Carbon-Heteroatom Single Bond

If the target molecule is monofunctional, the disconnection process is classified as a one-group disconnection. The bond initially considered for cleavage would be, if present, the a-carbon-heteroatom single bond (i.e. the C—O, C—X, C—N, C—S bonds) as would be found in, for example, alcohols (Section 5.4), alkyl halides (Section 5.5), ethers (Section 5.6), nitroalkanes (Section 5.15), amines (Section 5.16), thiols and thioethers (Section 5.17). 

Rotation about sp2 carbon-heteroatom single bonds is usually a higher energy process compared to rotation about sp3 carbon-heteroatom single bonds due to conjugation and to resulting partial double bond character of the pivot bond. Compare the barrier of methanol (1.07 kcal/mol, Table 7) and ethanol (1.34 kcal/mol) with that of phenol (3.1 kcal/mol) [83]. 

Reduction of carbon-carbon and carbon-heteroatom single bonds... 

Ionic hydrogenation is the noncatalytic addition of hydrogen to carbon-carbon or carbon-heteroatom double bonds, and the hydrogenolysis of carbon-oxygen or carbon-halogen single bonds. Thus, the conversion of aldehydes and ketones to the corresponding hydrocarbon is one of its many manifesta-... 

Single bond between carbon and nonhalogen heteroatom... 

Heteroatoms, such as nitrogen, oxygen and sulphur, promote cleavage of an adjacent carbon-carbon single bond by forming an ion in which the lone-pair electrons participate in resonance stabilization ... 

The epoxide functionality has tremendous versatihty in the preparation of complex molecules, since its treatment with a nucleophile affords an alcohol, two contiguous stereocenters, and a new carbon-carbon or carbon-heteroatom bond in a single step. 

A useful aspect of the mercury(II) hydride method is that it can be directly coupled with the many standard techniques for heteromercuration of alkenes and cyclopropanes. The resulting overall transformation adds a heteroatom and a carbon atom across the carbon-carbon double bond of an alkene or the carbon-carbon single bond of a cyclopropane. This is a difficult transformation to conduct by standard ionic techniques. An alkene thus becomes an equivalent of synthon (12) and a cyclopropane of synthon (13 Scheme 34). Many equivalent transformations (like haloetherification and phenylselenolactoniza-tion) are available to make precursors for tin hydride mediated additions. 

A synthon may be defined as a structural unit which becomes an idealised fragment as a result of disconnection of a carbon-carbon or carbon heteroatom bond in a retrosynthetic step (transform). Thus it may be envisaged in general terms, that an open-chain structure in a single disconnection step would give rise to two synthons two synthons would also arise in a similar disconnection of a... 

---