Dienes stereospecific synthesis

The stereospecific synthesis of an A ring synthon of la-hydroxy vitamin D has been carried out. The ( )-allcene is cyclized to give the (E -c.xo-diene 155, and the (Z)-allcene affords the (Z)-e,xo-diene 156 stereospecifically[125,126]. These results can be understood by the cis addition and syn elimination mechanism. 

Overman, L.E., Petty, C.B., Doedens, R.J. Synthetic application of N-(acylamino)-1,3-dienes. Control of endo stereoselectivity by the acyl substituent, stereospecific synthesis of the analgesic tilidine, J. Org. Chem. 1979, 44, 4183-4185. 

In a similar manner, alkynes can undergo sequential carbometallation reactions, previously illustrated in equation (32).136 It is possible to combine carbocupration of alkynes with the use of a Michael acceptor as electrophile when that electrophile is a vinylphosphonium salt, carbocupration can be coupled to Wittig alkenation to result in a stereospecific synthesis of dienes via a one-pot, four-component, four carbon-carbon bond-forming reaction sequence.302... 

Coupling of n- allylic)paUadium complexes with an alkenylzirconium(IV) complex l,4-< enes.2 A recent stereospecific synthesis of natural (20R)-cholestanone-3 (4) involves coupling of the alkenylzirconium complex 2 with the jr-(allylic)palladium chloride dimer (1) of a (Z)-17(2U)-pregnene. The major product is a 1,4-diene (3), formed by regioselective attack of 2 at C20, the less hindered terminus of the allylic unit, and with inversion at C20. Coupling of 2 with the 7i-(allylic)palladium chloride dimer of the (E)-isomer of 1 results in a 1,4-diene epimeric at C20 with 3. Hydrogenation of the diene completes the synthesis of the desired natural cholestanone-3 (4). 

J. Jurczak, T. Bauer, and S. Jarosz, Stereospecific synthesis of 5,6-dihydro-2//-pyran system. High-pressure cycloaddition of l,2 3,4-di-0-isopropylidene a-D-galactopyranose-6-ulose to 1-methoxybuta-l,3-diene, Tetrahedron Lett., 25 (1984) 4809—4812. 

The complex formed on addition of cuprous iodide to a solution of a lithium dialkylamide in ether or tetrahydrofuran is effective in the reductive coupling of allylic halides to give 1,5-dienes with preservation of stereochemistry. This method has been used5 for the stereospecific synthesis of all-trans-squalene and (E,Z,Z,E) squalene from (E,E)- and (Z,JE)-farnesyl bromides, respectively. In an attempted synthesis of (3S)-squalene-2,3-epoxide, 4-[(4R)-2,2,5,5-tetramethyl-l,3-dioxolan-4-yl]butan-2-one (1) and the phosphonium iodide (2) were prepared.6 Unfortu-... 

Cuprates of the type Li CuR + i, where > 1, react with the carbonyl group of propynoate esters rather than give the conjugate addition product 61). Extension of the reaction of propynoate esters to vinylcopper compounds and allylcopper compounds affords a stereospecific synthesis of 1,3- and 1,4- dienes, respectively 64, 205). 

Stereospecific synthesis of (2Z,4E,6E)-3,7,11-trimethyl-2,4,6,10-dodecatetraene, trans (Cio)-allofamesene 49), isolated from Perilla fmtscem Makino, was realized by the ptdladium-catalyzed cross-coupling of 4,8-dimethyl-l,3,7-nonatrienyl-l,3,2-benzodioxaborole 48) with (Z)-2-bromo-2-butene. The benzodioxaborole derivative 48) was prepared by hydroboration of 4,8-dimethylnona-3,7-dien-l-yne 47), obtained via two steps from geranial, with 1,3,2-benzodioxaborole (Eq- 112) Bombykol and its geometrical isomers were also synthesized selectively... 

Stereospecific synthesis of alkenes. This Pd(0) complex is an efficient catalyst for the cross-coupling of vinylic halides with a variety of Grignard reagents. The resulting alkenes are obtained in 97% isomeric purity and in yields of 75-90%. This reaction is particularly useful for preparation of pure 1,3-dienes (equation I). ... 

Advantage may be taken of the selective hydroboration of alkynes as compared to alkenes by dicy-clohexylborane or disiamylborane (Section 3.10.4.3) to provide syntheses of dienes and their deuteriated derivatives e.g. equation 62). Dibromoborane-dimethyl sulUde may be used similarly (Section 3.10.4.4)." The approach has been used for the stereospecific synthesis of an allylic hydroxydiene (equation 63). ... 

This procedure has been utilized by Nicolaou to prepare the vinyl iodide (482) in the synthesis of lipo-toxins As and Bs (equation 111). The synthesis of vinyl iodides was also utilized by Bestmann in a stereospecific synthesis of (4 ,6 ,llZ)-hexadecatrienal. A Wittig reaction was used to create the ( )-al-kene (484), and the ( )-diene portion was synthesized via vinyl iodide (485) formation and coupling (Scheme 63). This method has been applied to the synthesis of > C-labeled vinyl iodide (488 equation 112). Labeled iodoform (486) was ma and the reaction conditions altered fhrni those employed by Takai and cowmkers in order to use smaller quantities of the valuable iodoform, relative to C1CI2. 

Dienes and 1 -enynes. Negishi et al.9 have extended the synthesis of 1,3-enynes by palladium-catalyzed cross-coupling of alkynylzinc chlorides with an alkenyl halide (8, 472) to a similar stereospecific synthesis of 1,5-dienes or 1,5-enynes by coupling an alkenyl halide with a homoallyl- or homopropargylzinc chloride. An example is the synthesis of the 1,5-enync I (equation I). This reaction... 

Stereospecific synthesis of 1,3-dienes. Corey et a .3 have described a new synthesis of 1,3-dienes based on the highly stereospecific cis addition of alkylcopper reagents to a, -acetylenic carbonyl compounds (3, 108). Thus the reaction of methyl 4-trimethyl-siloxy-2-nonynoate (l)4 in THF with divinylcopperlithium (1.25 eq) at —90° and then at — 78° affords the pure e(r adduct (2) in > 90% yield. Treatment of (2) with methanolic hydrochloric acid effects cleavage of the trimethylsilyl ether and lactonization to give (3). 

A general method for the stereospecific synthesis of conjugated ( , Z)-dienes has been reported and used to synthesize bombykol and its derivatives (Scheme 16). 

Palladium is released as Pd(0), ready for the next cycle. The relevance of this reaction to the subject of this chapter is that we have already used, and will use again, Z-bromoalkenes for the stereospecific synthesis of dienes. This is one way to make them. 

Syntheses of /(-(-i-)-myoporone (em-12) and / -(-H)-10,l 1-dehydromyoporone (ent-14) have been published recently (22). These rely on the use of methyl 5-citronellate as the source of the asymmetric carbon (Scheme 3). Of more general interest and application is an approach (23) which leads to the stereospecific synthesis of 9-dihydromyoporone, which contains two asymmetric centres. This synthesis formally constitutes a synthesis of myoporone. Still and Darst (23) have shown that hydroboration of -2,6-dimethylhepta-1,4-diene with thexylborane leads, with high diastereoselectivity, to the diastereomeric 1,4-diols (Scheme 4). Appropriate transformation of the yn-diol to the electrophilic iodo compound, followed by alkylation of the P-keto sulphoxide, gives... 

The success of the enantioselective Sharpless epoxidation to a large extent depends on the configuration of the double bond of an available substrate. Shibasaki et al. developed an efficient method of stereospecific synthesis of exocychc double bonds using 1,4-hydrogenation of conjugated dienes catalyzed by an arene-Cr(CO)3 complex [43]. Allylic alcohol 31b [44,45], a substrate for Sharpless epoxidation, was obtained using this procedure. Alcohol... 

In a new, stereospecific synthesis of functionalized butadienes, the elaborated norbornane (846 R = Me) undergoes a facile thermal retro-Diels-Alder reaction, and the intermediate cyclobutene (847) opens electrocyclically to a 2.5 1 mixture of E,E- and Z,Z-dienes. ... 

Dihydro-2H-l,2-oxazines from 1,1-nitrosohalides and dienes Stereospecific ring closure and synthesis... 

Tricarbonyliron diene complexes have been used in a simple stereospecific synthesis of insect pheromones. The basis of this synthesis relies on the Friedel-Crafts acylation of various diene complexes. The strategy is illustrated with a preparation of the pheromone (7) from the red bollworm moth (Scheme 29). 

They are used to prepare heterocycles such as 1,2-dihydropyridines, the pyrrolizidine alkaloid (+)-isoretronecanol and J-butyrolactone, and couple with allyIX to give 1,5-dienes. ot-EthoxybutenylSnBu is intermediate in the preparation of dihomoallyl ethers, and Me vSnCH2 allyl ethers provide for chiral transfer in the stereospecific synthesis of hydroxylated steroid side chains. The... 

A new general and stereospecific synthesis of c/s-l,2-divinyl systems has been achieved by flash vacuum pyrolysis of the 3-thiabicyclo[3.2.0]heptane 3,3-dioxide ring system. For example, the sulphone (61), prepared by photolysis of 2,5-dihydrothiophen 1,1-dioxide and maleic anhydride, eliminates sulphur dioxide to give the 1,5-diene (62) of greater than 99.9 /o c -geometry. 

The elimination of allylic sulphoxides to give (f jf )- ,3-dienes stereospecifically has been demonstrated by the synthesis of the pheromone of the codling moth (197) (Scheme 28), and the use of a stannyl group rather than silicon as a... 

A stereospecific synthesis of leukotriene (LTB )(48) from 2-deoxy-D-erythro-pentose has been described, outlined in Scheme 15. A key step in the synthesis utilized the discovery that furanose C-glycosides having a good leaving group at C-3 act as diene precursors, illustrated in the conversion of (49) to (50). (See also Vol.15,p.254). The authors have also shown that the... 

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