Amidines in Organic Synthesis

Graduate School of Pharmaceutical Sciences, Chiba University, 1-33 Yayoi, Inage, Chiba 263-8522, Japan 

On the other hand, in the 1960s sterically hindered bicyclic amidines, 1,8-diazabicylo [5.4.0]undec-7-ene (DBU) (1) and l,5-diazabicylo[4.3.0]non-5-ene (DBN) (2), were introduced as useful dehydrohalogenation reagents in the synthesis of vitamin A. Treatment 

Superbases for Organic Synthesis Guanidines, Amidines, Phosphazenes and Related Organocatalysts Edited by Tsutomu Ishikawa 2009 John Wiley Sons, Ltd. ISBN 978-0-470-51800-7 

These amidines have been extensively applied to dehydrohalogenation in organic synthesis and in some cases DBU (1) is more effective than DBN (2) [5]. A double bond can be also introduced into organic molecules by elimination of sulfonate ester instead of the halogen atom (i.e. dehydrosulfonation in addition to dehydrohalogenation). Furthermore, these amidines can be applied to the Wittig reaction [6], aldol condensation [6], 1,3-allyl rearrangement [7] and epimerization of the (3-lactam skeleton (at Ce of the penicillic acid derivatives). Sterically hindered phenols (e.g. 2,6-di(ferf-butyl)-4-fluorophenol) are (9-acetylated with DBU (1), which is superior to sodium hydroxide in the synthesis [8]. 

The efficiencies of DBU (1) and DBN (2) as sterically hindered (non-nucleophilic) and strong organobase catalysts have been widely demonstrated [5]. However, Reed et al. [12] claimed that they could behave as strong nucleophiles in the reaction of chlorobis (diisopropylamino)phosphane and DBU (1) or DBN (2). 

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Review Bicyclic amidines as reagents in organic synthesis." ... 

Applications in organic synthesis of the iminoacylation reaction of oximes have recently been found at kinetically labile Zn11- or Con-oxime systems. The former catalyzes the hydrolysis of nitriles to carboxamides (23)37 and the Co11 system catalyzes the conversion of nitriles into amidines (24) (also involving C N bond formation upon reaction with ammonia, formed from competitive hydrolysis of the nitrile).110... 

Numerous applications have been found for the uses of imidazole derivatives as ionic liquids and A -heterocyclic carbenes and their use in organic chemistry has been well discussed in books or reviews. Thus, in this chapter, the use of non-heteroaromatic amidine compounds as functional tools in asymmetric synthesis and the related chemistry after presentation of the preparation method of amidines will mainly be discussed. 

C. Laurence and J.-F. Gal, Lewis Basicity and Affinity Scales Data and Measurement, John WUey Sons, New York, 2010, is an outstanding reference with respect to both tabulated data and discussion of methodology. G. GUh and P. GUh, The Nature of the Hydrogen Bond, Oxford University Press, New York, 2009, provides an in-depth discussion of this topic. For an excellent review of superbases Superbases for Organic Synthesis Guanidines, Amidines, and Phosphazenes and Related Organocatalysts, Ishikawa, T., eds., Wdey, New York, 2009. 

Scandium catalysts were often used in combinatorial organic synthesis. For library production of a-amino amidines, multicomponent reactions involving aldehydes, amines, and isonitriles (3CC Ugi condensation) were developed using Sc(OTf)3 as catalyst (Scheme 12.28). A set of amino amidines was synthesized by this method in good to excellent yields [63]. 

The oxidative C-N bond formation by hypervalent iodine(III) species continued to be an efficient organic tool in the synthesis of various benzofused heterocycles. A catalytic amount of iodine(III) species was sufficient to drive tire reaction to yield various N-substituted benzimidazoles 159 (Scheme 38). Active I(IIl) was produced by the oxidation of a catalytic amount of iodobenzene using co-oxidant m-CPBA. The I(III) species reacted with amidines 158 to generate... 

The first examples of the 1,2,3,5-dithiadiazolium cation (38) were obtained in 1977 from the treatment of organic nitriles with (NSC1)3. This reaction has subsequently been shown to proceed by the intermediate formation of S,S -dichlorodithiatriazines (39). Another route to (38) involves the cyclocondensation of trisilylated amidines with sulfur dichloride (equation 20). This method is readily extended to the synthesis of multidithiadiazolium cations, for example, 1,3,5-C6H3(CNSSN)32+.i 3... 

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