I X (58), XX and XXI (36). Sulfur ylids are conveniently prepared from the corresponding 'onium salts by interaction with strong bases such as sodium methylsulfinyl carbanion
Several of the versatile applications of sulfur ylids in synthesis are indicated in Table 3.& Sulfur ylids may undergo several rearrangements such as the Stevens rearrangement (XXII -t XXIII) and the vinylogous Stevens rearrangement (XXTV -t XXV).= A -,
c,svc
% C ,;
I
R
I
*
R
XXII
..
-I
C-C S
R
xm
. .
XXN
XXV
The former reaction has been elegantly applied by Boelelheide and coworkers to the synthesis of cyclophane dienes (such as XXVI) (51) and trienes (XXVII)
J
x'
(CKO) CH,
+
CHZ~S(CH&
U
XVI
-
, 820
>
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XVIII Journal of Chemical Education
4 The original references should be consulted for details on the mecht~nismsof these interesting reactions. ' I n the terminology of the Woodward-Hoffmann rules (60) these two reactions are 11, 21 and [2, 31-sigmatropic rearrrtngements, respectively.
Table 3. Ylid
Sulfur Ylids in Organic Synthesis
Substrate
Product
Yield
(%I
Referenoe
0
II
PhC-CCPh
0
By II
C-MOK NH,
CH.
Ph-q=o
V A
F'hC
MPh
0%:
By rearrange "lent of
0
[2.2.2](1,3,5)cyclophane. 1,9,17-triene
XXVII
It has been suggested that the biosynthesis of squalene from farnesyl derivative may involve a vinylogous Stevens rearrangement (55). Support is provided for this theory by the studies of Baldwiu and other workers (55) on a novel procedure for the coupling of ally1 groups under mild conditions. Apparently both types of Stevens rearrangements can occur simultaneously (see below); a free radical mechanism has been demonstrated by Baldwin for at least one Stevens rearrangement (55).
Volume 48, Number 72, December 1971
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821
Sulfonium Salts
I n addition to serving as precursors to snlfonium ylids, sulfonium salts have been the basis of a number of other synthetic procedures, two of which are considered here. Trost has reported that S-methyl trimethylene sulfonium salts (S-methylthietanonium salts) afford ey!lopropant~sin a s~crrospwifivpmcrss ou trratment with t)ntvllithiurn. Tetrnvnlrut snlfur inrrrrnedixtes are invokkd (54).
The active intermediate is presumably the ion XXVIII + + PbSCH* tr PhS=CH* XXVIII
BF,-
Sulfones
Corey has devised a useful homologization procedure which was used in a key step in the stereospecific total synthesis of the dl CIScecropia juvenile hormone (55)
-
sBr + c'C,H,SCH&u"
Synthetic advantage has been taken of the relative weakness of the carbon-sulfur bond in the synthesis of a variety of polycyclic hydrocarbons via pyrolysis (at temperatures ranging from 300 to 700°C) of sulfones. This method can be applied to unstable compounds if a flow system with a cold trap is used. Typical syntheses are outlined in Table 4. Table 4.
Hydrocarbon Synthesis via Sulfone Pyrolysis Tern-
cH'l
perture
DMF
700
&
Svlfone wSCeH5 Na7-
CH, [+CJI.]
('C)
product
Yield
(%)
40-50
Referm e
(2)
-
CI8Cecropisjuvenile hormone a-Halosulfides
Eschenmoser has described a novel electrophilic methylation procedure for introducing methyl groups into the 5 and 15 positions of the corrin ring (11).
Unsaturated Sulfides
A novel method for the construction of carbon-carbon bonds involves the thio-Claisen rearrangement (the sulfur analog of the Claisen rearrangement) of allylvinyl sulfides. Carrying out the rearrangement in the presence of mercuric oxide converts the presumed thiolaldehyde intermediate to the corresponding aldehyde. Two examples are given below (59, 60). The sequence illustrated in the first example failed for alicyclic ketones with allyloxymethyltriphenylphosphonium ylid (59). 822
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Journal of Chemical Education
An elegant example of the use of a dihydrothiophene derivative (XXIX) in a stereospecific synthetic approach to trans-fused bicyclic systems by Stork and Stotter is depicted below (63).
Known Reactions
Thiophenes and Relafed Heterocycles
The readily available thiophene ring system, a potential four-carbon source (on sulfur removal) with the advantage of easy ring substitution, has been the basis of a number of synthetic efforts such as those pictured
LL
(54% yield from XXM )
The isothiazole ring, which becomes a three-carbon plus nitrogen source on sulfur removal, is ingeniously utilized in Woodward's total synthesis of colchicine (75), as indicated in part below.
(6l,68).
43"
optically active
Chiral has no detectable optical ~otivity(between 280-580 n d .
MeOq :q
Md)
.
2 NaBK
Md) 0
Table 5. Sulfur reagent
C3HrSH RCHIOGL (+EtaN CHCOOSOlAr CHIOCH?OSOICH~
+ CHaNd
Additional Applications of Sulfur in Synthesis ~
~
Reaction achieved
Reference
Active Hydmgen source (i.e.. in Cr (11) deiodinat~ons) Olefin synthesis Mild method for cleavage of ethers An oxyaikylatingagent
(66)
(64) (66) (66)
The nucleophilio equivalent of -CH=CHCHO
Useful method for cis-tmns isonerimtion of double bonds , "
Effects the conversions
PhSFs (followed by LiAIH.)
R~*CH-CHSP~
CHIS(O)NHA~ n-CxH6Lr Ph8(ORh (R=PhC(CFdd
(63)
EKeots the conversion -ROH --t R-H under mild conditions partieulkrly useful for sllylio and benrylie hieohols Nueleo~hiliocarbon reagent okhn synthesis
O-Alkyl o1eava.e of methyl esters Dehydration of Aloohols
(71) (7s) (73)
(74)
0
Space limitations preclude a detailed discussion of a variety of other synthetically useful and mechanistically interesting procedures involving organic sulfur compounds. Table 5 lists a few of these methods together with leading references which should he consulted for details. Acknowledgment is made t o the donors of The Petroleum Research Fund, administered by the American Chemical Society, for support during the preparation of this paper. Literature Cited (11 SANDER, M., Cham. Rev., 66, 326 (1966). E . J.. A N D B L O C R . EJ. .. 010. Chem., 34, 1233 (1969). (2) COREY, (31 PAPUETTE. L. A,, A N D PXILIPB. J. C.. J . AmW. Chem. Soc.. 91. 3973 (1969). NEUREITER. N. P.,J . O w . Cham., 30,1313 (1865); D10 is thesolvent. C n o w ~M. . W.. J . Amcr. Chem.Soc.. 74. 1225 118.521. (a1 E c n a ~ ~ i c n F., . Diss. Ab6t?., 15,706 ( 1 9 5 5 j . ( b ) MEYERS.C. Y., MALTE,A. M., AND MATTHEWS,W. S., J. Amei. Chem. Soc.. 91, 7510 (19691. The halogen soureeis CCL. C o n ~ r E. , J., CAREY.F. A.. A N D WINTER.R. A. E., J . Amcr. Chcm. Sac.. 87, 834 (1965): COREI, E. J.. AND SIULMAN. J. I., Tebohedron Lett.. 3655 (18681, and references therein. B*n=on, D. H. R.. A N D WLLLIB, B. J., Chem. Commun.. 1225 (1970); B*n=oii. D. H. R., SNITX, E . H., A N D WILLIB, B . J., Chcm. Commun.. .?.,a
,."7"\
Wrmsdnc. H. A N D AE. DE. GROOT,Chem. Commun.. 171 (1955). Coner. E. J., m n MITE*, R. B., J . Amsr. Chem. Soc.. 84, 2938 (1962). For recent referenoes, see S m n m a . D., Anoem. Chem. I d . Ed.. 8. 638 ,,ace,
Woonw~noR . . B.. PATEHETT, A. A,. BARTON. D. H. R.. IYEB,D.A., A N D K e ~ r u R. . B.. J . Cham. Soc., 1131 (1957). J m e s . J. R.. A N D GRAYBRAN. R.. Chem. Commwn.. 141 110701~ . ~ ~ . ~ -...,. ~ e f e r e k e sfor the reactions cited as well as many other eramples of t h e utility of the dithiane method may be found in SEEB*DX, D.. Suntheria. 1, 17 (19591 and F ~ s s E n ,M., A N D F r z a e ~L., , "Reagents for Organic Synthesis," Wiley-Interscience, New York. 1969, pp. 182fi. For a useful procedure for the hydrolysis of 1.3-dithianes, see Y m e m E. and Fncns, P.L., J. Ore. Chem., 36, 366 (1971). M n n a n * ~ ~J . A.. A N D ROEIIHE. H., J . 070. Chcm., 34, 4188 (1968). A180 see ref. (76) for the conversion of a ketone to zn =-diketone by a similar method. MARSHALL. J. A,. A N D ROEBXE.H.. Tetrahedron Lett., 1555 (1870). For general summaries of synthetio applications of DMSO, see (a) FIEBER. M.. A N D FIESEX,L.. "Reagents for Orgsnio Syntheais." 2. WiLy-Interscience, New York. 1969, pp 157: (bl D u n a ~ .T., .n "Advances in Organic Chemistry" (Edflors: TATLOR, E . C. A N D W r s ~ ~ H.), n c Interseienoe, New York. 1869, Vol. 6. BAXTON, D. H. R., G ~ n n m nB. , J.. A N D WIGATMAN. R. H.. J . Chem. ~~~
Ror.
~~~
IS55 (l9F.dJ ---~..".,.
JoPms, J . B., A N D WIOFIELD, D. C., Can. J . Chcm., 44, 2517 (1966). Bnoon, A. G.. A N D P ~ s n cJ.~ B., , J . OR. Chem., 30, 2566 (18651. WZINBHENKER, N. M.. A N D GREENE.F. D., J . Amer. Cham. Soc.. 90, 506 (19681. FENBZLAU, A. H., A N D MOFFATT,J . 0.. J . Amei. Cham. Soe.. 88, 1762 (1966). RUBSLLL, G . A., A N D N U R O ~ G., J., J . Amer. Chcm. Soc., 88, 5498 ,7naa, ,.c"",.
GABBMAN. P. G.,A N D RICRMOND, G. D., J. O w . Chcm.. 31, 2355 (1966). C O ~ B YE., J., Awn Cn*ruovsxr, M.. J , Amcr. Chem. Soc., 86. 1638 11964). . . RU88EGL. G . A., AND O C H R M O ~ T C I ,L. A,, J . 070. Chem., 34, 3624 (19691.
824
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Journal of Chemical Education
RUBBELL. G. A.. SABOWIN. E. T . , HAMPREOHT. G.. J. Org, Chem.. 34, 2339 (1969). S ~ D D A G J. , B.. CnOm. A. D.. A N D F R I E D , J. H., J . Amel. Chem. Soc., 88,862 (1966). MATBUMOTO, T.. ET *I.. J . Amer. Chcm. Soo.. 90,3280 (1968). Hanss, H. 0.. A N D LAnaea, J. K . , J . 070.Chcm., 33, 61 (19681, ENTWIBTLE. I. D., A N D JOHNBTONE. R . A. W.. Chem. Commun.. 28 (19651. JonmoN. A. W., "Ylid Chemistry," Academic Press, N e w York. 1962. CO~EY E .. J.. A N D C n * r m v s ~ r .M.. J . Amer. Chem. Soc., 87, 1353 (19651. I n e b * ~ R. ~ . E.. AND M m n e n . L. N.,Tstrohedran Lctl.. 3453 (1964). COOK,C. E . , ConeGY. R . C., A N D W*LL. M. E., Tetrahedron Letl., 391 11965). HORTMANN. A. G., *NO ROBERTSON. D. A,. J . A m w . Chem. Soc., 89, 5874 (19671. Hmnra. T. M.. H~nnrs.C. M., m n C z n m r , J. C.. Tatrahedron Lctl.. 1427 (18681. HORTMANN, A. G.. J . Amw. Cham. Soc.. 87. 4972 (19651; also aee ref. (40).
BRAVO,P.. G*oorhao. G., *so UMANI-ROWCHI, A.. Tetrahedron Left. 679 (1969). TROBT.B. M.,
AND
-S*"d -- - ,107nl - ..- ,.
L&OCHELLE. R. W.. J. A m w . Chcm. Soc., 92,
\
(a) T n o s ~ B. . M., J . A m r . Chem. Soc.. 88, 1587 (19661; (bl For other
rynthetio applications of photoohemioal reactions of sulfur ylids and other sulfur oompounds, see BLOOK, E.. Quarterlu Repo~tson S d l w Chemist~y.4, 237 (1969). Coney. E . J.. J*UTEL*T, M.. AND OPPOLZER,w.. T&'ohedron Lclt.. 2325 (19671. Comr,E. J.;AND JAUTELAT. M.. J. Amer. Cham. Soc., 89, 3913 (1967). PATNE, G, B., J. Org. Chcm., 32,3351 (1967): 33. 1285 (1968). Joxasohi, C. R., A N D Saxnaeca, C. W., J. A m r . Cham. Soc., 90, 6852
,.""",. ,,oes,
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