Nucleophilic substitution reactions by electron transfer

The amount of research activity concerning alpha-methylene-gamma-butyrolactones and alpha-alkylidene-gamma-butyrolactones has increased dramatically in recent years. This Review summarizes the structural types, biological activities, and biosynthesis of these compounds, concentrating on publications from the past 10 years. Traditional approaches to alpha-methylene-gamma-butyrolactones and alpha-alkylidene-gamma-butyrolactones are then reviewed together with novel approaches, including those from our own research group, reported more recently.

The Renaissance of α‐Methylene‐γ‐butyrolactones: New Synthetic Approaches

Some New Nazarov Chemistry

Data on the synthetic routes to substituted 1,2,3-triazoles, including those containing functional groups, based on cyclisation of various nitrogen compounds published during the last 15 years are described. Examples of using new triazole derivatives in agrochemistry, medicine and engineering are given.

https://iopscience.iop.org/article/10.1070/RC2005v074n04ABEH000893/pdf

1,2,3-Triazole and its derivatives. Development of methods for the formation of the triazole ring

We describe a novel procedure for the straightforward synthesis of seven-membered carbocycles via free-radical chemistry, based on titanocene(III)-catalyzed 7-endo-dig and 7-endo-trig cyclizations. This procedure has proved to be useful for the chemical preparation of terpenoids with different skeletons containing cycloheptane rings, including the first total syntheses of dauca-4(11),8-diene (2), barekoxide (3), authentic laukarlaol (81), and a valparane diterpenoid (72), as well as a substantially improved synthesis of karahanaenone (1). We also provide theoretical and experimental evidence in support of a plausible mechanism, which may rationalize the preference for the unusual 7-endo cyclization mode shown by radicals with substitution patterns characteristic of the linalyl, nerolidyl, and geranyl linalyl systems. In light of these chemical findings, we discuss the potential involvement of radical cyclizations in the biosynthesis of some terpenoids containing seven-membered carbocycles.

7-endo radical cyclizations catalyzed by titanocene(III). Straightforward synthesis of terpenoids with seven-membered carbocycles.

β-Bromopropargyl ethers 2a-h, 11, and 12 or allyl propargyl ethers 8d-h are easily isomerized with potassium tert-butoxide (KO-t-Bu) into the corresponding allenyl derivatives 3a-h, 13, 14, and 9d-h. These compounds afford α-methylene-γ-butyrolactones 7a-h, 25, and 26 by application of the sequence halogenation/dehydrohalogenation/homolytic carbocyclization. Starting from methyl vinyl ketone 1i, similar transformations lead to botryodiplodin (27) or ethoxybotryodiplodin (28)

Allenyl ethers as precursors of .alpha.-methylene-.gamma.-butyrolactones and botryodiplodin derivatives

Application of the sequence halogenation/dehydrohalogenation/isomerization to alkenes 1a-g affords allenyl allylic ethers 5a-g. Thermal isomerizations of 5a,d,e proceed by Claisen rearrangement, while 5b,c,f,g are transformed by alternate modes of [2+2]cycloaddition involving biradical intermediates of type 19 to polycyclic structures; the variations in these thermal isomerizations are mainly a function of ring size

Allenyl allylic ethers: synthesis and thermal rearrangements

Thermal cyclization of 1-azido-2-penten-4-ynes and 4-azido-2-butenenitriles led to 6H-pyrrolo [1,2-c][1,2,3]triazoles and 5H-pyrrolo [1,2-d]tetrazoles, respectively, in good yields. Upon treatment with methyllithium these heterocyclic compounds gave the corresponding aromatic anions which can be alkylated with methyl iodide or acylated with ethyl chloroformate

Jean Pierre Dulcere

Papers

Allenyl ethers as precursors of .alpha.-methylene-.gamma.-butyrolactones and botryodiplodin derivatives

Allenyl allylic ethers: synthesis and thermal rearrangements

Synthesis of 6H-pyrrolo[1,2-c][1,2,3]triazoles and 5H-pyrrolo[1,2-d]tetrazoles: alkylation and acylation of the monoanions

Acylation of alkenes generated in situ by hydride transfer from isoalkanes. Synthesis of pentalenones, hydrindenones, and cyclopentenones

Facile and selective epoxidation with the hydrogen peroxide/Vilsmeier reagent system