Cyclic aminals 3+2 cycloaddition reactions

Oxidation of amines to nitrones.1 Secondary amines can be oxidized to nitrones by 30% H202 in the presence of a catalytic amount of Se02. The reaction is applicable to acyclic and cyclic amines. The products can be used without isolation in 1,3-dipolar cycloadditions. 

This work has since been extended to cyclobutyl isoxazolidine adducts (e.g., 86) from the cycloaddition of 87 to methylenecyclopropane (88) (Scheme 1.18) (124— 127). Thermolysis afforded a mixture of products, of which the bicyclic azepinone (89) predominated. Spirocyclic adducts were also prepared from an intramolecular reaction in the synthesis of cyclic amines (Scheme 1.72, Section 1.11.3). 

The mesoionic 2-T-cycloalkylamino-5-alkyl-l,3-dithiolium-4-thiolates 504 were prepared from 1,3-dithiocarbamoyl acid 503 in a retro-1,3-dipolar cycloaddition reaction. The acids were obtained by S-alkylation of triethylammonium 1,3-dithiocarbamates 501, easily synthesized from secondary cyclic amines 500 and CS2, with bromo acids 502 (Scheme 72) <1996PS75, 2002HC0593>. 

Nitrenes, the nitrogen analogs of carbenes have been introduced as a reactive group in photoaffinity labels for antibodies by Fleet et al. (1969). Nitrenes tend to be more selective in their reactions and possibly will provide fewer products than carbenes (but see also 6.2.3). The types of reaction that they can undergo (eq. 6.2, Knowles 1972) include insertions into C-H bonds to yield secondary amines, cycloadditions to double bonds to form cyclic 3-member imines and... 

Photochemical reactions of nitrogen-containing thiocarbonyl compounds ([2 + 2] cycloaddition to alkenes with formation of thietanes, transformations of thioimides to lactams and cyclic amines, cyclizations of thioamides) 03H(59)399. 

The catalytic [2 + 2 + 1]-cycloaddition reaction of two carbon—carbon multiple bonds with carbon monoxide has become a general synthetic method for five-membered cyclic carbonyl compounds. In particular, the Pauson-Khand reaction has been widely investigated and established as a powerful tool to synthesize cyclopentenone derivatives.110 Various kinds of transition metals, such as cobalt, titanium, ruthenium, rhodium, and iridium, are used as a catalyst for the Pauson-Khand reaction. The intramolecular Pauson-Khand reaction of the allyl propargyl ether and amine 91 produces the bicyclic ketones 93, which bear a heterocyclic ring as shown in Scheme 31. The reaction proceeds through formation of the bicyclic metallacyclopentene intermediate 92, which subsequently undergoes insertion of CO to give 93. 

An effective way for introduction of a variety of heterocyclic fragments in the position 7 of the fluoroquinolone skeleton is the methodology of 1,3-dipolar cycloaddition reactions [164-167]. Indeed, the reaction of 7-azido derivative of 6-fluoroquinolone 39 with enamines of cyclic ketones and norbomene proceeds rather smoothly with the formation of the corresponding exo-l,2,3-triazolines 40 which undergo the cationic rearrangements into amidines 41 or aminonorbomane 42 [164, 165]. 7-Azido derivatives 39 are capable of reacting with heterocyclic amines to form new 7- fluoroquinolones (Scheme 20) [168]. 

Cheng et al. [32a] and Rueping et al. [32b] independently described a direct catalytic asymmetric synthesis of cyclic aminals from 2-aminobenzamides 75 and aldehydes 3 using Brpnsted acid as a catalyst (Scheme 2.21). Phosphoric acids (5h or 5e) with bulky substituents on the 3,3 position had a high level of ability to promote the cycloaddition reaction with good stereoselectivity. 

Diaz-Ortiz described the cycloaddition of 4,6-dimethyl-l,2,3-triazine (105) with en-amines to give condensed pyridine systems [82]. These reactions were performed in a monomode reactor at a power of 270 W for 20 min at 15 °C. The reactions can also be performed with pyrrolidine, with cyclic ketones used as precursors of the enam-... 

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