Equatorial synthesis

The intramolecular cyclization of l-(4-bromobutyl)-3-methoxycarbonyl-l,4,5, 6-tetrahydropyridine (140) and l-(3-bromopropyl)-3-methoxycarbonyl-l,4,5,6-tetrahydropyridine (143) (89T5269) resulted in the synthesis of quinolizidine ring system 141 and indolizidine ring system 144 in 43% and 72% yields along with the reduced tetrahydropyridines 142 and 145 in 21% and 8% yields, respectively. All the cyclized products appeared to be (ran.s-fused indolizidines or quinolizidines. The (ran.s -fused simple indolizidines are known to be some 2.4 kcal mol more stable than the d.s-fused isomers (68TL6191). In the and-isomer the methoxycarbonyl substituent occupies an equatorial position. 

The bromide (5) failed to couple with dialkoxypyrimidines, even at elevated temperatures the failure is probably because of steric conditions imposed by the axially oriented C-4 p-nitrobenzoyloxyl group (see structure 5) this same group in the other halides (la, lb, 2a, 2b, 4a, and 4b) discussed in the foregoing is an equatorial substituent. Accordingly, the preparation of a differently constituted halide of 2-deoxy-D-Zt/xo-hexose is being investigated for the synthesis of pyrimidine nucleosides. 

The vibo or dl (124/35) quercitol (4) needed for the synthesis was prepared from rat/o-inositol (2) via the bromoquercitol (3) according to the method of McCasland and Horswill, (28). By acetonation, acetylation, deacetonation, and equatorial mesylation the mesyloxy derivative... 

C ( propyl) N phenylmtrone to N phenylmaleimide, 46, 96 semicarbazide hydrochloride to ami noacetone hydiochlonde, 46,1 tetraphenylcyclopentadienone to diphenyl acetylene, 46, 44 Alcohols, synthesis of equatorial, 47, 19 Aldehydes, aromatic, synthesis of, 47, 1 /3-chloro a,0 unsaturated, from ke tones and dimethylformamide-phosphorus oxy chloride, 46, 20 from alky 1 halides, 47, 97 from oxidation of alcohols with dimethyl sulfoxide, dicyclohexyl carbodumide, and pyndimum tnfluoroacetate, 47, 27 Alkylation, of 2 carbomethoxycyclo pentanone with benzyl chloride 45,7... 

Lewis acids, results in the formation of isopulegol (43) with greater than 98% diastereoselectivity isopulegol (43), wherein all of the ring substituents are equatorially oriented, arises naturally from a chairlike transition state structure in which the C-3 methyl group, the coordinated C-l aldehyde carbonyl, and the A6,7 double bond are all equatorial (see 48). A low-temperature crystallization raises the chemical and enantiomeric purity of isopulegol (43) close to 100%. Finally, hydrogenation of the double bond in 43 completes the synthesis of (-)-menthol (1). 

The synthesis of the 2-acyloxathianes 3 makes use of the fact that for stereoelectronic reasons1, electrophilic attack on conformationally locked 2-lithiated oxathianes 1 leads exclusively to equatorially substituted products 2. A subsequent oxidation step completes the synthesis. 

The reactions of allylboronates 1 (R = H or CH3) may proceed either by way of transition state 3, in which the a-substituent X adopts an axial position, or 4 in which X occupies an equatorial position. These two pathways are easily distinguished since 3 provides 7 with a Z-olefin, whereas 4 provides 8 with an E-olefinic linkage. There is also a second fundamental stereochemical difference between these two transition states 7 and 8 are heterochirally related from reactions in which 1 is not racemic. That is, 7 and 8 arc enantiomers once the stereochemistry-associated with the double bond is destroyed. Thus, the selectivity for reaction by way of 3 in preference to 4, or via 6 in preference to 5 in reactions of a-subsliluted (Z)-2-butenylboronate 2, is an important factor that determines the suitability of these reagents for applications in enantioselective or acyclic diastereoselective synthesis. 

Synthesis of this compound from a 15N labelled source revealed that the i4N and 15N were equally distributed between the apical bent nitrosyl (NO-) and equatorial linear nitrosyl (NO+) ... 

Landry, M. R., Barber, R. T., Bidigare, R. R. et al. (1997). Iron and grazing constraints on primary production in the central equatorial Pacific and EqPac synthesis. Limnol. Oceanogr. 42,405-418. 

Chemo- and stereoselective reduction of (56) to (55) is achieved In highest yield by sodium borohydride in ethanol. The isolated ketone is reduced more rapidly than the enone and (55) is the equatorial alcohol. Protection moves the double bond out of conjugation and even the distant OH group in (54) successfully controls the stereochemistry of the Simmons-Smith reaction. No cyclopropanation occurred unless the OH group was there. Synthesis ... 

The treatment of gold(III) complexes with the rigid bidentate ligand phen allows the synthesis of pseudo-pentacoordinate gold(III) derivatives. This is the case of [Au(dmp)(phen)PPh3](BF4)2 (288) (dmp = 2-(dimethylaminomethyl)phenyl)1699 or [AuCl(C4Ph4)(phen)].16 2 The donor atoms of the phenanthroline ligand occupy one equatorial and the axial position of a square pyramid with distances 2.154(8)A and 2.627(10)A in (288). 

Since the steric requirement of the /erf-butyl group was known to be much larger than that of the isopropyl group, as exemplified by the free energy difference involved in the axial-equatorial equilibrium of substituted cyclohexanes56), 2,7-di-terf-butylthiepin derivatives seemed to be more promising candidates for the synthesis. 

Phenylthio)nitroalkenes are also excellent intermediates for the synthesis of other heterocyclic ring systems. For example, tetrahydropyran carboxylic acid derivatives are formed by the intramolecular addition of oxygen nucleophile to l-(phenylthio)nitroalkene predominantly as the m-isomer (9.1 1) (see Eq. 4.40). The reaction may proceed via the chair-like transition state with two pseudo-equatorial substituents.50... 

The key step in the synthesis of the branched sugars presented in Scheme 7.2 is a Kornblum reaction of the nitropyranose. A mixture of anomers is obtained in the reaction of nitrofuranose, but the reaction with nitropyranose proceeds diastereoselectively to give a single product with an equatorially oriented side chain. 

The synthesis, aggregation behavior, and catalytic activity of Rh complexes of Xantphos derivatives (129) with surface-active pendant groups have been described.416 The complex [HRh(CO)(TPPTS)3] was used as a catalyst precursor in the hydroformylation of 1-butene, 1-octene, and styrene under biphasic reaction conditions 417 The two-phase hydroformylation of buta-1,3-diene with [HRh(CO)(TPPTS)3], with excess TPPPS, gives high yields of C5-monoaldehydes.418 The coordination behavior of the catalytic species HRh(130)(CO)2] was studied by HP NMR spectroscopy which showed the desired bis-equatorial coordination of the ligand to the rhodium center.419... 

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