Regioselective protection

Alternative routes to -amino acids have also been explored and involve, stereoselective alkylation of chiral derivatives of y9-alanine [136-140], Curtius rearrangement of enantiomerically pure and regioselectively protected substituted-succinic acids [134, 141, 142] (the approach is also suitable for the synthesis of y9 -amino acids [143]), or the formation of chiral isoxazolidinone intermediates [144]. 

M. Adinolfi, G. Barone, A. Iadonisi, and M. Schiattarella, An easy approach for the acetylation of saccharidic alcohols. Applicability for regioselective protections, Tetrahedron Lett., 44 (2003) 4661 -663. 

A. Bianco, M. Brufani, C. Melchioni, and P. Romagnoli, A new method of regioselective protection of primary alcoholic function with rare earths salts,... 

Regioselective protection of the pentaol 230 with bis-trichloromethyl carbonate and subsequent acetic anhydride treatment affords the C-10 acetoxy C-l, C-2 carbonate compound 231 in good yield. Deprotection of the acetonide function and regioselective silylation of the C-7 hydroxyl group, followed by... 

Me3SiCN reacts with both saturated and unsaturated aldehydes and ketones to given silylated cyanohydrines. This reaction has been particularly useful for the regioselective protection of a carbonyl in p. quinones and p. quinol antibiotic metabolite has been prepared. 

Modification of Neamine Regioselective Protection of the Amino Groups Using Metal Chelation... 

Aspects of selectivity in reaction pathways may be considered under the following topic areas chemoselectivity, regioselectivity, protection and, finally, stereoselectivi ty. 

The bulky triphenylmethyl or trityl (Tr) group is often employed for the regioselective protection of a primary sugar alcohol. It is conveniently introduced into partially protected sugar derivatives by treatment with trityl chloride (TrCl) in pyridine (Scheme 2.8).19 The protection can be slow but the addition of 4-(dimethyl)aminopyride (DMAP) or 1,8-diazobicyclo[5.4.0]undec-7-ene (DBU) can accelerate the reaction. 

After the simultaneous protection at 04 and 06, the differentiation of the remaining 2-hydroxyl and 3-hydroxyl is puzzling for glucosides because they are both secondary and equatorial. Conditions reported in the literature usually result in mixtures of regioisomers [6], For example, the regioselective protection of diol 59 via a copper complex intermediate gave the 3-0-acylated derivatives 61 and 63 as the major products in moderate yields (Scheme 2.20) [172], Nonetheless, 2-0-benzoylation... 

There are fire risks associated with the use of sodium hydride and alternative, innocuous bases would be welcome for large scale work One possibility is a mixture of barium oxide and barium hydroxide octahydrate in DMF. In the example shown in Scheme 4 191,355 the reaction is quite slow (7 days) and the yield only 55% but the method deserves further scrutiny. Another metal alkox-ide-based procedure for the regioselective protection of an equatorial alcohol proceeds via the stannylene derivative (see section 4,3.3)356... 

Cp3)2C6H3B(OH)2 is useful for the regioselective protection of amino groups (Sch. 4) [169]. For example, verbacine has been synthesized by adding cinnamoyl chloride to a 1 1 mixture of 16-phenyl-2,6,ll,15-tetraazacycloheptadecan-l-one and... 

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