Hexopyranose derivatives

The study of Lemieux and co-workers (38, 39) which first delineated the stereospecific dependences of the P.M.R. parameters of pyranose derivatives has since been confirmed by many workers (24, 40, 44). In the following section we shall discuss some of the more recently recognized stereospecific dependences, dealing first with the dependences of coupling constants and then with those of chemical shifts. Reference will be made to the P.M.R. parameters of the hexopyranose derivatives which were obtained in experiments outlined in the previous section, together with the parameters of the a-(4) and, / -(5) anomers of 1, 3, 4, 6-tetra-0-acetyl-2-deoxy-D-arafoino-hexopyranose. 

Stereospecific dependencies of the nonselective relaxation-rates for other protons in a sugar molecule may be seen in the data for a set of 3,4,6-tri-O-acetyl-l-0-benzoyl-2-deoxy-2-bromo-D-hexopyranose derivatives (40-42), as well as other 2-halogeno derivatives. A comparison of their... 

This process (also known as the Ferrier II Reaction ) has proved to be of considerable value for the efficient, one-step conversion of 5,6-unsaturated hexopyranose derivatives into functionalized cyclohexanones useful for the preparation of such enantiomerically pure compounds as inositols and their amino, deoxy, unsaturated and selectively O-substituted derivatives, notably phosphate esters. In addition, the products of the carbocyclization have been incorporated into many complex compounds of interest in biological and medicinal chemistry. ... 

T.-M. Cheung, D. Horton, and W. Weckerle, Preparative synthesis of 3-amino-2,3,6-trideoxy-L-/yv<9-hexopyranose derivatives, Carbohydr. Res., 74 (1979) 93-103. 

B. Highly Functionalized Cyclopentanes from Hexopyranose Derivatives... 

B. Highly functionalized cyclopentanes from hexopyranose derivatives 559... 

Since the mid-1980s, Kunz and co-workers started an exploration of asymmetric synthesis using sugar template-based chiral auxiliaries. Their early success on this topic is particularly shown by their demonstration of the utility of six-membered pento- and hexopyranose derivatives such as per-O-pivaloylated /3-D-galactosylamine [42,43,44,45,46,47,48,49,50]. The collective studies of the Kunz group have been thoroughly reviewed [51,52]. 

On the other hand, pentopyranoses derivatives in solution do not exhibit the conformational effects observed with hexopyranose derivatives. In a chloroform solution of the g-D-ribo derivative, the conformation with an axial chlorine is... 

Scheme 2.13 Nucleophilic ring opening of 1,2-anhydro-a-o-hexopyranose derivatives with tetrabutylammonium fluoride (TBAF) [40],...

Compounds of this class, for example, hexopyranose derivatives having the general formula (123) (see Table II), have most frequently been prepared from the corresponding 6-deoxy-6-iodo or 6-bromo-6-deoxy derivatives of suitably protected aldohexoses or aldohexosides by allowing them to react at room temperature with silver fluoride in pyridine. Alternatively, for example, the 5,6-unsaturated derivative of 1,2 3,4-di-O-iso-propylidene-a-D-galaotopyranose was prepared from the 6-deoxy-6-iodo compound by heating at 130° with sodium methoxide in methanol. Properties of some members of this class are given in Table II. 

K. Bock and C. Pedersen, Reaction of sugar esters with hydrogen fluoride. XV. Ring contraction of some hexopyranose derivatives, Acta Chem. Scand, B30 (1976) 777-780. 

Our interest in GOase came from a need to find an efficient process for making 5-C-hydroxymethyl-L-arabino-hexopyranose derivatives 1 (Equation 1). These compounds have been developed as candidates for nonnutritive sugar substitutes in foods because they resist metabolism and have sucrose-like functional properties (7). These materials would be too expensive if made using the techniques of traditional chemical synthesis, so we developed a simple "one-pot" process (Equation 1) using GOase. 

Bromination at C-5 of hexopyranose derivatives gives access to aldos-5-ulose derivatives (see Chapter 7). 

The liquid crystalline properties of dialkylacetals 1 have been described. In the presence of DDQ as catalyst, hexopyranose derivatives having fiee hydroxyl groups at C-6 or at C-S and C-6 reacted with 2,2-dimethojQ propane and acetone to give primary acyclic isopropylidene mixed acetals (e.g., 2 - 3). Non-symmetrical alaketals 5 have been prepared by use of monochloro-dialkyl 4-pentenyl rilyl ethers 4 as reagents, as shown in Scheme 1. ... 

C N.m.r. measurements have been used to assign the configuration of the branch carbon in pairs of 3-C-hydroxymethyl and 3-C-methyl branched-chain l,2 4,6-di-0-acetalated hexopyranose derivatives by comparison with the Z and E isomers of 4-t-butyl-l-hydroxymethylcyclohexanol and with corresponding diacetals of o-glucose and D-allose, ... 

Benzoyl migration from 0-4 to 0-3 of a 2,6-dideoxy-D-arabino-hexopyranose derivative is referred to in Section 3 of this Chapter. 

Treatment of the branched 3-deoxy-D-ribo-hexopyranose derivative (1) with propane-l,3-dithiol and aqueous HQ gave the 2,5-anhydro compound (4) in 80% yield (Scheme 1). The reactiim is thought to proceed via the expected acyclic dithioacetal (2) and to involve the well known elimination of a hydroxyl group P to a dithioacetal function, followed by an unprecedented intramolecular H -catalysed additmi to the p-carbon of theketoie dithioacetal (3). The synthesis of KDO by use of bis(ethylthio) intermediates is referred to in Qiapter 16. 

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