Directing groups carbamate

In the case of cyclopentenyl carbamate in which a directive group is present at the homoallyl position, the cationic rhodium [Rh(diphos-4)]+ or iridium [Ir(PCy3)(py)(nbd)]+ catalyst cannot interact with the carbamate carbonyl, and thus approaches the double bond from the less-hindered side. This affords a cis-product preferentially, whereas with the chiral rhodium-duphos catalyst, directivity of the carbamate unit is observed (Table 21.7, entry 7). The presence of a hydroxyl group at the allyl position induced hydroxy-directive hydrogenation, and higher diastereoselectivity was obtained (entry 8) [44]. 

In aromatic compounds, potent but frustrated (their ortho positions blocked) directing groups may lead to lithiations at positions other than ortho. For example, when the carbamate 610 is treated with LDA in refluxing THE, lithiation occurs at a remote position (not peri, note) and an anionic Fries rearrangement ensues to give 611 (see Section I.B.l.d). Lactonization gives 612 (Scheme 239). ... 

The main chains in 46 are held together by a hydrogen-bonding assembly of capsules, and multiple carbamate —N" H3 O C(0)NH— bridges cross-link these chains. This is a 3D network, since the side amine groups are oriented in aU three directions. The carbamate bridges were detected by NMR spectroscopy. 

Peracids m-CPBA and CF3CO3H have been used in epoxidations of substrates with two mnable allylic directing groups expected to direct the peracids to opposite faces of the alkene. Control of face selectivity was observed and attributed to the different binding abilities of the two peracids to the various allylic functionalities, carbamate on one side of the alkene and alcohol, methyl ester, acetate, trifluoroacetate, or TBS-ether on the other. The conversion of A-mono-protected and A-di-protected cyclopent-... 

Although compounds of type 1 independent of the directing group give rise preferentially to the syn-epoxides (see 2), a simple shift of the double bond into the 1,2-position leads to diminished stereoselectivity, and if the N-benzyl carbamate is used as the directing group, a mixture of anti-epoxide and carbonate 6 is obtained, which can be focused into 6 on subsequent acid treatment. This outcome proves that in this case the anti-epoxide is by far the major product. 

The first general method for mthenium(II)-catalysed oxidative dehydrogenative alkenylation of functional arenes showed successively the ability of carboxylate, heterocycle, ketone, aldehyde, amides, esters, and carbamates to behave as directing groups for C-H bond alkenylation and could also be applied to alkenes, ferrocenes, heterocycles, and protected phenols. 

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