Search Results (11)

(−)-cis-α-Ambrinol is a natural product present in ambergris, a substance of marine origin that has been highly valued by perfumers. In this paper, we present a new approach to its total synthesis. The starting material is commercially available α-ionone and the key step is an intramolecular Barbier-type cyclization induced by CpTiCl₂, an organometallic compound prepared in situ by a CpTiCl₃ reduction with Mn. Full article

A short synthesis of racemic Sacidumlignan B was achieved for the first time. The key steps included a formal reductive coupling between the diaryl ketone and the crotyl bromide, and the subsequent Friedel–Crafts cyclization, which led to an efficient construction of dihydronaphthalene skeleton in this 2,7′-cyclolignan natural product. Full article

The genetic pool of valuable old ornamental cultivars and their in situ maintenance is threated by climate change. Meanwhile, ornamental plants like roses make up an important share of both gardens and urban green spaces, where they are particularly vulnerable to multi-stress growth conditions. The aim of this research was to evaluate the effect of changing climatic conditions on growth and flowering of 11 historic climber roses through long-term studies (2000–2017) conducted in Central Europe. The evaluation of plants consisted of assessment of frost damage and the timing of early phenological stages (starting of bud break, leaf unfolding), as well as gathering data on the beginning, fullness, and end of flowering and its abundance. Frost damage was not observed in any year only in ‘Mme Plantier’ and did not occur for any cultivar after the winter in the years 2007, 2008, and 2014. Only a little damage to one-year shoots was recorded after the winter in the years 2015–2017. Frost damage to ‘Alberic Barbier’, ‘Albertine’, ‘Chaplin’s Pink Climber’, ‘Orange Triumph clg’, and ‘Venusta Pendula’ led to pruning to ground level in every year excluding those listed above. Frost damage of once-blooming roses limited their flowering; however, the many-year datasets showed a trend for decreased frost damage and improved abundance of flowering, and these results can be interpreted as a response to the increase of average air temperature. The timing of bud breaking and leaf development in all climber roses was strictly correlated with average air temperature in the dormancy period. The reactions of climber roses to weather conditions confirmed the influence of climatic changes on ornamental crop plants in Central Europe, introducing the potential possibility for the wider application of climber roses, but without certainty of flowering every year. Full article

The stereo- and regioselective total syntheses of OMe derivatives of the scarce bioactive meroterpenoids makassaric acid (1) and fascioquinol B (2) have been accomplished. The synthetic sequences are based on the following three efficient and selective catalytic reactions: Cu-catalyzed addition of Grignard compounds to an epoxide; a regioselective Barbier-type reaction, catalyzed by Cp₂TiCl; and regio- and stereoselective bioinspired cyclization, also catalyzed by Cp₂TiCl. These three key processes allow us to obtain the main skeletons of 1 and 2 in a few steps. The valuable synthetic proposal shown in this work provides fast access to scarce, structurally complex meroterpenes with promising biological activities, which are a sustainable source for later studies and applications in medicine. Full article

Tetrahydropyran (THP) rings are common in several natural products, therefore, various strategies are being developed to synthesize these rings. The present work described the study of a one-pot synthesis of 2,4,6-trisubstituted tetrahydropyran compounds promoted by the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate [BMIM][PF₆] through a Barbier–Prins reaction between allyl bromide and aldehydes. The use of [BMIM][PF₆] gave Prins products from several aldehydes in good yields and reaction times. We also found that the anion, PF₆-, accelerates the Barbier reaction when used alone, and the excess SnBr₂ from the reaction conditions of the Barbier reaction leads to the formation of the THP rings, thus acting as a catalyst for Prins cyclization. Additionally, we demonstrate that ionic liquid can be recovered and reused five times in the preparation of 4-bromo-tetrahydro-2,6-diphenyl-2H-pyran without significant yield loss. Full article

A Barbier reaction–Heck arylation sequence from α-bromomethylbutenolide to fused tri and tetracyclic lactones has been developed. The first step involving a Barbier reaction enabled installing ortho-bromoaromatics in α-ylidene γ-lactones. The latter substrates were subjected to intramolecular Heck reaction conditions which selectively afforded 6,5,5 or 6,6,5 fused ring systems depending on the nature of the base employed. Full article

In this paper we present the convenient syntheses of six new guanylhydrazone and aminoguanidine tetrahydropyran derivatives 2–7. The guanylhydrazone 2, 3 and 4 were prepared in 100% yield, starting from corresponding aromatic ketones 8a–c and aminoguanidine hydrochloride accessed by microwave irradiation. The aminoguanidine 5, 6 and 7 were prepared by reduction of guanylhydrazone 2–4 with sodium cyanoborohydride (94% yield of 5, and 100% yield of 6 and 7). The aromatic ketones 8a–c were prepared from the Barbier reaction followed by the Prins cyclization reaction (two steps, 63%–65% and 95%–98%). Cytotoxicity studies have demonstrated the effects of compounds 2–7 in various cancer and normal cell lines. That way, we showed that these compounds decreased cell viabilities in a micromolar range, and from all the compounds tested we can state that, at least, compound 3 can be considered a promising molecule for target-directed drug design. Full article

The elemene-type terpenoids, which possess various biological activities, contain a syn- or anti-1,2-dialkenylcyclohexane framework. An efficient synthetic route to the syn- and anti-1,2-dialkenylcyclohexane core and its application in the synthesis of (±)-geijerone and its diastereomer is reported. Construction of the syn- and anti-1,2-dialkenyl moiety was achieved via Ireland-Claisen rearrangement of the (E)-allylic ester, and the cyclohexanone moiety was derived from the iodoaldehyde via intramolecular Barbier reaction. The synthetic strategy allows rapid access to various epimers and analogues of elemene-type products. Full article

The aqueous tin-mediated Barbier reaction affords good to excellent yields and moderate syn diastereoselectivity under basic and acidic conditions. The high yields and stereoselectivity observed in the case of o-substituted aldehydes suggest a cyclic organotin intermediate or transition state in K2HPO4 solution. A practical and efficient aqueous tin allylation of methoxy- and hydroxybenzaldehydes can be carried out in HCl solution in 15 minutes to afford the corresponding homoallylic alcohols in high yields. Aliphatic aldehydes give moderate to excellent yields with reaction times ranging from 30 to 60 minutes. Under these conditions, crotylation gives exclusively the γ-product and the syn isomer is formed preferentially. For 2-methoxybenzaldehyde, an equilibration of the isomers to a syn/anti ratio of 1:1 can be observed after several hours. Control experiments with radical sources or scavengers give no support for radical intermediates. NMR studies suggest a mechanism involving an organotin intermediate. The major organotin species formed depends on the reaction medium and the reaction time. The use of acidic solution reduces the reaction times, due to the acceleration of the formation of the allyltin(IV) species. Full article

The zinc–mediated aqueous Barbier–Grignard reaction of cyclic allylic bromide substrates with various aldehydes and ketones to afford homoallylic alcohols was investigated. Aromatic aldehydes and ketones afforded adducts in good yields (66–90%) and with good diastereoselectivities. Non–aromatic aldehydes also reacted well under these conditions, but only poor yields were obtained with non–aromatic ketones. Regioselectivity was high when some substituted cyclic allylic bromides were investigated. Full article