Nitrogen electrophiles

Reactivity of A-4-thiazoline-2-thiones and derivatives involves four main possibilities nucleophilic reactivity of exocyclic sulfur atom or ring nitrogen, electrophilic reactivity of carbon 2 and electrophilic substitution on carbon 5. 

Thermal and photochemical reactions formally involving no other species Electrophilic attack at ring oxygen Electrophilic attack at ring nitrogen Electrophilic attack at ring carbon... 

A similar synthesis of mechanistic interest rather than preparative value involves the thermal reaction of dimethyl 2,5-bisdiazo-3,4-diketoadipate (89, Scheme 23) with benzofuran (91)." The presumed intermediate is the pyrone cation 90 produced from the adipate 89 by the Wolff rearrangement, cyclization, and loss of nitrogen. Electrophilic substitution then affords the benzofuran 92, which can be isolated. Ring opening and cyclization of the resultant ketene 93 then affords the dibenzofuran 94 in poor (0.4%) yield. 

Thermal and Photochemical Reactions Electrophilic Attack at Nitrogen Electrophilic Attack at Carbon Nucleophilic Attack at Carbon Nucleophilic Attack at Hydrogen Reduction Oxidation... 

In contrast to stereoselective C-C bond-forming reactions, the related electrophilic animation of chiral carbon nucleophiles is a recent conceptual advance in the repertoire of synthetic methodology. The problem is the correct choice of the nucleophile, and of the most efficient nitrogen electrophile. The chemistry of useful reagents such as sulfonyl azides 3 and chloro nitroso alkanes 5 was excellently reviewed in 1995 [Id]. This chapter outlines a collection of the major reports that have appeared in the field of stereoselective electrophilic animation using sulfonyloxy-carbamates 6 and azodicarboxylates 4. 

Examples of nitrogen electrophiles which participate in reversed cohalogenation are nitryl halides453"456 and nitrosyl halides457,458. 

The very successful application of organometallic compounds in stereoselective C-C bondforming reactions over the last 20 years has raised the question as to whether C-N bonds could also be formed in a stereoselective way via a related protocol. Standard methods have been evaluated for the preparation of a vast number of (chiral) carbon nucleophiles RM. The problem, however, is the right choice of nitrogen electrophile which compounds are best suited for this purpose ... 

The chemistry of nitrogen electrophiles R R2NX (I) was excellently summarized in 1989Ia. Recent studies in the field of stereoselective electrophilic amination, however, have shown that azidation with sulfonyl azides III, reactions with di-tert-butyl azodicarboxylate (II) and reactions with 1-chloro-l-nitroso reagents IV, are superior to the previously mentioned nitrogen electrophiles. 

The procedure outlined here160,11 closely resembles the methodology detailed in Section 7.1.1.1., except for the choice of nitrogen electrophile used, which in this case is the commercially available di-tert-butyl azodicarboxylate (DBAD). The reaction of the lithium derivatives of N-acyloxazolidinones 1 with DBAD affords diastereomerically pure (>300 1) hydrazines 2 in yields exceeding 90%1 a. 

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