Carbinol carbon

Efficient kinetic resolution of chiral unsaturated secondary alcohols by irreversible enzyme-mediated acylation (with vinyl acetate as acylating agent, a crude preparation of Pseudomonas AK, and hexane as solvent) is possible, provided one relatively large and one small substituent are attached to the carbinol carbon. However, the method can be used to resolve substrates that are not amenable to asymmetric epoxidation (see examples 23, 25, 27, 29, where the double bond is either deactivated by an electron-withdrawing substituent, or is of the propargyl alcohol type). Acylation of the / -enantiomer consistently proceeds faster than that of the 5-enantiomer. An example of an allenic alcohol was also reported248. 

ROH is an alcohol and ArOH is a phenol (Chapter 19). Some alcohols have common names, usually made up of the name of the alkyl group attached to the OH and the word alcohol" e.g., ethyl ilcohol, C2H5OH. More generally the lUPAC method is used, in which the suffix -ol replaces the -e of the alkane to indicate the OH. The longest chain with the OH group is used as the parent, and the C bonded to the OH is called the carbinol carbon. 

Oxidation. Alcohols with at least one H on the carbinol carbon (1° and 2°) are oxidized to carbonyl compounds. 

Cyclofunctionalization of homoallylic alcohols with bis(sym-collidine)iodine(I) perchlorate produces oxetanes in good yield if the 4-exo mode of cyclization is favored electronically by the alkene substitution pattern (Table l).14 Geminal substitution at the carbinol carbon also favors this mode of cyclization (compare entries 2 and 3 with entry 1). Substitution at C-3 leads to reaction only by the 4-exo mode (entry 4), while substitution at C-4 leads to cyclization only via the 5-endo mode (entry 5). 

A more striking example of the influence of conformation on the reaction outcome is seen in the nitrous acid deamination of 2-aminocyclohexanols which takes place by rearrangement of a group on the carbinol carbon that is anti to the developing carbocation. The deamination reaction is very fast and the products reflect the population of the chair conformers. The trans isomer exists mainly in the diequatorial conformer thus the only group anti to the amino... 

Kinetic resolution of chiral aUylic alcohols.7 Partial (at least 60% conversion) asymmetric epoxidation can be used for kinetic resolution of chiral allylic alcohols, particularly of secondary allylic alcohols in which chirality resides at the carbinol carbon such as 1, drawn in accordance with the usual enantioface selection rule (Scheme I). (S)-l undergoes asymmetric epoxidation with L-diisopropyl tartrate (DIPT) 104 times faster than (R)-l. The optical purity of the recovered allylic alcohol after kinetic resolution carried to 60% conversion is often > 90%. In theory, any degree of enantiomeric purity is attainable by use of higher conversions. Secondary allylic alcohols generally conform to the reactivity pattern of 1 the (Z)-allylic alcohols are less satisfactory substrates, particularly those substituted at the /1-vinyl position by a bulky substituent. 

We have systematically examined the facility with which DTPP promotes the cyclodehydration of simple diols to cyclic ethers 1,3-propanediol (1) - oxetane (2) (2-5%) 1,4-butanediol (3) te-trahydrofuran (4) (85%) 1,5-pentanediol (5) - tetrahydropyran (6) (72%) 1,6-hexanediol (7) - oxepane (8) (55-68%). Increased alkyl substitution at the carbinol carbon s gnificantly diminishes the facility for cyclic ether formation. For example, a mixture of meso- and d, 1 —2, 6-heptanediol gave only 6-10% of the cis- and trans-2,6-dimethyltetrahydropyrans when treated with DTPP. While diol 1 resists cyclodehydration with DTPP to oxetane, some 2,2-di-substituted 1,3-propanediols are readily converted to the appropriate oxetanes [e.g., 2-ethyl-2-phenyl-l,3-propanediol -> 3-ethyl-3-phenyloxetane (78%)]. 

We can begin with either a carbon or a proton resonance and obtain equivalent results. We will use the carbon axis as our starting point because we usually have less overlap there. For example, a line drawn parallel to the proton axis at about 68 ppm on the carbon axis (the carbinol carbon) intersects five cross peaks none of the five correlations corresponds to the attached proton (VCH) at 3.8 ppm. Four of the cross peaks correspond to the two pairs of diastereotopic methylene groups (2.48, 2.22,1.45, and 1.28 ppm) and these represent, 2iCH, or two-bond couplings. The fifth interaction (3/CH) correlates this carbon atom (68 ppm) to the isopropyl methine proton (1.82 ppm), which is bonded to a carbon atom in the /3-position. The other carbon atom in a /3-position has no attached protons so we do not have a correlation to it from the carbinol carbon atom. Thus, we have indirect carbon connectivities to two a-carbons and to one of two /3-carbons. 

Answer D is a tertiary alcohol which can he prepared by using Grignard reagent and a ketone. Note that the alkyl group is attached to the carbinol carbon, thus this compound can readily be made by a Grignard reaction. 

Answer Tiie best C—C bond to break in a cyclic aliphatic aicohol is the bond which attaches the alkyl substituent to the carbinol carbon as indicated below... 

Since wc lire going to have to connect the large aliphatic group to tiie ring at some stage of the synthesis, it will Ik easier if we select C in which the carbinol carbon is attached directly to the ring. 

How can C be broken up so that the structures of the required Grignard reagent and ketone may be deduced Answer Since C is a tertiary alcohol, there are three carbon-carbinol carbon bonds which may be cleaved to reveal the needed starting materials. 

Answer Since E is a tertiary alcohol, it can be prepared from a Grignard reagent and a ketone. Being a tertiary alcohol there arc three possible ways of breaking up the molecule by cleaving carbon-carbinol carbon bonds. As... 

How can A be broken up so that the structures of the desired aldehyde and Grignard reagent can be deduced Answer A can be broken up in two ways by cleaving the carbon-carbinol carbon bond as illustrated below. 

Answer C being a secondary alcohol can lie prepared by reacting a Grignard reagent to an aldehyde according to procedure Vl-4b. Since C is a secondary alcohol, it can lie broken up in two ways, namely by cleaving eadi of the carbinol carbon-carbon bonds as illustrated below. 

Answer To find the needed starting materials, the bond between the a- and 0-carbons must be cleaved as shown below. The carbinol carbon in the product must be the carbonyl carbon in the starring aldehyde or ketone as is shown in procedure XIV-3. 

Upon aqueous workup, these provide secondary (R = H) or tertiary (R + H) alcohols F. These compounds contain two identical substituents at the carbinol carbon both of which originate from the nucleophile. 

M. Kasha Comparative Effects of Radiation (ed. M. Burton, J. S. Kirby-Smith, and J. L. Magee) Wiley, New York 1960, p. 72-97, note esp. pages 87-89 (b) The presentation in Ref. 27 a needs to be modified slightly in the present discussion to conform to current organic mechanisms. For example, hydrogen abstraction is from a carbinol carbon rather than from the oxygen. 

Cyanogen bromide reacts with threo- 2-piperidyl carbinol (278) to form the trans imine (279). The latter is also formed from the erythro 1-carbamate (280) using thionyl chloride for the cyclodehydration reaction. The latter reaction therefore proceeds by inversion of the configuration at the carbinol carbon atom (73AP284). 

---