1,7-Electrocyclisation and carbene reactions of o-alkenylaryldiazoalkanes: the effect of alkene configuration on the mode of reaction

Abstract

The 1,7-8.rc-electron electrocyclisation of o-alkenylaryldiazoalkanes (1 ) to give 1 H-2,3-benzodiazepines (3) takes place readily for substrates with a cis-hydrogen atom at the cyclisation site, but is blocked b y phenyl or methyl groups at that position. Such compounds react only via loss of nitrogen, the former, e.g. (18), to give naphtho[a]cycloheptenes (20) b y a n e w intramolecular carbene reaction, and the latter to give carbene 'dimers', azines, products of solvent insertion, and in one case an indene (37). The blocking effect of cis-methyl and -phenyl groups is attributed to steric hindrance in a helical transition state (42) for the 1,7-electrocyclisation. The results are also discussed in relation t o the two possible primary processes of 1,7-electrocyclisation and 1 ,I -cycloaddition in the reactions of the isoelectronic systems (43) and (47) containing nitrilium and diazonium betaines. R H R' H R' (3) X (13; R = Me) gave the carbene 'dimer' (15; R = Me) (40%) and the azine (16; R = Me) (38%), formed by reaction of the Me H \ + -C=N=N * The conformational assignments of the proximate products (29) and (31) [and also (33) and (%)I are based on a transition state for ring closure of the type shown in (42).

Gold(I) Carbenes by Retro-Buchner Reaction: Generation and Fate

“…A similar transformation had been observed in the thermal decomposition of diazo compounds to form naphtho[ a ]cycloheptenes of type 12 . 31 …”

Reactions of triene-conjugated diazo-compounds: reaction paths from o-(1,3-dienyl)aryldiazomethanes to 3,8-methano-1,2-diazocines and to pyrrolo[2,1-a]phthalazines via intramolecular (3 + 2) and 1,1-cycloaddition reactions

“…All the work in this paper is concerned with the reactions of the γ,δ-cis triene systems 7 (substituents identified in Table 1). They were generated, as in earlier work, 3 by the thermal decomposition of the tosylhydrazone sodium salts 17 under aprotic conditions in 1,2-dimethoxyethane (DME) as solvent (Scheme 3). The aldehydes 16 were prepared by Suzuki coupling reactions of 2-formylphenylboronic acid with the appropriate bromodiene 15.…”

“…Diazo compounds are known to react in some 1,1cycloaddition reactions 2a-c but in general this is a less favoured mode of reaction than it is for nitrile ylides and nitrile imines. Thus, in the reactions of the diene-conjugated systems 10 to give 2,3-benzodiazepines 12, 3 species such as 13 have never been detected although they could in principle be in equilibrium with the quinonoid intermediates 11, and indeed studying the chemistry of 7 would provide a test for the accessibility of 13. At the outset therefore it was impossible to make an accurate prediction of the preferred reaction path for 7 and so an exploratory investigation was undertaken.…”

1,7‐Electrocyclization Reactions of 2‐Aza‐4,5‐benzoheptatrienyl‐ and 4‐Aza‐6,7‐benzononatetraenyllithium Compounds: Synthesis of Novel 2‐Benzazepines and (Benzocyclooctenyl)amines

“…All deprotonations and ring‐closure reactions were carried out with complete exclusion of moisture (argon, modified Schlenk techniques). The aldimines 1a – c , 4a and 4b were synthesized in accordance with literature procedures, from 2‐alkenylbenzaldehydes and benzyl‐ or allylamine:9,19,20 ( E / Z )‐2‐(Alkenyl)bromobenzenes were prepared by Wittig olefination of 2‐bromobenzaldehyde; the 2‐alkenylbenzaldehydes were obtained by formylation of these 2‐(alkenyl)bromobenzenes with n ‐butyllithium and dimethylformamide. EA = ethyl acetate; P = pentane, PE = petroleum ether; TEA = triethylamine.…”