New routes to 1,1-dichloro-4-methyl-1,3-pentadiene (original) (raw)
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Synthesis of Meso-Substituted Chlorins via Tetrahydrobilene- a Intermediates
The Journal of Organic Chemistry, 2001
Chlorin building blocks incorporating a geminal dimethyl group in the reduced ring and synthetic handles in specific patterns at the perimeter of the macrocycle are expected to have utility in biomimetic and materials chemistry. A prior route employed condensation of a dihydrodipyrrin (Western half) and a bromodipyrromethane-monocarbinol (Eastern half), followed by oxidative cyclization of the putative dihydrobilene-a to form the meso-substituted zinc chlorin in yields of ∼10%. The limited stability of the dihydrodipyrrin precluded study of the chlorin-forming process. We now have refined this methodology. A tetrahydrodipyrrin Western half (2,3,4,5-tetrahydro-1,3,3-trimethyldipyrrin) has been synthesized and found to be quite stable. The condensation of the Western half and an Eastern half (100 mM each) proceeded smoothly in CH 3 CN containing 100 mM TFA at room temperature for 30 min. The resulting linear tetrapyrrole, a 2,3,4,5tetrahydrobilene-a, also is quite stable, enabling study of the conversion to chlorin. Refined conditions for the oxidative cyclization were found to include the following: the tetrahydrobilene-a (10 mM), AgTf (3-5 molar equiv), Zn(OAc) 2 (15 molar equiv), and 2,2,6,6-tetramethylpiperidine (15 molar equiv) in CH 3 CN at reflux exposed to air for 4-6 h, affording the zinc chlorin. The chlorinforming process could be implemented in either a two-flask process or a one-flask process. The two-flask process was applied to form six zinc chlorins bearing substituents such as pentafluorophenyl, 3,5-di-tert-butylphenyl, TMS-ethyl benzoate, iodophenyl, or ethynylphenyl (deprotection of the TMS-ethynyl group occurred during the oxidative cyclization process). The stepwise yields (isolated) for the condensation and oxidative cyclization processes forming the tetrahydrobilene and zinc chlorin were 32-72% and 27-62%, respectively, giving overall yields of zinc chlorin from the Eastern and Western halves of 12-45%. Taken together, the refinements introduced enable 100-mg quantities of chlorin building blocks to be prepared in a facile and rational manner.
J Org Chem, 1981
Reaction of Silver Acetate and Iodine with lg. Starting materials were 0.735 g of silver acetate and 0.396 g of lg; purification of the crude reaction product by preparative layer chromatography (CHC13) afforded 0.360 g (72%) of pure 2iodocyclooctanone, 6c: molecular distillation 45 "C (2 mm) [lit? 45 OC (1.75 mm)]; nzsD 1.5490 (lita5 n23D 1.5494); IR (neat) 1700 cm-'. Reaction of Silver Benzoate and Iodine with lg. Starting materials were 1.010 g of silver benzoate and 0.396 g of lg; purification of the crude reaction product by preparative layer chromatography (CHC13) afforded 0.356 g (71%) of pure 6c: molecular distillation 45 "C (2 mm) [lita5 45 OC (1.75 mm)]; IR (neat) 1700 cm-'. Reaction of Silver Acetate and Iodine with lh. Starting with 0.735 g of silver acetate and 0.508 g of l h afforded a 1:4 mixture (NMR) of 3q and 6d. Preparative layer chromatography (CHCld of the mixture afforded pure 2-acetoxycyclododecanone, 3q, and 2-iodocyclododecanone, 6d. 2-Acetoxycyclododecanone, 3q: 0.072 g (15%); mp 83-84
Synthetic studies towards pentacyclic triterpenes
Arboranes and fernanes are pentacyclic triterpenes. Isoarborinol, suggested to be a cholesterol surrogate in the membranes of some undefined bacteria (Guy Ourisson), a hybride of migrated hopanes and parkeol, contains five cycles, 9 asymmetric centers (512 possible stereoisomers) hence a feasible total synthesis requires a plan involving a very high degree of stereoselectivity. In contrast to the massive amount of research, which has been directed toward the total synthesis of taxanes and mevinic acids, little attention has been paid to arborane and fernane type pentacyclic triterpenes. The challenge was: could we achieve the synthesis of natural and unnatural analogues of arborane and fernane derivatives using the same ingredients in a common synthetic scheme whith enzyme like selectivities? Plants produce one or more cyclases that convert squalene or its epoxide into a complete series of triterpenoid products in which the molecules posses both an epimeric and antipodal steric arrangement of the ring systems. According to the literature, differences in various biological properties of these migrated hopanes could be related to the stereochemistry of the ring system and of the isopropyl group attached to C-21. Plant extraction from several tropical plants will give the exact molecule but not the nor-14 or nor-21 analogues as there is no way for removing the angular methyl group at C-14 or isopropyl group at C-21, to synthesize molecules for biological tests. We first favored an AB+DE-→ ABCDE approach, anticipating that joining the diene AB 2 and dienophile DE ring 3 precursors should correctly situate the chiral centers at C10 and C17, furthermore ensuring the right orientation. The ester group in 3 should initially serve to activate the dienophile during the [4+2] before its transformation to the C13 angular methyl group. This plan was thwarted by the wrong orientation of the reactants. The carbonyl preferred an exo orientation and led to the unnatural skeleton 7/8, the ester group having served both as a good activating group and as an exclusive control element.
Synthesis and Rearrangement of 3-Methyl-1,4-pentadiyne-3-ol
Molecules, 2002
An efficient synthesis and rearrangement of 3-methyl-1,4-pentadiyne-3-ol (1) using perrhenate-and Mo(VI)-catalysts is reported. The by-products 3,6-dimethyl-1,4,7octatriyne-3,6-diol (2) and 3-ethynyl-5-methyl-1,6-heptadiyne-3,5-diol (3) were isolated and spectroscopically characterized. A possible reaction mechanism for the formation of the byproducts is discussed.
Recent Advances in the Chemistry of Pentafulvenes
Chemical Reviews, 2017
Pentafulvenes are a unique class of compounds that originally attracted attention due to their propensity to display nonbenzenoid aromaticity. Subsequently, they were recognized as valuable synthons for the construction of a wide range of compounds by virtue of their ability to display multiple cycloaddition profiles. Naturally, this area of organic chemistry has experienced rapid growth over the last five decades, fueled by elegant work showcasing the unique reactivity of pentafulvenes in a plethora of cycloaddition reactions. In this Review, we have attempted to provide a systematic account of the methods for the generation of pentafulvenes, their rich and varied cycloaddition chemistry, organometallic reactions, and theoretical studies that support their versatility. Further, we have highlighted their applications in the synthesis of a variety of complex structural frameworks. It is our conviction that this Review will be useful to a wide range of chemists, and will spur further research in this promising area.
Journal of the American Chemical Society, 1996
The reactions of [Pd(C 6 F 5 )Br(CH 3 CN) 2 ] with 1,4-pentadiene or 3-methyl-1,4-pentadiene at low temperature afford, after insertion of one double bond into the Pd-C 6 F 5 bond, two types of η 1 -η 2 -pentenylpalladium derivatives: the 4.5-membered palladacycles [Pd 2 (µ-Br) 2 (5-Pf-3-R-1,2,4-η 1 -η 2 -pentenyl) 2 ] (Pf ) C 6 F 5 ; R ) H (2a), Me (2b)) and the 5.5-membered metallacycles [Pd 2 (µ-Br) 2 (5-Pf-3-R-1,2,5-η 1 -η 2 -pentenyl) 2 ] (R ) H (3a), Me (3b)). Both enyls isomerize to η 3 -allylic derivatives following two competitiVe pathways, i.e. (i) Pd migration or (ii) cyclopropane formation and reopening, which lead to the isomeric η 3 -allylpalladium complexes [Pd 2 (µ-Br) 2 (5-Pf-3-R-1-3-η 3pentenyl) 2 ] (R ) H (5a), Me (5b)) and [Pd 2 (µ-Br) 2 (4-Pf-3-(CH 2 R)-1-3-η 3 -butenyl) 2 ] (R ) H (6a), Me (6b)), respectively. After the cyclopropane formation-reopening process, [Pd 2 (µ-Br) 2 (3-CH 2 Pf-1,2,5-η 1 -η 2 -pentenyl) 2 ] (8) is also formed which isomerizes to 6b. The reaction of a mixture of the η 1 -η 2 -pentenyl complexes at low temperature with CO/NaOMe gives methyl ester derivatives. Again, the formation of the major ester CH 2 dCH(CH 2 Pf)-CHRCOOMe involves cyclopropane formation-reopening in the enyl derivative 2. An unusual acyl complex, [Pd-(µ-Br)(η 1 -η 2 -3-CH 2 Pf-1-oxo-4-pentenyl)] 2 (15) containing a chelating η 2 -η 1 -olefin acyl moiety has been characterized. + + Scheme 2 Scheme 3 7146
Gallium(III) Halide Promoted Synthesis of 1,3,5-Triaryl-1,5-dihalo-1,4-pentadienes
ChemInform, 2005
Aryl substituted alkynes undergo smooth coupling with aldehydes in the presence of gallium (III) halides under extremely mild conditions to afford the corresponding 1, 3, 5-triaryl-1, 5-dihalo-1, 4-pentadienes in good yields with E, Z-selectivity. Similarly 1, 3, 5-triaryl-1, 5-...
A convenient route to prepare isodicyclopentadiene—precursor of 1,5-dihydro-pentalene
Tetrahedron Letters, 2007
A new route to prepare tricyclo[5.2.1.0 2,6 ]deca-2,4-diene (isodicyclopentadiene) was developed. This new route passes through a brominated (5-bromotricyclo[5.2.1.0 2,6 ]dec-3-ene) derivative obtained from tricycle[5.2.1.0 2,6 ]dec-3-ene (8,9-dihydrodicyclopentadiene) and NBS with a good yield. The complete assignment of protons and carbons on nuclear magnetic resonance spectra was done for dicyclopentadiene and the chemically transformed compounds by 2D NMR techniques.