Addition, regioselectivity

The structure of this compoimd 63a was determined by H and C NMR spectroscopy. The H NMR spectrum shows singlets at 1.45 ppm for the methyl protons, and at 4.17 and 6.30 ppm for the hydroxylic and ethylenic protons. The addition regioselectivity in the formation of 63a was established by H- C HMBC 2D-NMR, which shows the C5-C4-C3-Me linkages. The ethylenic proton correlates only with three carbon atoms Ce, C5, and C3. The methyl protons correlate with C3 and with the ethylenic carbon C4, consistent with the neighboring C3-C4 connection. The NOESY spectrum shows... 

A net C—O to C—C bond chirality transfer has been demonstrated in the preparation of a cyclopropane (equation 344).428 Another C—O to C—C chirality transfer was accomplished starting with an optically active alkylidenetetrahydrofuran 429 Not only was complete stereospecificity via a double inversion mechanism observed, but, in addition, regioselectivity had to be exercised to avoid the alternate cycliza-tion to give a seven-membered ring product (equation 345). 

Multi-dimensional NMR was also the tool in the structure elucidation of dihydroazocine 10 in order to prove the addition regioselectivity <2003JOC1447>, and in the synthesis of various benzazocines via Beckmann rearrangement <2006TL4721>. 

In addition, regioselective enzymatic acylation of pyrimidine 3, 5 -diaminonu-deoside derivatives is possible depending on the biocatalyst employed in the process [28]. N-5 -Acylated products were obtained using CALB as a biocatalyst, whereas PSLC was selective towards the N-3 position. Molecular modeling studies... 

Protic-acid-catalyzed Michael additions (59) are subject to most of the limitations of base-catalyzed Michael additions (regioselectivity and stereoselectivity of enol generation, polyaddition, etc.), and hence, the stereochemistry has been little studied (60). At low temperatures silyl and stannyl enol ethers,+ ketene acetals, and allyl species are unreactive to all but the most reactive activated olefins. However, it was discovered by Mukaiyama and co-workers that enol ethers and ketene acetals react with a,/f-unsaturated carbonyl compounds in the presence of certain Lewis acids (4,61,62). Sakurai, Hosomi, and co-workers found that allylsilanes behave similarly (5,63,64). 

HOMe/H + i i "TT MeO H Electrophilic addition (regioselective inter alia)... 

HBr/02 1 1 H Br Free radical addition (Regioselective anti-Markownifkov)... 

Perflnoroalky lation of Heterocycles. Sodium perfluoroalka-nesulfmates decompose to their corresponding perfluoroalkyl radicals in the presence of Mn(OAc)3. The latter can react with various heterocycles, such as pyridine, quinohne, isoquinoline, and coumarin. The total yields vary between 46 and 67%, but addition regioselectivity of the perfluoroalkyl radical is low (eq 44). 

Tricarbonyl [(l-4- 7)-2-methoxy-5-methylenecyclohexa-1,3-diene]iron was found to undergo facile radical addition regioselectively at the exocyclic methylene group to yield an aromatized product upon demetallation (Scheme 32). ... 

In addition, regioselective Markovnikov hydroselenation of terminal alkynes using indium(III) selenates is also reported [97],... 

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