4-π-Photocyclization of 1,2-Dihydropyridazines: An Approach to Bicyclic 1,2-Diazetidines with Rich Synthetic Potential.

The 4-π-photocyclization of a range of 1,2-dihydropyridazines is described, generating bicyclic 1,2-diazetidines in high yields on multigram scale. The key bicyclic 1,2-diazetidines are versatile synthetic intermediates and were easily converted into a range of novel derivatives, including functionalized 1,2-diazetidines, cyclobutenes, cyclobutanes, and 1,3-dienes

An efficient preparation of 1,2-dihydropyridazines through a Diels-Alder/palladium-catalysed elimination sequence

© 2019 Elsevier Ltd A convenient, scalable synthesis of 1,2-dihydropyridazines is presented, based on the Diels-Alder cycloaddition of 1-acetoxy-1,3-butadiene with a variety of azo compounds, followed by a palladium-catalysed elimination. The products are produced on multigram scale and the new method is particularly efficient and atom-economical when compared with previous preparations of 1,2-dihydropyridazines

Synthesis and organolithium-mediated reactions of β-methoxy aziridines : scope and synthetic applications

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Unexpected products from the attempted organolithium-mediated conversion of beta-methoxy aziridines into allylic amines

The organolithium-mediated conversion of cyclic trans-p-methoxy aziridines and cis-beta-methoxy aziridines with a tertiary alkoxy group adjacent to the aziridine into the corresponding substituted allylic sulfonamides is reported. In all cases, unexpected products were observed and the reactivity was completely different from other related cis-beta-methoxy aziridines. The product distributions are highly dependent on the organolithium reagent employed and the structure of the methoxy aziridine Thus, together with our previous reports, the full scope and limitations of this approach to allylic sulfonamides are established

Stereoselective aziridination of cyclic allylic alcohols using chloramine-T

The stereoselective aziridination of a range of cyclic allylic alcohols using two different chloramine salts (4-MeC(6)H(4)SO(2)NClNa, TsNClNa and t-BuSO(2)NClNa, BusNClNa) has been explored. The stereoselectivity of these reactions was highly dependent on the structure of the allylic alcohol and the chloramine salt. Generally, mixtures of cis- and trans-hydroxy aziridines were obtained, in which the major diastereomer was the cis- hydroxy aziridine, whilst complete cis-diastereoselectivity was observed in the aziridination of 1,3-disubstituted allylic alcohols. In each case studied, aziridination using BusNClNa gave higher cis- stereoselectivity than that observed for the same reaction using TsNClNa. Unexpectedly, application of the aziridination conditions to 1-substituted cyclopen-2-en-1-ols did not generate the aziridines. Instead, epoxy sulfonamides were obtained

Exploiting Sm(II) and Sm(III) in SmI2-initiated reaction cascades:application in a tag removal-cyclisation approach to spirooxindole scaffolds

A tag removal-cyclisation sequence is described that is initiated by reduction using a Sm(II) species and completed by a Sm(III) Lewis acid that is formed in an earlier stage. Therefore, the reaction cascade utilises both oxidation states of a samarium reagent in discrete steps and allows access to privileged, pyrrolidinyl-spirooxindole scaffolds and analogues inspired by the anti-cancer natural product spirotryprostatin A

Synthesis of functionalized spirocyclic oxetanes through Paternò–Büchi reactions of cyclic ketones and maleic acid derivatives †

A telescoped three-step sequence to functionalised spirocyclic oxetanes is reported, involving Paternò–Büchi reactions between maleic acid derivatives and cyclic ketones. p-Xylene suppresses the competing alkene dimerization that has plagued previous work, allowing access to 35 novel spirocyclic oxetanes that cannot be prepared using existing methodologies, and which represent versatile intermediates for further elaboration

Preparation and Synthetic Applications of Phototropone

An optimized multigram-scale route to phototropone (bicyclo[3.2.0]hepta-2,6-dien-7-one) is reported via the 4-π-photocyclization of tropone complexed to Lewis acid. Phototropone is a highly versatile molecular building block, and its conversion into 18 novel derivatives using standard transformations is demonstrated, allowing access to a variety of rigid bicyclic scaffolds

alpha-Acyloxynitroso dienophiles in [4+2] hetero Diels-Alder cycloadditions:mechanistic insights

alpha-Acyloxynitroso derivatives are a class of heterodienophiles leading to valuable 3,6-dihydro-1,2-oxazines or the corresponding aminoalcohols in good yields. The discovery that a beta-oxygenated moiety led to a domino [4+2] cycloaddition/sigma(N-O) bond cleavage in the presence of a catalytic amount of Lewis acid was investigated in detail, through kinetic profiling of the reaction both in the absence and presence of a promoter. These studies showed that the role of the Lewis acid was to accelerate the sigma(N-O) bond cleavage thereby promoting a highly reproducible sequence. In addition, our preliminary results on an asymmetric version of this domino sequence are reported. (C) 2010 Elsevier Ltd. All rights reserved