Tricyclo[2.1.0.0^2,5]pentan‐3‐one

Abstract

Reaction of the 2-configurated trimethylsilyl enol ether of propiophenone with 1/TiCI4 leads to formation of practically only one (9) of the four possible diastereomers; this product, formed via chelation control, has syn-stereochemistry at the two new chiral centers. Since the Mukaiyama aldol addition normally affords mixtures of syn/ anti-adducts"], an unusual phenomenon is operating. SnCl, gives the same result. 9 9 7 : 3 10 23 24 990 25 > 9 9 : < l 26of TiCI, suggest formation of the chelate 24 before stereoselective introduction of the allyl moiety.

Excited State Aromaticity and Antiaromaticity: Opportunities for Photophysical and Photochemical Rationalizations

“…It is Scheme 18. Photochemical Formation of Cyclobutadiene Using Various Precursors Such as Compounds 106, 127,320−323 108, 326 109, 318 110, 327 111, 319,324,325 112, 328 113, 326,327 114, 332 115, 331 116, 330 117, 334 and 118 329 particularly noteworthy that one of the new π-bonds formed is part of the CBD ring. Precursor 114, on the other hand, is interesting as the Fe(CO) 3 fragment formed upon decomposition is not a stable molecule, and both the CBD and Fe(CO) 3 products were only detected as short-lived intermediates by kinetic mass spectrometry.…”

Bicyclo[1.1.1]pentanes, [n]Staffanes, [1.1.1]Propellanes, and Tricyclo[2.1.0.02,5]pentanes

“…Potassium fluoride in acetonitrile cleaved trimethylsilyl groups off the ketone 99i to yield the parent tricyclo[2.1.0.0 2,5 ]pentan-3-one ( 98 , Scheme ) 46 …”

“…41 Potassium fluoride in acetonitrile cleaved trimethylsilyl groups off the ketone 99i to yield the parent tricyclo[2.1.0.0 2,5 ]pentan-3-one (98, Scheme 46). 203 The tricyclo[2.1.0.0 2,5 ]pentane derivative 100a is reduced with sodium naphthalene to a mixture of bicyclo[1.1.1]pentanes 199 in moderate yield (Scheme 47). 36 Similarly, the central bond in 2,4-trimethylene-[1.1.1]propellane (9a) is reduced with lithium metal in diethylamine to the corresponding bicyclo[1.1.1]pentane 200 in 63% yield (Scheme 48).…”

Density Functional Theory Study of Ultrashort and Overlong CC Single Bonds and the Lowest Nonbonding C···C Distance

“…2 For this bridging bond, the picture that emerges from the MO localization is in full agreement with the electron density distribution determined from the X-ray data: 2 the CC bond has no π character and can be described as a classical two-center σ bent bond, formed by hybrid orbitals sp 3.63 pointing about 39°o utward from the line joining the two carbon atoms (by reference, at the same level of theory, in ethane these hybrids are sp 2.28 ). As a matter of fact, the parent compound tricyclo-[2.1.0.0 2,5 ]pentan-3-one has also been synthesized and fully characterized, 20 but no experimental structure has yet been reported. For this molecule, at the same level of theory, the DFT calculations predict a central bond of 1.426 Å and a folding angle δ of 96.2°, rather similar to the structural parameters of its dimethyl derivative TCPO.…”

“…In particular, with reference to the carbons involved in the "special" CC single bonds the following comments can be made. In the case of the bent bond in TCPO, the high shielding 25 and downfield displacement of about 16 ppm relative to its unsubstituted parent (-1.0 ppm), 20 as a consequence of replacement of H atoms by methyl groups, are correctly accounted for. On the other hand, in the case of the unbent bond, the resonance is predicted to move from upfield in bitetrahedrane (-23.5 ppm) toward downfield in BTHEX (32 ppm) and BTHEP (40 ppm), the observed change of 9 ppm of the signal on passing from BTHEX to BTHEP 26 being accurately reproduced by the CSGT calculations.…”