Use of the diazoalkane–thione reaction in the synthesis of a vinyltrimethylenemethane precursor

Abstract

Previous studies have shown that the reaction of diazoalkanes with 3,5-dihydro-3,3,5,5-tetramethylpyrazole-4-thione ( 6 ) provide a flexible route for the synthesis of precursors to trimethylenemethane (TM M) (1 ) and tetramethylene-ethane (TM E) (2) biradicals. We now show that this route can be adapted for the synthesis of a precursor to another type of non-Kekul6 polyene, a vinyl-TMM biradical (3). The thermal isomerisation of 1 -(2,4-dimethylpent-l -en-3-ylidene) -2,2,3,3-tetramethylcyclopropane ( 2 7 ) to 4-isopropyl-3-isopropylidene-2,5-dimethylhexa-1,4-diene (I 1) which involves a vinyl-TMM intermediate (3-isopropyl-4-isopropylidene-2,5-dimethylhex-2-ene-I ,5-diyl) was shown by deuterium labelling to involve a 1,6-hydrogen shift. It is suggested that such sigmatropic rearrangements of non-Kekule polyenes may involve orbital symmetry control. Related examples are discussed. Two reactions discovered incidentally in the course of this work are of some interest, one involving the synthesis of an allylic amine through the thermal rearrangement of an aziridine (2-isopropyl-3,3-aziridine) (1 6) and the other the formation of an oxathiole ( 2 0 ) through the reaction of a thione ( 6 ) and an x-diazo ketone (3-diazo-4-methylpentan-2-one) (1 8 ) .Trimethqlenemethane (TMM) (1) '.' has 4 n electrons and is isomeric with butadiene. Since it is not possible to write a structure for T M M in which all 4 n electrons are paired, it is knobcn as a non-Kekule polyene' and as no 'closed shell' structure can be written. it seems reasonable to suppose that TMM will behave as a biradical. This simple expectation is confirmed both by experiment '.' and by molecular orbital calculations.3 TMM is in f x t the simplest member of a whole famil! of non-Kekule polyenes. There are two non-Kekule polyenes which have 6 n electrons and which are isomeric with hexatriene [tetramethylene-ethane T M E (2), and vinyl-TMM (311 and seven non-Kekule polyenes which have 8 n electrons .x.which are isomeric with octatetraene. In previous papers in this series we have shown that precursors to TMM 4.s and TME biradicals [for example compound (9)] could be elaborated from the thione (6). In the present paper we show that this same thione can be used to make a precursor to the less well knoivn type of 6 n electron non-Kekule polyene. a ~. i n~. l -TMM.7 The particular vinyl-TMM biradical which we wanted to study was 3-isopropyl-4-isopropylidene-2.5-dimethylhex-2-ene-1 S-diyl (4). Our interest in this particular biradical arose since it may well be an intermediate in the thermal isomerisation of the spiropentane (10) to the triene ( l l ) . 6Retrosynthetic analysis (Scheme 1 ) suggests that the vinyl-TMM (4) could be derived from the dihydropyrazole (5), which it should be possible to obtain from the addition reaction between the thione ( 6 ) and the diazoalkane (7).4-6 The initial objective was therefore the preparation of a precursor to the diazoalkane. the allylic amine (8). There are not many general routes to allylic amities but the synthesis of com...

Synthesis of Highly Functionalized 1,3-Oxathioles via an Unusual [4+1] Annulation of α,α'-Dioxothione with 1,2-Diaza-1,3-dienes

“…The 13 C NMR spectrum showed six C-sp 2 signals (δ = 168. 5, 162.4, 158.8, 157.3, 142.2 and 101.8 ppm) and one C-sp 3 signal at δ = 96.7 ppm, consistent with the presence of a oxathiole ring, 18,19 The presence of one sp 3 -hybridized carbon atom on the heterocyclic skeleton together with both an electrophilic ester group and a nucleophilic hydrazone residue at the C2-position make these compounds attractive for subsequent modification. Therefore, the possibility of derivatization to other α-oxathiolo-related structures was explored.…”

“…The13 C NMR spectrum showed six C-sp 2 signals (δ = 168.5, 162.4, 158.8, 157.3, 142.2 and 101.8 ppm) and one C-sp 3 signal at δ = 96.7 ppm, consistent with the presence of a oxathiole ring,18,19 and the IR spectrum exhibited a…”

Efficient Anti‐Markovnikov‐Selective Catalysts for Intermolecular Alkyne Hydroamination: Recent Advances and Synthetic Applications

“…[52] Notably, such substituted allylamines are desirable synthetic building blocks. [52,53] For example, benzhydrylamine can be used as a nitrogen source and an alkyne can furnish the α-carbon fragment. Hydroamination of hex-1-yne with benzhydrylamine affords imine 23.…”

Synthesis of Methylene- and Alkylidenecyclopropane Derivatives

“…Several alkyl-substituted MCPs and ACPs were synthesized by this method. − In one case the methylene pyrazoline 106 was obtained from a pyrazolidinone by Wittig olefination . In another single case the pyrazoline 107 was obtained by reaction of a TMM diradical with diazodicarboxylate followed by decarboxylation and oxidation.…”