From ortho esters

Pyridazinecarbohydrazides are prepared in the normal way from an ester or acid chloride and hydrazine or a substituted hydrazine, generally in good yields. Pyridazines with two ortho alkoxycarbonyl groups give cyclic hydrazides with hydrazine, which are pyridazinopyridazines. 

PINNER Imlno Ether Synthesis Synthesis of imlno ethers, amidines and ortho esters from nitnles. 

Mono MOM derivatives of diols can be prepared from the ortho esters by diiso-butylaluminum hydride reduction (46-98% yield). In general, the most hindered alcohol is protected. ... 

The mixed ortho ester formed from tri(2-chloroethyl) orthoformate (100°, 10 min-2 h, 16% yield) is more stable to acid than is the unsubstituted derivative, but can be cleaved with 80% AcOH (20°, 1 h). ... 

Ortho esters are among the few derivatives that can be prepared from acids and esters that protect the carbonyl against nucleophilic attack by hydroxide or other... 

Strong nucleophiles such as Grignard reagents. In general, ortho esters are difficult to prepare directly from acids and are therefore more often prepared from the nitrile. Simple ortho esters derived from normal alcohols are the least stable in terms of acid stability and stability toward Grignard reagents, but as the ortho ester becomes more constrained its stability increases. 

When enantiomerically pure fni/is-2-acetoxycyclohexyl tosylate is solvolyzed, tiie product is racemic /mn -diacetate. This is consistent with the proposed mechanism, since the acetoxonium intennediate is achiral and can only give rise to racemic material. Additional evidence for diis interpretation comes from the isolation of a cyclic ortho ester when the solvolysis is carried out in ethanol. In this solvent the acetoxonium ion is captured by the solvent. 

Diborane reduction of an ortho ester that is prepared from a triol with CH3C(OEt)3, PPTS. ... 

The 1,3-dicarbonyl components can be replaced by an enol ether, which can be prepared by Claisen condensation from an ortho ester and a reactive methylene compound. ... 

A salient structural feature of intermediate 18 (Scheme 2b), the retrosynthetic precursor of aldehyde 13, is its y,r5-unsaturated ester moiety. As it turns out, the Johnson ortho ester variant of the Clai-sen rearrangement is an excellent method for the synthesis of y,<5-unsaturated esters.11 In fact, the Claisen rearrangement, its many variants included, is particularly valuable in organic synthesis as a method for the stereocontrolled construction of trans di- and tri-substituted carbon-carbon double bonds.12,13 Thus, it is conceivable that intermediate 18 could be fashioned in one step from allylic alcohol 20 through a Johnson ortho ester Claisen rearrangement. In... 

It will be recalled that lactone-derived enol triflate 102 was expected to serve as a substrate for a Murai coupling37 with the mixed cuprate reagent derived from iodo ortho ester 103 (see Scheme 17c). If successful, this C-C bond forming process would accomplish the introduction of the remaining carbon atoms needed for the annulation of the seven-membered D-ring lactone. 

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