Camphor, enamines

Similarly, camphor enamines were hydrogenated to give preferentially the exo amines181. 

The reduction of camphor enamines by the same method has been found to be highly selective, leading to the endo isomer as the predominant product (85-87%)204 (Scheme 136). The lack of solvent effect and the incorporation of up to 3 deuterium atoms when using DCOOD, are in favour of a two-step mechanism. This would involve reversible protonation of the / -carbon atom with formation of the iminium ion, followed by irreversible transfer of hydride from the formate ion to this ion. 

Fig. 3. Response surface showing the variation in yield in the reduction of camphor enamine...

Several methods for asymmetric C —C bond formation have been developed based on the 1,4-addition of chiral nonracemic azaenolates derived from optically active imines or enamines. These methods are closely related to the Enders and Schollkopf procedures. A notable advantage of all these methods is the ready removal of the auxiliary group. Two types of auxiliaries were generally used to prepare the Michael donor chiral ketones, such as camphor or 2-hydroxy-3-pinanone chiral amines, in particular 1-phenylethanamine, and amino alcohol and amino acid derivatives. 

Enamines can be reduced to the corresponding saturated amines by treatment with formic acid. A very simple experimental procedure can be used in which formic acid is added to the neat enamine at such a rate that foaming due to evolution of carbon dioxide can be kept under control. The reduction of the morpholine enamine from camphor was studied in a two-level factorial design in order to determine whether or not an excess of formic acid should be used and at which temperature the reaction should be run. 

Selection of test items so that they are as dissimilar a possible to each other is accomplished by choosing items which are projected far from each other and on the periphery of the plot. Such designs are useful for answering the question of whether or not the properties have an influence. A maximum spread design wa used to determine whether modification of the solvent would increase the endo/exo stereoselectivity in the reduction of an enamine from camphor. The answer was negative [17 a],... 

According to this mechanism, the enamine form is fluorinated by A-fluorobis(tri-fluoromethynesulfonyl)amine. The difficulty of camphor imine to undergo tautomerism explains the lack of reactivity observed with this substrate. ... 

Molecular sieves, 55, 130, 316-317 Molybdenum carbonyl, 317 Monensin, 136, 137, 173 Monoisopinocampheylboranc, 317 Monothioacetals, 6-7 Monotrimethylsilyl acetamide, 113 Morpholine, 138, 139 Morpholine-Camphoric acid, 317-318 Morpholine enamines, 319 N-Morpholinomethyldiphenylphosphine... 

The next step was to study if even more hindered ketones, like camphor, could be converted to enamine by an excess of reagents. Formation of enamines from camphor by traditional methods affords very poor yields. By the present method, molar scale synthesis from camphor afforded yields of enamines in the range 78-81 %.[19]... 

The reduction of the morpholine enamine from camphor by the reaction with formic acid was discussed in Chapter 5. In the example below, this reaction was applied to the reduction of the corresponding pyrrolidine enamine. The reaction was conducted without any solvent present, i.e. by adding formic acid dropwise to the hot enamine, and afforded an almost quantitative conversion to the corresponding bornyl pyrrolidine. However, the reaction was not stereoselective and a mixture of endo and exo isomers was formed. The proportions were endo isomer (85 %), exo isomer (15 %). This was regarded as a promising result. 

The d/-ketone (5) did not form an enamine readily but was resolved by dissolving 7.7 g. in hot absolute ethanol (45 ml.) and adding 6.4 g. of pyrrolidine perchlorate3 and 2 drops of pyrrolidine. The enamine perchlorate that crystallized was collected and treated with potassium d-camphor-10-sulfonate in absolute methanol. Crystallization then gave enantiomeric salts and from them the (+) and (—) ketones were recovered. 

The asymmetric 3 + 2-cycloaddition of cyclic azomethine ylides with Oppolzer s acryloyl camphor sultam has been used for the construction of X-azabicyclo[7M.2.1] alkenes in optically pure form. The non-stereospeciflc 1,3-dipolar cycloaddition of electron-poor azomethine ylides and electron-rich enamines proceeds by a two-step mechanism via zwitterionic intermediates. The 1,3-dipolar cycloaddition of 4,6-diazaphenanthrene 6-phenacylide with a variety of dienophiles readily produces the fused heterocycles tetrahydrobenzo[/]pyrrolo[l,2-/z][l,7]naphthyridines. Sequential... 

---