Ring opening with nitrogen nucleophile

The less reactive oxabicydo[2.2.1.]heptene 18 can also be ring-opened by nitrogen nucleophiles, such as N-methylaniline, to give the amino alcohol 19 as a single diastereoisomer in 93% yield and 95% ee (Scheme 10.9) [15]. As with alcohol nucleophiles, the [Rh -I]/PPF-tBu2 catalyst in solvent-less conditions was required for efficient ring-opening. 

The l-imino-lff-2-benzopyran (13) ring opens on treatment with nitrogen nucleophiles. Different modes of recyclisation are possible and (13) is therefore a source of a variety of -heterocycles <96AJC485>. 

As depicted in Scheme 11, ylides 39 derived from 4-methyl-[l,2,3]triazolo[l,5- ]pyridine react with Michael acceptors, which, upon nucleophilic attack at C3 and ring opening, lead to nucleophilic displacement of nitrogen. The intermediate diradical led to a mixture of compounds, including alkenes and a cyclobutane derivative when methyl acrylate was used, and the indolizine 40 with methyl propiolate as the electrophile <1998T9785>. Heating 4-methyl triazolopyridine with benzenesulfonyl chloride in acetone also confirmed decomposition via a radical pathway. 

In general, the reaction of unsaturated 5(4//)-oxazolones 497 with nitrogen nucleophiles effects ring opening to give the corresponding unsaturated acylamino amides 498 (Scheme 7.158). Depending on the nucleophile, for example, amines, hydrazines, oximes, and so on, the products obtained can be cyclized and this process allows the synthesis of a wide variety of new heterocyclic compounds. 

Reaction with Nitrogen Nucleophiles. The acid-catalyzed reaction of primary, secondary, and tertiary amines with ethyleneimine yields asymmetrically substituted ethylenediamines (71). Steric effects dominate basicity in the relative reactivity of various amines in the ring-opening reaction with ethyleneimine (72). The use of carbon dioxide as catalyst in the aminoethylation of aliphatic amines, for which a patent application has been filed (73), has two advantages. First, the corrosive salts produced when mineral acids are used as catalysts (74,75) are no longer formed, and second, the reaction proceeds with good yields under atmospheric pressure. 

Oxoniachrysenes 67 are simultaneously 2-benzopyrylium and 1-benzopyrylium salts, but maintain a distinct chemical behavior. 5-Oxoniachrysene salts 67 are interesting mainly as precursors of ben-zo[c]phenantridine derivatives 132, as mentioned in Section II,C,6. However, in contrast to 2-benzopyrylium salts (cf. Section III,C,4,a), compounds 67 react with nitrogen nucleophiles to form stable adducts 131 or products of anomalous ring-opening, namely a-naphthols 66 and esters 70 (77KGS1176). 

Nitrogen-based nucleophiles continue to remain popular in ring-opening reactions of aziridines. a-Substituted-a-methoxycarbonyl-V-nosylaziridines were opened with a variety of functionalized amines to provide access to enantiopure a,a -disubstituted (3-lactam scaffolds for ditopic peptidomimetics <07OL101>. A related intramolecular regioselective 3,Y-aziridine ring opening with an a-amino functionality was reported in the synthesis of... 

Aziridine and azetidine are stable, if volatile, members of the saturated nitrogen heterocycle family, and aziridine has some interesting chemistry of its own. Like pyrrolidine and piperidine, aziridine can be acylated by treatment with an acyl chloride, but the product is not stable. The ring opens with attack of chloride, a relatively poor nucleophile, and an open-chain secondary amide results. 

In contrast to HFPO, 2,2-bis(trifluoromethyl)oxirane (2) ring opens with oxygen, nitrogen, sulfur, and carbon nucleophiles at the less hindered carbon, yielding tertiary alcoholsWith diethylamine, for example, 2 affords an aminoalcohol in 83% yield. Oxirane 2 played an important role in the development of monomers from which to build highly transparent, yet readily alkali-soluble photoresist copolymers... 

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