C intramolecular

In the reaction of aHyl alcohol with carbon monoxide using cobalt carbonyl, Co(CO)g as the catalyst, in the presence of a small amount of hydrogen and carbon monoxide under pressure, 9.8 MPa (1420 psi), at 100°C, intramolecular hydroesterification takes place, yielding y-butyrolactone [96-48-0] (16). 

Difluoroaminofluorodiazirine (225) extrudes nitrogen at only 75 °C. Intramolecular stabilization gives trifluoromethylenimine (226) added tetrafluoroethylene is cyclopropa-nated. This type of dichotomy is not often found in carbene chemistry alkylcarbenes undergo intramolecular stabilization as a rule, whereas intermolecular stabilization is observed exclusively with alkoxycarbonylcarbenes and with difluorocarbene. In the latter case CF2 attacks its precursor when no other reaction partner is present. 

Finally, the synthesis of 4//-3,l-benzoxazines 239 via a tandem aza-Wittig reaction (Scheme 89) should be mentioned. Carbodiimide 238 or isocyanate generated by an intramolecular aza-Wittig reaction bears an o-hydroxymethyl group on the A(-aryl substituent this OH attacks the carbodiimide C intramolecularly with cyclization to give a 3,1-benzoxazine (91S21). 

C) Intramolecular acylation of amino acids and their derivatives. 

A new synthesis of pyrrolizidine, which is based on the reaction of bis-tertiary glycols with co-chloronitriles, was reported by Meyers and Libano.28 The method involves three steps (a) condensation of 2,5-dimethyl-2,5-hexanediol (48) with 4-chlorobutyronitrile in the presence of sulfuric acid to give a derivative of A 1-pyrroline (49), (6) reduction of 49 with sodium borohydride to give the corresponding pyrrolidine (50), and (c) intramolecular cyclization of the pyrrolidine in the presence of alkali to give the pyrrolizidine derivative 51. The three-step synthesis was performed without isolation of the intermediate products. 

C. Intramolecular Carbene Reactions with Substituents Attached to... 

---