The meaning of synonym in typedef

The following paragraph is taken from [dcl.typedef]:

Within the scope of its declaration, a typedef-name is syntactically equivalent to a keyword and names the type associated with the identifier in the way described in Clause 8. A typedef-name is thus a synonym for another type. A typedef-name does not introduce a new type the way a class declaration (9.1) or enum declaration does.

The other relevant passage we need is from [dcl.type]

As a general rule, at most one type-specifier is allowed in the complete decl-specifier-seq of a declaration or in a type-specifier-seq or trailing-type-specifier-seq. The only exceptions to this rule are the following: … long can be combined with long.

In the following code, i1 is just a synonym for long.

typedef long i1;
typedef long i1 i2;

Thus, I expect the second line to be understood as typedef long long i2. However, MSVC2015RC fails with

Error C2146 syntax error: missing ';' before identifier 'i2'

Can anyone point to the part of the standard that invalidates my expectation?

UPDATE

My point is that, as far as I understand the grammar in [dcl.type],

type-specifier:
    trailing-type-specifier
    class-specifier
    enum-specifier
trailing-type-specifier:
    simple-type-specifier
    elaborated-type-specifier
    typename-specifier
    cv-qualifier
type-specifier-seq:
    type-specifier attribute-specifier-seq opt
    type-specifier type-specifier-seq
trailing-type-specifier-seq:
    trailing-type-specifier attribute-specifier-seq opt
    trailing-type-specifier trailing-type-specifier-seq

a decl-specifier-seq does allow for a sequence of type specifiers as long as they satisfy the combination rules. It seems to me that a type is not the same as a type-specifier even though a type is specified by a type specifier ;-)

Solution

Alright, I'll answer.

First, looking at this:

a typedef-name is syntactically equivalent to a keyword

This only means that typedef-names follow the syntax of keywords. This does not mean that a typedef-name is equivalent to any particular keyword. It's like a new, unique keyword.

Then we have,

A typedef-name is thus a synonym for another type.

So, given typedef long i1;, what is this "another type"? It is long int, not just long.

In addition, what is a "type"? At the least, type-specifier is not a type. The type-specifier long represents the type "long int" (see Table 10 of n3337 or Table 9 of n4296).

I'll copy my comment here:

i1 is a synonym for the type that is long int. It is not a synonym for the keyword long. Otherwise you could also say i1 double and get a long double.

Though perhaps I should have said, i1 is not a synonym for the type-specifier long, but it is a synonym for the type long int.