Pd(0)-Catalyzed Oxy- and Aminoalkynylation of Olefins for the Synthesis of Tetrahydrofurans and Pyrrolidines

The first Pd(0)-catalyzed intramolecular oxy- and aminoalkynylation of nonactivated olefins is reported. The reaction gives access to important tetrahydrofuran and pyrrolidine heterocycles with high diastereoselectivity. The unique synthetic potential of acetylenes is further exploited to access key building blocks for the synthesis of bioactive natural products

Indole- and Pyrrole-BX: Bench-Stable Hypervalent Iodine Reagents for Heterocycle Umpolung

The one-step synthesis of the bench-stable hypervalent iodine reagents IndoleBX and PyrroleBX using mild Lewis acid catalyzed conditions is reported. The new reagents are stable up to 150 degrees C and were applied in the C-H arylation of unactivated arenes using either rhodium or ruthenium catalysts. A broad range of heterocyclic systems of high interest for synthetic and medicinal chemistry was accessed in high yields. The developed C-H functionalization could not be achieved using reported reagents or methods, highlighting the unique reactivity of Indole- and Pyrrole-BX

Intramolecular palladium-catalyzed alkene carboalkynylation

Carbocycles are essential building blocks for the synthesis of natural and synthetic bioactive compounds. Herein, we report the first example of palladium-catalyzed intramolecular carboalkynylation of non-activated olefins. Using activated carbonyl compounds as nucleophiles and an alkynyl bromide as an electrophile, the reaction gives access to cyclopentanes in 44-93% yield and one example of cyclohexane in 31% yield with simultaneous formation of a SP3-SP C-C bond. The reaction therefore combines ring formation with the introduction of a versatile triple bond for further functionalization. (C) 2015 Elsevier Ltd. All rights reserved

A Palladium-Catalyzed Aminoalkynylation Strategy towards Bicyclic Heterocycles: Synthesis of (±)-Trachelanthamidine

Sweet cyclizations: The synthesis of pyrrolizidines and indolizidines has been achieved. Olefins were subjected to an intramolecular palladium-catalyzed aminoalkynylation with the hypervalent iodine reagent TIPS-EBX. After removal of the protecting group, a two-step cyclization sequence and subsequent reduction led to the natural product (±)-trachelanthamidine (see scheme; TIPS-EBX=triisopropylsilyl ethynylbenziodoxolone)

Pd(0)-Catalyzed Alkene Oxy- and Aminoalkynylation with Aliphatic Bromoacetylenes

Tetrahydrofurans and pyrrolidines are among the most important heterocycles found in bioactive compounds. Cyclization-functionalization domino reactions of alcohols or amines onto olefins,constitute one of the most efficient methods to access them. In this context oxy- and aminoalkynylation are especially important reactions because of the numerous transformations possible with the triple bond of acetylenes yet these methods have been limited to the use of silyl protected acetylenes. Herein we report the first palladium-catalyzed oxy- and aminoalkynylation using aliphatic bromoalkynes which proceeded with high diastereoselectivity and functional group tolerance. A one-pot hydrogenation of the triple bond gave then access to alkyl-substituted tetrahydrofurans and pyrroldines. Finally a detailed study of the side products formed during the reaction gave a first insight into the reaction mechanism

Pd-Catalyzed Intramolecular Oxyalkynylation of Alkenes with Hypervalent Iodine

The first example of intramolecular oxyalkynylation of nonactivated alkenes using oxidative Pd chemistry is reported. Both phenol and aromatic or aliphatic acid derivatives could be used under operator-friendly conditions (room temperature, technical solvents, under air). The discovery of the superiority of benziodoxolone-derived hypervalent iodine reagent 3d as an alkyne transfer reagent further expands the rapidly increasing utility of hypervalent iodine reagents in catalysis and is expected to have important implications for other similar processes

Benziodoxole-based hypervalent iodine reagents for atom-transfer reactions

In the last decades, hypervalent iodine reagents have raised from chemical curiosities to mainstream reagents in organic synthesis. The use of benziodoxole-derived reagents has been especially successful in oxidation methods, whereas non-cyclic iodinanes have been used both for oxidation and atom-transfer reactions. On the other hand, the exceptional properties of benziodoxole reagents for atom-transfer reactions have only started to attract the attention of the synthetic community more recently. In this review, progress in the use of these compounds for C–X and C–C bond formations will be presented. In particular, recent breakthroughs in trifluoromethylation and alkynylation reactions have been realized since 2006 based on benziodoxole-derived reagents and these results are the main focus of this article

Evidence that chronic hypoxia causes reversible impairment on male fertility

Aim: To evaluate the effect of chronic hypoxia on human spermatogenic parameters and their recovery time. Methods: Seminological parameters of six male healthy mountain trekkers were evaluated in normoxia at sea level. After 26 days exposure to altitude (ranging from 2 000 m to 5 600 m, Karakorum Expedition) the same parameters were again evaluated after returning to sea level. These parameters were once again evaluated after 1 month and then again after 6 months. Results: Sperm count was found to be lower immediately after returning to sea level (P = 0.0004) and again after a month (P = 0.0008). Normal levels were reached after 6 months. Spermatic motility (%) shows no reduction immediately after returning to sea level (P = 0.0583), whereas after 1 month this reduction was significant (P = 0.0066). After 6 months there was a recovery to pre-hypoxic exposure values. Abnormal or immature spermatozoa (%) increased immediately after returning to sea level (P = 0.0067) and then again after 1 month (P = 0.0004). After 6 months there was a complete recovery to initial values. The total number of motile sperm in the ejaculate was found to be lower immediately after returning to sea level (P = 0.0024) and then again after 1 month (P = 0.0021). After 6 months there was a recovery to pre-hypoxic exposure values. Conclusion: Chronic hypoxia induces a state of oligospermia and the normalization of such seminological parameters at the restoration of previous normoxic conditions after 6 months indicate the influence of oxygen supply in physiological mechanisms of spermatogenesis and male fertility. (Asian J Androl 2008 Jul; 10: 602–606

Benziodoxole-based hypervalent iodine reagents for atom-transfer reactions

In the last decades, hypervalent iodine reagents have raised from chemical curiosities to mainstream reagents in organic synthesis. The use of benziodoxole-derived reagents has been especially successful in oxidation methods, whereas non-cyclic iodinanes have been used both for oxidation and atom-transfer reactions. On the other hand, the exceptional properties of benziodoxole reagents for atom-transfer reactions have only started to attract the attention of the synthetic community more recently. In this review, progress in the use of these compounds for C-X and C-C bond formations will be presented. In particular, recent breakthroughs in trifluoromethylation and alkynylation reactions have been realized since 2006 based on benziodoxole-derived reagents and these results are the main focus of this article