Theoretical studies on the intramolecular cyclization of 2,4,6-t-Bu₃C₆H₂P=C: and effects of conjugation between the P=C and aromatic moieties

• Masaaki Yoshifuji and
• Shigekazu Ito

Beilstein J. Org. Chem. 2014, 10, 1032–1036, doi:10.3762/bjoc.10.103

• 2 to 1 were determined as 95.0 kcal/mol and 91.5 kcal/mol, respectively. Whereas the P1–C1 distance is typical for phosphaalkenes [21], dihedral angle of the P=C and almost planar benzene ring is close to co-planar due to the fused 6-membered ring [τ(C1–P1–C3–C4] = 22.9°, τ(C1–P1–C3–C9) = 160.1

Site-selective covalent functionalization at interior carbon atoms and on the rim of circumtrindene, a C₃₆H₁₂ open geodesic polyarene

• Hee Yeon Cho,
• Ronald B. M. Ansems and
• Lawrence T. Scott

Beilstein J. Org. Chem. 2014, 10, 956–968, doi:10.3762/bjoc.10.94

• surpasses that in fullerene C60 (POAV angle = 11.6°, Figure 4). Moreover, the X-ray structure of circumtrindene (6) reveals that the carbon–carbon bonds around the 6-membered ring at the top of the dome are not equivalent. The bond lengths vary depending on their location (Figure 5), as is also observed in

• fullerenes [53]. The carbon–carbon bond shared by two six-membered rings (so-called 6:6-bonds: 1.379 Å) are shorter than those shared by a 5-membered ring and a 6-membered ring (5:6-bonds: 1.430 Å). That is, the carbon–carbon bonds of the hexagonal ring in the center of circumtrindene are not the same as

Isocyanide-based multicomponent reactions towards cyclic constrained peptidomimetics

• Gijs Koopmanschap,
• Eelco Ruijter and
• Romano V.A. Orru

Beilstein J. Org. Chem. 2014, 10, 544–598, doi:10.3762/bjoc.10.50

Cyclic phosphonium ionic liquids

• Sharon I. Lall-Ramnarine,
• Joshua A. Mukhlall,
• James F. Wishart,
• Robert R. Engel,
• Alicia R. Romeo,
• Masao Gohdo,
• Sharon Ramati,
• Marc Berman and
• Sophia N. Suarez

Beilstein J. Org. Chem. 2014, 10, 271–275, doi:10.3762/bjoc.10.22

• most significant effects observed for the replacement of a methyl group with a phenyl ring in this family of cations are the substantial increases of 19 °C and 30 °C in the glass-transition temperatures for the 5- and 6-membered ring cations respectively. Similar effects on Tg have been reported for

Some aspects of radical chemistry in the assembly of complex molecular architectures

• Béatrice Quiclet-Sire and
• Samir Z. Zard

Beilstein J. Org. Chem. 2013, 9, 557–576, doi:10.3762/bjoc.9.61

• former involves the addition of a butanoyl radical derived from the corresponding S-butanoyl xanthate, while the latter results from the addition of β-xanthyl ketone 84. The use of an α-xanthyl ketone gives rise ultimately to a fused 6-membered ring, as shown by the formation of tricyclic product 88 from

Palladium-catalyzed dual C–H or N–H functionalization of unfunctionalized indole derivatives with alkenes and arenes

• Gianluigi Broggini,
• Egle M. Beccalli,
• Andrea Fasana and
• Silvia Gazzola

Beilstein J. Org. Chem. 2012, 8, 1730–1746, doi:10.3762/bjoc.8.198

• 6-membered ring, once again producing vinyl-substituted products. An analogous process for the direct intramolecular C–H functionalization of inactive alkenyl aryl ethers, giving benzofuran and dihydrobenzofuran derivatives, was successfully developed [67]. Both possible mechanistic pathways based

Two-directional synthesis as a tool for diversity-oriented synthesis: Synthesis of alkaloid scaffolds

• Kieron M. G. O’Connell,
• Monica Díaz-Gavilán,
• Warren R. J. D. Galloway and
• David R. Spring

Beilstein J. Org. Chem. 2012, 8, 850–860, doi:10.3762/bjoc.8.95

• in which ring has the side chain cis to the ring junction hydrogen. The favoured product was the 4,11-trans-7,11-cis isomer (trans-7) in which the side chain of the 6-membered ring is cis to the ring junction proton; this compound was isolated in 55% yield. The alternative 4,11-trans-4,7-cis isomer

An intramolecular inverse electron demand Diels–Alder approach to annulated α-carbolines

• Zhiyuan Ma,
• Feng Ni,
• Grace H. C. Woo,
• Sie-Mun Lo,
• Philip M. Roveto,
• Scott E. Schaus and
• John K. Snyder

Beilstein J. Org. Chem. 2012, 8, 829–840, doi:10.3762/bjoc.8.93

• -lactone was produced in good yield (80%). In contrast, 17b, with the longer tether (n = 2) failed to produce the desired δ-lactone under any conditions. A sharp decrease in reactivity in intramolecular IEDDA reactions of alkynes tethered to 1,2,4-triazines upon progression from 5- to 6-membered ring

• annulations was previously noted by Taylor [95][96][97][98], and has been ascribed to the greater entropy loss for the larger rings [99]. Indeed, it has been estimated that the effective molarity for 5-membered ring closures can be as high as 1,000-fold greater in comparison to 6-membered ring cyclizations

Recent advances in the gold-catalyzed additions to C–C multiple bonds

• He Huang,
• Yu Zhou and
• Hong Liu

Beilstein J. Org. Chem. 2011, 7, 897–936, doi:10.3762/bjoc.7.103

• enantiomer) in excellent yields (Scheme 6). A range of variously substituted triols was prepared which were cyclized to give substituted 5- and 6-membered ring spiroketals. Similarly, the synthesis of the bisbenz-annelated spiroketal core 35 of natural bioactive rubromycins via a gold-catalyzed double

Synthetic applications of gold-catalyzed ring expansions

• David Garayalde and
• Cristina Nevado

Beilstein J. Org. Chem. 2011, 7, 767–780, doi:10.3762/bjoc.7.87

• synthesis of both molecules. In addition, 3- and 1-substituted cyclopropyl propargylic acetates 98 and 99 have also been intensively studied and provide access to 5- and 6-membered ring enones, respectively (Scheme 29) [62][63][64]. In the former substrates, experimental as well as computational evidence

Anion–π interactions influence pK_a values

• Christopher J. Cadman and
• Anna K. Croft

Beilstein J. Org. Chem. 2011, 7, 320–328, doi:10.3762/bjoc.7.42

• and is accompanied by a ring critical point from the 6-membered ring made from the additional atoms of the naphthalene moiety. The ρ value is, as can be surmised from the lower interaction energy, lower for the bond critical point between H and C for 2(a) (0.0193 e·bohr−3) than for that between H and

Reciprocal polyhedra and the Euler relationship: cage hydrocarbons, C_nH_n and closo-boranes [B_xH_x]²⁻

• Michael J. McGlinchey and
• Henning Hopf

Beilstein J. Org. Chem. 2011, 7, 222–233, doi:10.3762/bjoc.7.30

• taking advantage of methodology established during the dodecahedrane project. Undecahedrane, C18H18, 15 The reciprocal polyhedron to the octadecahedron B11H112−, 7, is the C2v [42.58.6]undecahedrane, 15 (Figure 7). Note that this C18H18 system contains a 6-membered ring paralleling the C2v symmetry of

The allylic chalcogen effect in olefin metathesis

• Yuya A. Lin and
• Benjamin G. Davis

Beilstein J. Org. Chem. 2010, 6, 1219–1228, doi:10.3762/bjoc.6.140

• protecting groups, such as a methyl group, were used. Furthermore, when no protecting group was used (i.e., R = R′ = H, Scheme 2) the RCM reaction was unselective and resulted in a 1:1 mixture of 5- and 6-membered ring products. The selectivity for dihydropyran formation was therefore tuned by substitution

Carbasugar analogues of galactofuranosides: α-O-linked derivatives

• Jens Frigell and
• Ian Cumpstey

Beilstein J. Org. Chem. 2010, 6, 1127–1131, doi:10.3762/bjoc.6.129

• -membered ring series, irrespective of the preferred envelope conformation of the epoxide, and that stereoelectronic effects are thus likely to be much less relevant for the more flexible cyclopentane derivatives. One factor that could speak against good regioselectivity in this case would be the fact that

• the β-talo 1,2-epoxide 4. In 5-membered rings, nucleophilic attack at either carbon of an epoxide (with an envelope conformation) would result in a product with a twist-boat conformation, meaning that there was no great difference in energy between the two regioisomers as was the case in the 6

Redox-active tetrathiafulvalene and dithiolene compounds derived from allylic 1,4-diol rearrangement products of disubstituted 1,3-dithiole derivatives

• Filipe Vilela,
• Peter J. Skabara,
• Christopher R. Mason,
• Thomas D. J. Westgate,
• Asun Luquin,
• Simon J. Coles and
• Michael B. Hursthouse

Beilstein J. Org. Chem. 2010, 6, 1002–1014, doi:10.3762/bjoc.6.113

• this process is the competing electrophilic attack of the allylic carbocation at the 3-position of the thiophene ring bearing the carbinol group, forming a new C–C bond and producing a 6-membered ring. Concomitantly, the cationic centre migrates to produce a C=S+ form, where it is stabilised by π

• -electron density. The second hydroxy group is eliminated in a dehydration process. Loss of a further proton affords the neutral product 3 with a fully aromatised 6-membered ring. This process bears similarities to other rearrangements that are well known in classical organic chemistry [7][8][9]. The

Synthesis of chiral cyclohexanes and carbasugars by 6-exo-dig radical cyclisation reactions

• Rajeev K. Shrivastava,
• Elise Maudru,
• Gurdial Singh,
• Richard H. Wightman and
• Keith M. Morgan

Beilstein J. Org. Chem. 2008, 4, No. 43, doi:10.3762/bjoc.4.43

• corresponding aldehydes which on treatment with Grignard reagents afforded a mixture of alcohols. The corresponding iodides underwent similar 6-exo-dig cyclisation to give fully functionalised cyclohexanes. Keywords: carbasugars; cyclisation; cyclohexanes; 6-membered ring; stereoisomers; Introduction The use

Diels- Alder reactions using 4,7-dioxygenated indanones as dienophiles for regioselective construction of oxygenated 2,3-dihydrobenz[f]indenone skeleton

• Natsuno Etomi,
• Takuya Kumamoto,
• Waka Nakanishi and
• Tsutomu Ishikawa

Beilstein J. Org. Chem. 2008, 4, No. 15, doi:10.3762/bjoc.4.15

• compounds had been originally characterized as cyanamides 1 with a linearly-fused 6-6-5-6 membered ring system [11][12]; however, the structure was revised to diazoalkanes 2 by spectroscopic means [13][14] and by total synthesis [15][16][17] (Figure 1). In our total synthesis of methyl-kinamycin C (3) [21

Synthesis of dihydrophenanthridines by a sequence of Ugi-4CR and palladium- catalyzed intramolecular C-H functionalization

• Florence Bonnaterre,
• Michèle Bois-Choussy and
• Jieping Zhu

Beilstein J. Org. Chem. 2008, 4, No. 10, doi:10.3762/bjoc.4.10

• preferentially (entry 11). The cyclization of 6l could in principle provide a 6-membered as well as a 7-membered ring [37], however, only the cyclization leading to the 6-membered ring occurred to provide 1l in 80% yield. Finally, cyclization of 6i gave only one regioisomer 1i resulting from the activation of C4

The tert- amino effect in heterocyclic chemistry: Synthesis of new fused pyrazolinoquinolizine and 1,4-oxazinopyrazoline derivatives

• Dipak Prajapati and
• Kalyan Jyoti Borah

Beilstein J. Org. Chem. 2007, 3, No. 43, doi:10.1186/1860-5397-3-43

• undergoing a 1,5-(4 → 5) hydride shift prior to cyclization to yield a 6-membered ring product 6 (Scheme 2). This is in contrast to an earlier report by Sandhu et al to obtain pyrrolo [2,3-d]pyrimidines from 6-tert-amino-substituted uracils and dimethyl acetylenedicarboxylate.[32] However, further work is in