Cycloheptene moieties

The interesting tricyclic compound 55 49), which has ( )-cycloheptene moiety, was found to be very labile and could only be trapped by condensing with diphenyl-isobenzofuran. 

The results are based on variable-temperature (VT) H NMR studies of 23-31. The results are close to those found for 2-aminoacetophenone, AG = 10.5 0.5 kcalmol-180. In addition, for the four compounds 25-28 characterized by the cycloheptene moiety, a slow ring interconversion from chair to chair was evident. For compounds 25, 27 and 28 the experimental AG values were 9.4, 10.2 and 10.0 kcalmol-1, and the corresponding coalescence temperatures were 204, 220 and 215 K, respectively. For compound 26 these values are not available. 

For the desymmetrization, 448 was transformed into the monoenoltriflate, which in a palladium-catalyzed couphng reaction provided tetraolefin 450, ready for a Grubbs-Hoveyda cydization generating the cycloheptene moiety of449. 

In another conceptually novel [5 + 2]-process, Tanino and co-workers synthesized cycloheptene derivatives by stereoselective [5 + 2]-cycloadditions involving hexacarbonyldicobalt-acetylene complexes as the five-carbon component and enol ethers as the two-carbon component (Schemes 22 and 23).60 61 The role of the dicobalthexacarbonyl complex is to facilitate formation and reaction of the propargyl cation putatively involved as an intermediate in this reaction. The dicobalthexacarbonyl moiety can be removed using various conditions (Scheme 24) to provide alkane 60, alkene 62, and anhydride 63. 

This finding is rooted in the DMSO promoter and Krafft s demonstration that a suitably positioned sulfur moiety tethered to the PK precursor increases the reaction efficiency. The reaction conditions with these promoters generally require much higher reaction temperatures than that with oxidative promoters, and complete the reaction in substantially shorter periods to give high chemical yields. Moreover, the sulfur additive promotes the intermolecular PKR with even unstrained and less reactive olefins. A prominent example is the reaction between phenylacetylene and cycloheptene (Equation (3)). ... 

Samarium iodide has been used to reduce sulfonylated oxabicydic substrates leading to the elimination of the ft oxygen moiety. Molander used this strategy for the synthesis of substituted cycloheptenes and cyclooctenes, Eq. 155 [81]. 

The Rh(trop2dach) complex (trop2dach = 1,4-bis(5//-dibenzo a,<7 -cyclohepten-5-yl)-l, 2-diamino-cyclohexane) was synthesized and its structure was computed29 and the spin density was found to be highly delocalized over the two trop moieties. The spin population was about 36% at the rhodium atom. The structure of the complex and the continuous-wave EPR spectrum of its frozen solution at X-band is depicted in... 

The reaction mechanism leading to advanced intermediate 85 starts with rhodium insertion into the aldehyde moiety. Rhodacycle formation follows to promote hydroacylation into the 4,6-diene providing cycloheptene compound 86. Then, rhodium catalyze a highly regioselective cycloisomerization reaction on the resulting triene to produce the final product 87 (Scheme 7.54 please refer also to Scheme 7.51). 

Asymmetric desymmetrization of m sr>-cycloheptene-l,4-diol bis-silyl etho-d by using the Rh(I)-(5)-BINAP catalyst gave (S)-4-hydroxycycloheptanone (5) with 71 % ee (Scheme 3A.2). Asymmetric isomerization of 4-tert-butyl-1 -vinylcyclohexane (6) catalyzed by bis(indenyl)-titanium complex (8) bearing a chiral bridging moiety afforded (S)-4-te/t-butyl-l-ediylidenecy-clohexane (7) with up to 80% ee (Scheme 3A.3). " ... 

Likewise, the cycloisomerization of the sulfonamide tethered substrates resulted in an efficient synthesis of the spiro-alkaloids A2 and/or B2 of various ring sizes, with excellent enantioselectivities and high yields [23]. In this case also, product selectivity depends on the ring size of the cyclic olefin moiety the 15 membered cyclic substrate (n = 11) and the cyclopentene derivative (n — 1) afford isomers A2 selectively, while B2 is the major product obtained from a cycloheptene derivative n = 3). 

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