The Hetarynes

Abstract

Dedicated to Professor Fritz Micheel on the occasion of his 65th birthdayInvestigations carriedout during the last six years have shown that, as in the case of benzene, an extra bond can be introduced into heteroaromatic rings. Since this possibility does not appear to be confined to exceprional cases, the heterocyclic arynes (hetarynes) promise a much wider variety than the carbocyclic arynes. Hetarynes occur mainly as intermediates in nucleophilic substitutions on halogenated heterocyclic compounds. Since the replacement of a C H group in dehydrobenzene by a nitrogen atom and the condensation of benzene rings have stabilizing effects, the stability of hetarynes is expected to increase with the number of N atoms and with the number of condensed aromatic rings.

Polarized ketene dithioacetals. Part 26. Studies on base-catalysed rearrangements of 3,3-bis(alkylthio)-2-methyl-1-arylprop-2-en-1-ones and 3,3-bis(methylthio)-2-benzyl-1-phenylprop-2-en-1-one

“…bands at 1 650 and 1 655 cm-", which were assigned to the carbonyl groups of the 2 and E isomers, respectively. The structure of compound (14) was further confirmed by treating (14) with hydrazine hydrate, when the pyrazole (18) (Scheme 5) was formed in 57% yield: the structure of (18) was confirmed by its analytical and spectral data (Experimental section). spectrum (Figure) showed two singlets at 6 1.60 and 1.80 (total 3 H), which were assigned to the methylene SMe protons of the 2 and E isomers (1 : 3) respectively.…”

“…The products (14) and (15) are the expected rearranged products from the dimethyl dithioacetal(l3), while compounds (16) and (17) are formed by oxidative cleavage of the intermediate carbanions involved. Further experiments on (1 3) under similar reaction conditions for longer periods (8 h) yielded only (16) and (17) in 10 and 70% yields respectively, indicating the possible conversion of (14) and (15) into (16) and (17) respectively.…”

Formal Fusion of a Pyrrole Ring onto 2-Pyridyl and 2-Pyrimidyl Cations: One-Step Gas-Phase Synthesis of Indolizine and Its Derivatives

“…[1,17] Not surprisingly therefore, these ªprotonated moleculesº react with 1,3-dienes predominantly by proton transfer (as rationalized for 6 in Scheme 3), thus displaying an aromatic carbocation-like behavior similar to that of the phenyl cation. [18] Scheme 3.…”

“…This novel and efficient gas-phase reaction occurs through several steps: initial polar [4 2 ] cycloaddition, ring-opening, [1,4-H] shift, and recyclization to result in the contraction from a six-to a five-membered ring; and dissociation by the loss of a methyl radical. The 2-pyridyl cation (1) gives the ionized pyrrolo[1,2-a]pyridines (indolizines), while the 2-pyrimidyl cation (2) gives ionized pyrrolo[1,2-a]pyrimidines.…”

“…The simplest ortho-hetarynium ion, [1] the mesomeric 2-pyridyl cation (1), and its N-analogue, the 2-pyrimidyl cation (2), are isoeletronic with ortho-benzyne, the simplest and most common aryne, and like ortho-benzyne, [2] they both participate as key and short-lived intermediates in several reactions in the condensed phase. [3] The fully occupied sp 2 orbital of the ring nitrogen(s) and the empty sp 2 orbital of the neighboring carbon atom of 1 and 2 overlap extensively, which results in extra resonance stabilization of 18 ± 28 kcal mol À1 (as compared to the meta and para isomers); hence the ortho-hetarynium ion structures 1' and 2' largely dominate.…”