Cyclopentanol trans-2-methyl

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 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. 

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)... 

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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