Regioselectivity Schmidt reactions

Acetyl-3-arylsydnones (164) undergo the regioselective Schmidt reaction to give 3-arylsydnone-4-A -methylcarboxamides (165) in good yields without formation of 4-acetamidosydnones (equation 49). In contrast to this, the Beckmann rearrangement of the oxime of (164, Ar = phenyl) does not proceed at all. 

Thienobenzazocine 179 is formed regioselectively in 65-93% yield when the rearrangement is carried out in PPA or PPA in xylene. The use of H2SO4 or PCI5 gives a mixture of regioisomers 179 180 in ratios from 90 10 to 60 40. The Schmidt reaction forms only thienobenzazocine 179 in 25-65% yield from benzo[4,3]-cyclohepta[l,2- 7]thiophen-4-one 181 (Scheme 50). 

The Schmidt reaction is closely related to the Beckmann reaction (equation 34). Acyclic and cyclic ketones are transformed to amides and lactams by treatment with hydrogen azide. With bridged bi-cyclic ketones, the regioselectivity of the migration is opposite to the direction of the Beckmann reaction. The Schmidt reaction has been applied to asymmetric synthesis starting from optically active a,a-dialkylated -keto esters. High chemical and optical yields have been obtained (equation 35). ... 

The Schmidt reaction of the tertiary alcohol 111 is used as a key step in the synthesis of nicotine. The reaction proceeds through 112, which undergoes a regioselective ring expansion to give imine 113. 

Thiazolidine rings are normally easy to prepare but this year a new reaction has appeared in which the ring system was produced during a thermally-induced intramolecular eliminative rearrangement. The azido-enones (364) were heated to 140 C leading to a mixture of the products (365) and (366) in equal proportions. The authors have determined that an intramolecular acid-catalysed Schmidt reaction is not involved, and have proposed the triazoline (367) as a reasonable intermediate. They have also shown that in certain cases rearrangement coupled with desulphurization provides a completely regioselective method for conversion of 2-cycloalkenones to the ene lactams (368). 

The lack of regioselectivity, the limitation that tertiary or benzylic alcohols must be used as precursors to Schmidt reactions with carbocations, and the harsh Lewis acidic... 

The Schmidt group reported another synthesis of rat brain Thy-1 GPI in 1999 [52], In 2003, they reported a rather similar synthesis [53] that involved differentially protected phosphoethanolamine groups useful for future regioselective protein/ peptide coupling reactions. This differentiation was made possible by using Cbz and te/t-butoxycarbonyl (Boc)-protected phosphoramidite reagents that could be... 

Tetramethoxy-5,6,ll,12-tetrahydrodibenzo[ ,i ]cycloocten-5-one 302 was reacted with hydroxylamine-O-sulfonic acid and underwent a one-pot Beckmann (formic acid, reflux) or Schmidt (DMF, reflux) rearrangement to afford the 6-oxodibenzo[, /]-azonine 304 (Equation 42). Regioselectivity of the process was assigned based on H NMR data and on model reactions to prove preferential migration of the 3,4-dimethoxyphenyl over the 3,4-dimethoxybenzyl group <1996T8063>. 

RAJ O FIair, MA Freitas, S Gronert, JAR Schmidt, TD Williams. Concerning the regioselectivity of gas phase reactions of glycine with electrophiles the cases of the dimethylchlorinium ion and the methoxymethyl cation. J Org Chem 60 1990-1998, 1995. 

Schmidt glycosylation [8b] was used twice to prepare the trisaccharide donor 17 (Scheme 9). Attempts to use xylopyranosyl imidate donor 28 in the regioselective glycosylation of diol 26, which has an equatorial 3-OH and an axial 4-OH as diol 11, were not successful. The deprotection of the anomeric allyl group of trisaccharide 29 was found to be problematic. When reactions were catalyzed by palladium spe-... 

Chalcones (123) are commonly prepared by Claisen-Schmidt or aldol condensation. An important way to synthesize chalcones (123) is the Friedel-Crafts acylation involving treatment of acid chlorides (121) with arenes (122). Such a protocol for the synthesis of chalcones (123) was developed by More et al. (2012) using nano-ZnO heterogeneous catalyst under solvent-free conditions at room temperature (Scheme 9.38). Arenes (122) of all sorts, activated as well as unactivated, reacted smoothly to afford the chalcones (123) in excellent yield. High regioselectivity was observed during the course of reaction, which occurred selectively at the para-position of OMe, Br, Me, and Cl. 

Schmidt, A.F., T.A. Vladimirova, E.Yu. Schmidt, and T.V. Dmitrieva. 1995. Regioselective a-arylation of N-vinylpyrroles by Heck reaction. Izv Akad Nauk Ser Khim 4 786. 

Schmidt, A.R, T.A. Vladimirova, and E.Yu. Schmidt. 1997. Regioselectivity of the olefin introdnction stage across the Pd-C bond in Heck reaction. Kinet Catal 38 (2) 26S-273. 

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