Trans substituted

Stereochemistry refers to chemistry in three dimensions Its foundations were laid by Jacobus van t Hoff and Joseph Achille Le Bel m 1874 Van t Hoff and Le Bel mde pendently proposed that the four bonds to carbon were directed toward the corners of a tetrahedron One consequence of a tetrahedral arrangement of bonds to carbon is that two compounds may be different because the arrangement of their atoms m space IS different Isomers that have the same constitution but differ m the spatial arrangement of their atoms are called stereoisomers We have already had considerable experience with certain types of stereoisomers—those involving cis and trans substitution patterns m alkenes and m cycloalkanes... 

A summary of the various axial and equatorial relationships among substituent groups in the different possible cis and trans substitution patterns for disubstituted cyclohexanes is given in Table 4.2. 

Although the yields of the above reactions are high and the procedure is simple186, there are some apparent disadvantages the selection of the sulfene substituents R1 and R2 is limited, depending on the availability of the sulfonyl chloride precursors the cycloaddition leads to a mixture of cis- and trans-substituted thietane dioxides the cycloaddition reaction is reversible202 and several further transformations are necessary if a dioxide without 3-lV-substituent is required. 

A further comparison of structures 41 and 42 shows that the main difference between the structures occurs near this same reactive bond. Structure 42 represents the most stable conformation expected of Dalanyl-Dalanine, where the amide is trans substituted and the nitrogen is oriented so that its lone pair of electrons may overlap with the tt orbitals of the carbonyl group. In... 

Up to 96% ee were obtained with trans-substituted oxazoline ligands of type 103. 

Although cyclopentanone 2 is a rather simple looking small molecule, the 3,4-trans-substituted architecture in a cyclopentanone ring provides significant complexity to this molecule. We devised two alternative routes for the preparation of 2. 

Depending on the Lewis acid used, cis- [139a] or trans-substituted products [139b-d] are accessible. When SnCL was employed at -78 °C as promoter, 2,3-cis-(3-lac-tones were obtained almost exclusively, whereas the ZnCl2-initiated reactions at r.t. afforded the corresponding trans-substituted compounds (Scheme 2.60). 

A combination of a Pd-catalyzed nucleophilic substitution by a phenol and a ring expansion was described by Ihara and coworkers [127] using cis- or trans-substituted propynylcyclobutanols 6/l-262a or 6/l-262b. The product ratio depends on the stereochemistry of the cyclobutanols and the acidity of the phenol 6/1-263. Thus, reaction of 6/l-262b with p-methoxyphenol 6/1-263 (X = pOMe) led exclu-... 

In 2001, Linder and Podlech studied the microwave-assisted decomposition of diazoketones derived from a-amino acids [340]. In the presence of imines, the initially formed ketene intermediates reacted spontaneously by [2+2] cydoaddition to form /3-lactams with a trans substitution pattern at positions C-3 and C-4 (Scheme 6.179) [340], In order to avoid the use of the high-boiling solvent 1,2-dichlorobenzene, most transformations were carried out in 1,2-dimethoxyethane under sealed-vessel conditions. Solvent-free protocols, in which the substrates were adsorbed onto an inorganic alumina support, led only to the corresponding homologated /3-amino acids. Evidently, traces of water present on the support trapped the intermediate ketene. 

The conversion of anomerically linked enol ethers 29 into either the cis- or trans-substituted pyranyl ketones with high diastereoselectivity and yield involves a Lewis acid-promoted O —> C rearrangement (Scheme 19) <00JCS(P1)2385>. Under similar conditions, homoallylic ethers 30 ring open and the oxonium ions then recyclise to new pyran derivatives 31. Whilst the product is a mixture of alkene isomers, catalytic hydrogenation occurs with excellent diastereoselectivity (Scheme 20) <00JCS(P1)1829>. 

The natural antipode of corynantheine (35, 155, 20/ ) has elegantly been prepared by Autrey and Scullard (168), starting from yohimbone (305), synthesized and resolved previously by Swan (169). Yohimbone (305) was converted to 18-formylyohimbone (306) and then through 307 to oxime 308. On reaction with thionyl chloride, 308 underwent a Beckmann fragmentation to the trans-substituted indolo[2,3-a]quinolizine 310, which after desulfurization and esterification resulted in the levorotatory methyl corynantheate (304). This product... 

Ene catalyst.1 FeCl3 is superior to ZnBr2 or alkylaluminum halides as a catalyst for ene cyclization of the chiral 1,7-diene 1, the Knoevenagel adduct from citronellal and dimethyl malonate. Thermal cyclization provides the 1,2-trans-substituted... 

The second example is an intermolecular crystal-state reaction. Cross-conjugated 1,5-disubstituted 1,4-dien-3-ones in solution undergo both cis-trans photoisomerization and photodimerization, yielding complex mixtures of products, including die all-trans-substituted cyclobutane 2 in the case of 1,5-diphenyl-1,4-pentadien-3-one. In contrast, dienones such as 3a in whose crystals adjacent molecules lie parallel and strongly overlapped react in the solid to give 3b as the sole photoproduct. This isomerically pure tricyclic diketone results, formally, from an eight-center dimerization. It is not formed in the reaction in solution, and could be prepared by other methods only with considerable difficulty (4). 

Complex 4b reacts with [M(CO)5(thf)] (M=Cr, W) to form initially complexes 12, which could be characterized by their NMR data, although a second substitution in the trans-position is preferred leading to the linear complexes 13a,b [17]. The driving force of the trans substitution was calculated via the corresponding isodesmic reaction and was found to be the formation of [M(C0)6] [17]. 

Furthermore the complexes 4 were reacted towards cationic Rh complexes (generated from [Rh(CO)2Cl]2 and T1PF6) to form twofold trans substituted products 14a,b (Eq. 13) [16]. Both the reaction with [M(CO)5(thf)] (M=Cr, W) as well as with [Rh(CO)2L2] reveal the tendency of the [(N3N)M=P]... 

The stereoselectivity can be rationalized by considering nonbonding interactions between R and the pyrrolidinyl substituents in TS 3, which favor TS 4 (Figure 7). Therefore, a decrease of the selectivity is observed for terminal or trans substituted oxiranes where R is a hydrogen. 

One method which is diagnostic of the diradical intermediate is the extent of retention of cis- and trans-substitution in the product from a cis- or tram-olefin. In a concerted process both bonds are formed concurrently, thereby prohibiting isomerization, whereas in the diradical mechanism the bond can rotate. 

Intramolecular alkylation has been used in the synthesis of the cyclopropane side chain of the marine sterols Glaucasterol95 and Petrosterol96. During the preparation of the latter the mesylate 1 was reacted with 1.0 equivalent of potassium-tcr -butoxide in tetrahydrofuran/ben-zene at 0°C to give the trans-substituted cyclopropane 2 in >70% yield. 

In a recent report, Shi et al. developed a valuable tool for the synthesis of 2,6-trans substituted morpholines by addition of water and alcohol to epoxy alkynes [109]. The procedure involved a domino three-membered ring opening, 6-exo-cycloisomerization, and subsequent intra-or intermolecular nucleophilic addition or a double-bond sequence. 

Cycloalkyl and secondary alkyl bromides react with N02 BF4 in pyridinium poly(hydrogen fluoride) solution to yield /J-fluorinated compounds in moderate to good yields. In the case of the cyclic starting materials like 1-bromocyclohexane only trans-substituted products are formed (see Table 22). 

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