Patai S., Rappoport Z. 1997 The chemistry of functional groups. The chemistry of dienes and polyenes. V. 1 / 0359 480

TABLE 8. Dienes through the Julia reaction

Aldehyde		Sulphone			Product	Reference
		O	P		O	P
	PhO2 S	N			N
		H			H
						96a
O	CHO				O
COOMe					COOMe
P = Me3 SiCH2 CH2 O
					O
CHO					O
MeOOC
		O			OP	96b
				O	COOMe
OMe	PhO2 S	OP
		P = t-BuPh2 Si
					OMe

continued overleaf

389

TABLE 8.	(continued)
Aldehyde			Sulphone	Product
				O
			SO2 Ph	O
	O		COOMe	OP
	O
				COOMe
CHO
	OP
	P = t-BuMe2 Si		OMe
				OMe
			P′O	O
OHC	OP COOMe			O
		P′O
			O	OP′
			O
O				OP COOMe
	H OP′	PhO2 S	OP′
P = Me3Si;P′ = t-BuMe2Si				O
				H

P′O

390

Reference

96c

96d

		OP
			OH		OH
	OMe	OP′	O	O		OP
OHC		O	O	O	OMe		96e
						OP′
		O
			SO2 Tol			O
	P = t-BuMe2Si;P′ = MeOCH2
						O
				P′O	O
O	COOMe				O
	P′′O	P′O	O
			O		OP		96f
O					OP′′COOMe
	OP		OP
	P = t-BuMe2Si;P′= SEM;P′′= TES		PhO2S		O

PO

391

392

TABLE 9. Polyenes through the Julia reaction

Aldehyde	Sulphone	Product	Reference
	ArO2 S
CHO			97a
		HO	OCOMe
COOMe		•
CHO
HO	SO2Ph
		HO	OCOMe

COOMe	•	97b
HO

9. Synthesis of conjugated dienes and polyenes

SO2 Ph	O
O	N
	+
O	1. n-BuLi
	2. A c2 O, Py
	3. t-BuOK
	O
O	N

O

P iperine

	O
SO2 Ph	N
OHC
+
( )14	1. n-BuLi
	2. A c2 O, Py
	3. t-BuOK, r.t.
O
( )14	N
Trichonine

393

(60)

(61)

Backvall and Juntunen and Fuchs and Braish have developed (E)-2-phenylsuphonyl- 1,3-dienes prepared under Julia conditions as versatile synthones for a variety of organic transformations103. These dienes undergo facile Diels Alder reaction and subsequent 1,4- elimination of sulphinic acid by base to generate a new diene (equation 62)103a. An elegant extension of this method is to use chiral sulfinylmaleate which, on Diels Alder reaction and elimination of the sulfinyl group, generates an optically active diene for further applications (equation 63)104.

PhO2 S		PhO2 S
+	∆
COOCH3			COOCH3
CH3			CH3
		NaOMe	(62)

COOCH3

CH3

394	Goverdhan Mehta and H. Surya Prakash Rao
S	COOBn	OMe	COOBn
Tol			(63)
O		Eu(fod)3
	COOBn	MeO	COOBn

Allyl sulphones can be converted to dienes by alkylation and elimination of sulphinic acid under basic conditions (equation 64)105. Several vitamin A related polyenes have been synthesized following this two-step protocol (Table 10)106. The poor leaving-group ability of the arylsulphonyl group requires treatment with strong base for elimination. However, elimination of the allylsulphonyl group takes place readily under palladium catalysis (equation 65)107. Vinyl sulphones can be converted to dienes via Michael addition, alkylation with allyl halides and elimination of sulphinic acid sequence (equation 66)108.

SO2 Ph

1. t-BuO −K+ , MeOOC	Br
2. KOH

(64)

COOH

SO2 Ph

+

AcO

COOCH3

O

1. (Ph3 P)4 Pd

NaH (65)

2. DBU

COOCH3

O

9. Synthesis of conjugated dienes and polyenes					395
O		O
PhO2 S			+
1. CH3 O	−	−	2Na	O
			O
2. CH2 CH		CH2	Br
O 3. t-BuOK			H3 CO		O
O					O

(66) An alternative approach to the synthesis of 1,3-dienes is by elimination of benzenesulphinic acid from homoallylic sulphones under basic conditions. This method has been used for the synthesis of a pheromone constituent of the codling moth (equation 67)109.

SO2 Ph

+	PO	I
	(	)7
		1. n-BuLi	(67)
		2. H3 O+
		3. t-BuOK, ∆

HO

P = THP

IV. CONCERTED REACTIONS

A. General Aspects

Symmetry-allowed concerted reactions such as retro Diels Alder reactions and electrocyclic ring-opening reactions are popular methods for releasing the diene component for further manipulations110. As the reactions take place via symmetry-allowed processes111, the diene products can be obtained with high stereochemical purity. Extrusion of molecules such as sulphur dioxide, nitrogen, oxygen and carbon dioxide from cyclic substrates is another commonly used methodology for the stereoselective generation of dienes.

B. Extrusion of Neutral Species

1. Sulphur dioxide

Extrusion of sulphur dioxide from cyclic systems leading to dienes has proved to be a synthetically useful reaction112. Thermolysis of cis- and trans-2,5-disubstituted sulpholenes, which can be readily obtained through regioand stereoselective alkylation, proceeds in a stereospecific manner affording 1,3-dienes of high stereochemical purity, as predicted by symmetry rules (equations 68 and 69)113. On the other hand, a photochemical process is not completely stereospecific (equation 68)114. 2,5-Dialkylative cyclization

396

TABLE 10. Synthesis of vitamin A and related compounds through allyl sulphones

Allyl Sul phone	Electrophile	Product	Reference
SO2 Ph			CH2 OA c
			106a
Cl	CH2OA c
CH2 OH	Br		CH2OH
			106b
SO2 Ph
SO2Ph			CH2OH
			106c
O

SO2 A r Br	CHO
	CHO
A r : C6 H5OC6 H4	106d

9. Synthesis of conjugated dienes and polyenes

397

can be performed on 3-sulpholene with 3-chloro-2-(chloromethyl)propene and sulphur dioxide extrusion from the [3.2.1]bicyclic product results in a seven-membered cyclic diene (equation 70)115. Regioselective monoalkylation of sulpholene derivatives can be performed via their 2-stannyl or 2-manganese derivatives with vinyl iodides in the presence of a Pd0 complex116. Sulphur dioxide extrusion from the products result in trienes with well-defined stereochemistry (equation 71).

∆

SO2
hν	+

			60%			25%		(68)
						+
						10%
		C5H11	∆				C5H11	(69)
S			− SO2
O2
R1	R2			R1	R2		R1	R2
		1. 2 eq. LiHMDS				∆
						− SO2		(70)
S		2. I	I		S
O2					O2

LiHMDS = lithium hexamethyldisilazide

	+	I	1. n-BuLi, (n-Bu)3 SnCl
			2. Pd(PPh3 )4
	S
			3. NaHCO3 , EtOH, 60˚C
	O2	(71)

398	Goverdhan Mehta and H. Surya Prakash Rao

The carbanion generated from deprotonation of the ˛-carbon atom of sulpholene reacts with aldehydes and ketones to give alcohols. Sulphur dioxide extrusion from the products results in (E)-˛-hydroxy-1,3-dienes (equation 72), or dehydration followed by thermal desulphonylation results in trienes117. Dienones can be obtained if the initial condensation is conducted with an aldehyde, followed by oxidation and sulphur dioxide removal117.

O

+

S

O2

OH

1. LiHMDS

(72)

2.Pd(PPh3 )4

3.NaHCO3

Even though sulphur dioxide extrusion from sulpholene derivatives is generally conducted either by heating in a non-polar solvent or in the presence of base118, alternative reagents such as LAH119, and finely dispersed potassium metal120 are also used. Syntheses of some tetrasubstituted butadienes were achieved by treating the corresponding sulpholenes with ultrasonically dispersed potassium metal in the presence of water (equation 73)120b.

	K, ) ) ))
S
	t-BuOH
O2

(73) The Diels Alder adduct of sulpholene and cyclopentadiene is a useful starting material for substituted diene synthesis121. The diene moiety is unmasked by retroDiels Alder reaction and sulphur dioxide extrusion under flash vacuum pyrolysis

conditions (equations 74 and 75)122,123.

SO2

		CHCH2 Br	(74)
1. n-BuLi, C3H7CH			3. FVP, 650˚C
2. n-BuLi, Me3 SiCl			4. CH3OCHCl2 , TiCl4

CHO			WS 1228A
	Hypotensive vasodilator