Trans-2- cyclopentanol

MeON=CH(CH2)3CHO with BusSnH and AIBN, for example led to trans-2-(methoxyamino)cyclopentanol in good yield.Addition of radical to the C=N unit of R—C=N—SPh or R—C=N—OBz led to cyclic imines. Radical addition to... 

Figure 11.1 The hydroboration-oxidation of 1-methylcyclopentene. The first reaction is a syn addition of borane. (In this illustration we have shown the boron and hydrogen both entering from the bottom side of 1-methylcyclopentene. The reaction also takes place from the top side at an equal rate to produce the enantiomer.) In the second reaction the boron atom is replaced by a hydroxyl group with retention of configuration. The product is a trans compound (trans-2-methyl-cyclopentanol), and the overall result is the syn addition of -H and -OH.

The oxidation of cyclic 2-amino alcohols has been studied.88 In the 2-amino-cyclopentanol series, the ds form was oxidized four times as fast as the trans but, in the 2-amino-cyclohexanol series, the ds form reacted slightly more slowly than did the tram. 

However, the reactions of mono substituted cyclopentanone sometimes becomes so much stereodirected that a mixture of cis and trans isomers is obtained. For example the reduction of 2-alkyl cyclopentanone by LiAlH4 gives a mixture of cis-trans isomeric alkyl cyclopentanols. 

Finch et al. described the separation of cis- and trans-2-hydroxymethyl-1-cyclopentanol, based on the fact that the trans compound did not undergo ring closure to 1,3-dioxane (75JOC206). 

Some conversion into the anhydrovitamin (112) occurs during silica gel t.l.c. of retinyl palmitate in non-polar solvents. Some new colour reactions of vitamin A are reported to be better than the Carr-Price reaction. The kinetics and mechanism of acid-catalysed isomerization of retinyl acetate into the trans-retro-derivative (113) have been studied. Oppenauer oxidation of kitol (39) results in specific cyclopentanol-cyclopentanone oxidation. ... 

Compounds such as y-dimethylvalerophenones (8) and P-ethoxypropiophenone (9), which lack y— H, produce exclusively cyclopentanol 10 and tetrahydrofuranol 11 derivatives, respectively, albeit in low quantum yields (Scheme 8.2). With benzene as solvent, the diastereomeric ratio for 11 was 5 1 (trans/cis), but was 1 1 in acetonitrile. The easy 1,5-H-transfer in these acyclic ketones was rationalized as involving a torsion-free, chair-like six-membered transition state. 

The synthesis of bicyclic cyclopentanols (46) via photoreductive cyclization of 5,8-unsaturated ketones (45) has been realized by Belotti et al. using hexamethylphosporic triamide (HMPA) or triethylamine (TEA) as electron donor [46]. The photocyclization proceeded remarkably efficient when HMPA was used as donor and solvent (Sch. 24). Furthermore, only one stereoisomer was obtained carrying methyl and hydroxy groups in trans-configuration. In contrast, the yields for cyclization dropped significantly when TEA in a polar solvent such as acetonitrile was used. As an example, the yield for 46 (n= 1) decreased from 81% in HMPA to 50% in TEA/ MeCN. 

The cases of polysubstituted cyclic systems are obviously more complex due to the existence of a number of possible configurational isomers. A simple cis-trans nomenclature is obviously not sufficient here, so the IUPAC recommends to designate the various diastereoisomers by choosing a reference substituent (the lowest numbered substituent, designated r) and defining its cis or trans (c or t) relationship to all other substituents (see [60]). Thus, the three diastereoisomers of LIII are c-2,c-5-dimethyl-, f-2, f-5-dimethyl and c-2, t-5-dimethyl-r-1 -cyclopentanol. 

Problem 9.23 Starting with cyclopentanol, show the reactions and reagents needed to prepare (a) cyclopentene, (b) 3-bromocyc opentane, (c) 1,3-cycIopentadiene, (d) trans-1,2-dibromocyclopentane, (e) cyclopentane. ... 

In contrast to the results of Kovar et at., McCasland and Smith found that ci5-2-amino-cyclopentanol is oxidised more rapidly than the trans- isomer. Bar-low et al. determined the second-order rate coefficients at pH 4.0 (acetate buffer) and 25 °C for a series of amino sugars derived from the eight isomeric methyl-4,6-0-benzylidene-a-D-glycosides (VII)... 

Radical cyclization is not limited to reaction with a C=C unit (see 15-29 and 15-30), and reactions with both C=N and C=0 moieties are known. Reaction of MeON=CH(CH2)3CHO with Bu3SnH and AIBN, for example, led to trans-2-(methoxyamino)cyclopentanol in good yield.Conjugated ketones add to aldehyde via the p-carbon under radical conditions (2 equivalents of Bu3SnH and 0.1 equivalent of CuCl) to give a p-hydroxy ketone.Addition of radical to the C=N unit of R C=N SPh ° or R—C=N—led to cyclic imines. Radical addition to simple imines leads to aminocycloalkenes. Radical also add to the carbonyl unit of phenylthio esters to give cyclic ketones. 

Cyclohexylmethylpropiolaldehyde diethyl acetal, 39, 60 1,2-Cyclononanedione, 36, 78 Cyclopentadiene, 32, 41 36, 32, 35 Cyclopentanecarboxylic acid, METHYL ESTER, 39, 37 Cyclopentanol, 2-chloro-, trans-,... 

As can be seen in Figure 4, the hydroboration-oxidation of 1-methylcyclopentene produces only the trans-2-methyl-cyclopentanol with a yield of 86%.45 This result implies that the boron atom and the hydrogen atom are added to the double bond simultaneously on a syn mechanism.46 A concerted mechanism is invoked for these additions - it is shown in Figure 5.1... 

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